Sustainable Consumption Intentions Among Portuguese University Students: A Multidimensional Perspective

Abstract

This study examines sustainable consumption intentions among university students in Portugal, a generation increasingly recognized for their ecological awareness but often constrained by structural and social barriers. Within this context, this study explores psychological and behavioral determinants of sustainable consumption and peer recommendation using an integrative framework based on the Theory of Planned Behavior (TPB), the Value–Belief–Norm theory (VBN), and the SHIFT model. Drawing on a survey of 324 students from diverse academic backgrounds, we analyzed how environmental beliefs, consumer habits, and activism influence sustainable consumption intention and recommendation. The analysis, conducted using Partial Least Squares Structural Equation Modeling (PLS-SEM), reveals that environmental beliefs significantly predict both consumer intention and habitual behavior, which in turn affect activism and sustainable consumption. Notably, intention emerges as a key mediator between individual motivations and peer recommendation, while activism and habits do not exert direct influence on recommendation behavior. These findings underscore the importance of moral values, routine behavior, and motivational pathways in shaping sustainable practices, while highlighting the persistent gap between awareness and consistent advocacy. This study offers theoretical and practical insights into how structural and psychological factors can reinforce youth engagement with sustainability.

1. Introduction

Sustainable consumption has become a central concern in academic and policy spheres, especially within the context of younger generations. University students represent a critical demographic class in promoting sustainable behavior, due to their exposure to environmental education, digital mobilization platforms, and a growing sense of ecological responsibility. Despite widespread environmental awareness and the endorsement of sustainable values, a persistent discrepancy remains between students’ stated intentions and their actual behavior [1,2].

In recent years, youth have been increasingly portrayed as the forefront of the global environmental movement. From international initiatives like Fridays for Future to their participation in high-profile climate campaigns, young people have emerged as symbols of ecological consciousness and civic engagement [3,4]. This has reinforced the notion of an “Environmentally conscious generation”, suggesting that contemporary youth are inherently more aligned with environmental values, more likely to participate in activism, and more inclined to adjust their consumption patterns in line with ecological values. However, although this narrative has gained importance, there is insufficient empirical evidence to determine whether such attitudes translate into consistent, long-term behavioral change [5,6].

University students are uniquely positioned within this discourse, given their access to environmental knowledge, peer-driven social norms, and sustainability-focused communication [7,8]. Nevertheless, previous research highlights the persistent “attitude–behavior gap”, whereby individuals with high environmental concern often fail to consistently adopt sustainable practices [9,10]. This inconsistency is influenced by a range of mediating variables including financial constraints, convenience, peer influence, and lack of institutional support [11,12,13].

Furthermore, the existing literature tends to focus on isolated pro-environmental behavior, such as recycling or participation in climate strikes, while neglecting broader issues such as activism, daily consumption patterns, and the role of moral and social norms. Additionally, limited attention has been given to the specific cultural and socio-economic contexts of Southern Europe, where youth engagement with sustainability may be shaped by economic precarity, limited institutional trust, and distinct consumption dynamics [12,13,14,15,16,17,18,19].

In Portugal, despite growing public concern about environmental issues and increasing awareness of sustainability principles [20], empirical data on youth behavior remain scarce. Emerging studies suggest high levels of concern and egocentric attitudes [21,22], yet there is limited evidence on how these translate into actual practices or collective action. As such, further research is needed to understand the interplay between environmental attitudes, consumption behavior, and activism among Portuguese university students.

This study seeks to address these gaps by exploring the environmental awareness, sustainable consumption habits, and civic engagement intentions of university students in Portugal. This research aims to evaluate the extent to which this group reflects the values and behavior attributed to the “Environmentally conscious generation”. The following research questions guide the analysis: (i) To what extent are students environmentally aware and motivated to act? (ii) How do their consumption choices reflect sustainable values? (iii) What barriers limit the translation of pro-environmental attitudes into consistent behavior?

By providing a multidimensional and empirically grounded analysis, this study contributes to a more nuanced understanding of youth engagement with sustainability. It challenges generalized assumptions about generational environmentalism and emphasizes the importance of structural conditions, educational strategies, and cultural frameworks in fostering sustainable behavior among young people.

2. Literature Review

The intention to adopt sustainable consumption behavior among university students is shaped by a complex interplay of psychological, cognitive, normative, social, and contextual factors. The literature in environmental psychology, consumer behavior, and sustainability marketing highlights the roles of environmental beliefs, moral values, social norms, education, activism, and structural constraints in influencing pro-environmental attitudes and actions. However, despite increasing awareness, a persistent “intention–behavior gap” remains a central challenge, especially among young adults [1,2].

Understanding sustainable consumption among youth requires an integrative approach that captures not only cognitive and attitudinal antecedents, but also moral motivations and behavioral mechanisms. To that end, this study combines three influential theoretical frameworks (Theory of Planned Behavior (TPB), Value–Belief–Norm theory (VBN), and the SHIFT behavioral framework) to construct a multidimensional explanatory model.

The Theory of Planned Behavior [23] provides the predictive foundation of the model, positing that behavioral intentions are determined by attitudes toward the behavior, subjective norms, and perceived behavioral control. In sustainability research, TPB has been widely applied to explain how individuals form intentions to act in environmentally responsible ways, particularly through rational evaluation of expected outcomes [10,24]. This model is particularly relevant to understand future-oriented decisions such as consumption choices or the likelihood of recommending sustainable actions to others.

While TPB emphasizes rational decision-making, it does not fully account for moral and normative motivations. To address this gap, the Value–Belief–Norm theory (VBN) is incorporated, as it explains how internalized moral values and ecological worldviews influence personal norms and pro-environmental behavior [25]. The VBN model is especially useful for understanding how biospheric and altruistic values, combined with beliefs about environmental threats, lead to moral obligations and behavioral consistency [26,27]. Within this study, VBN theory supports the inclusion of environmental beliefs and activism as morally driven issues, rooted in perceived responsibility and ethical concern.

To bridge the gap between intentions and actual behavior, the SHIFT framework [28] is used to operationalize how sustainable actions are influenced by psychological and situational factors. SHIFT, an acronym for social influence, habit formation, identity, feelings, and tangibility, provides a behavioral lens that addresses the shortcomings of both TPB and VBN by emphasizing non-rational drivers, emotional cues, and the importance of visibility and reinforcement. This model helps explain why students with strong environmental values may still fail to act unless supportive social and structural conditions are in place. It is particularly relevant for understanding the mechanisms of peer recommendation, habitual behavior, and identity-based advocacy, which are central to this study.

Taken together, TPB, VBN, and SHIFT offer a complementary and multidimensional framework: (i) TPB clarifies how beliefs and social norms translate into behavioral intention, (ii) VBN captures the moral and affective dimensions underlying environmental concern and activism, (iii) SHIFT explains how and when intentions are converted into real behavior and social influence.

This integrated framework allows for a more holistic understanding of sustainable consumption among youth by combining rational, normative, and behavioral perspectives. It also enables the modeling of direct, indirect, and mediated pathways between beliefs, habits, intention, and social influence—providing theoretical robustness and practical relevance.

Environmental knowledge and risk perception consistently emerge as foundational antecedents of sustainable behavioral intentions. Studies indicate that increased environmental literacy, especially when fostered through education, heightens concern and supports sustainable choices [2,15,29,30,31]. Environmental education plays a crucial role in strengthening these links, with evidence showing that structured learning interventions significantly boost pro-environmental intentions [32,33,34].

Equally important are values-based predictors. Altruistic and biospheric values, reflecting care for others and nature, significantly influence environmental beliefs and personal moral norms, which in turn drive sustainable behavior [2,26,27,35]. These internalized beliefs support higher levels of moral reasoning and behavioral consistency, particularly in consumption domains such as food choices and waste reduction [36].

Nevertheless, this foundation does not always lead to behavior. The “attitude–behavior gap” remains a recurrent finding, with environmentally conscious students often failing to consistently enact their beliefs [9,10]. Research shows that while specific and visible actions—such as opting for tap water over bottled water—are more likely to align with intention, habitual or less visible practices, such as avoiding plastic bags, tend to show weaker correlations [37,38].

Social norms are especially influential within university contexts, where peer influence can either reinforce or inhibit sustainable practices [2,26,35,39] highlight the role of social responsibility and external incentives, while [40] demonstrates that activating social norms, especially when paired with persuasive messaging, can significantly reduce unsustainable behavior.

Educational strategies further moderate the intention–behavior relationship. Participation in courses related to sustainability and circular economy has been found to enhance sustainable intentions and reduce gender differences in environmental attitudes [41]. However, findings on gender remain mixed [42], and some contextual facts, such as collectivist values, appear to exert less influence than expected [39].

In parallel, sustainable marketing and communication strategies have a direct impact on shaping youth consumption behavior. Transparency regarding corporate environmental practices enhances consumer trust and reinforces alignment with sustainable brands [43,44]. When combined with authentic corporate social responsibility, sustainability messaging not only strengthens brand image but also promotes behavior consistent with ecological values [45].

Social media and digital marketing have become key tools for engaging youth in sustainable consumption. Campaigns driven by influencers and high-quality digital content have proven effective, particularly among younger audiences attuned to visual and reputational cues. However, these strategies must be balanced to avoid information fatigue or technostress [46]. In some cases, poorly designed messaging may lead to rebound effects such as moral licensing, whereby individuals justify unsustainable choices following minor pro-environmental actions [47].

The literature also highlights the importance of anti-consumption practices—rejecting, reducing, and reusing, as strategies aligned with personal values and broader sustainability goals. These are more effective when embedded within supportive policy frameworks and social marketing initiatives [48,49]. Moreover, ethical and religious factors influence consumption behavior, suggesting that campaigns aligned with individuals’ belief systems are more likely to promote lasting change [50]. The SHIFT framework proposed by [28], which incorporates social influence, habits, identity, feelings, and tangibility, offers a comprehensive model for designing effective behavior-change interventions.

Recent global studies confirm the mediating role of intention in sustainable behavior [51], while highlighting cultural contingencies. Whereas Chinese students prioritize social trust [52], Portuguese youth exhibit stronger responses to institutional policies [18]. This underscores the need for context-sensitive models like ours that account for Southern European economic constraints [14,16,53].

Importantly, youth engagement with sustainability cannot be fully understood without considering regional and socio-economic contexts. Southern European countries, including Portugal, face distinct challenges such as higher youth unemployment, lower institutional trust, and conservative consumption habits [14,16]. Despite strong sustainability attitudes among Mediterranean European youth, actual sustainable consumption remains low (7–17% in Portugal, 11% in Spain), influenced by economic constraints, generation-wise differences, and country-specific barriers like limited product knowledge in Greece [54].

Historically, some rectors of Portuguese universities have demonstrated a commitment to sustainable development (SD), as expressed in the Copernicus Declaration of 1994. However, between 2005 and 2014, Portuguese higher education institutions (HEIs) were classified as “laggards” or part of the “late majority” regarding the integration of SD into education, sustainability research, and inclusive development, particularly when compared to other Southern European countries [55,56].

More recent studies, however, highlight notable progress by Portuguese HEIs in implementing concrete actions aligned with the Sustainable Development Goals (SDGs) [57]. Findings from [58] demonstrate that the key competencies outlined in the sustainability reference framework (systems thinking, anticipatory, normative, strategic, and interpersonal competencies) are reflected in recent research on education for sustainability in Portugal.

According to [59], public HEIs in Portugal must foster an institutional commitment to sustainability, adopting and promoting sustainable development practices through tangible actions that contribute to a livable campus environment. These dimensions are essential for enhancing student satisfaction and attracting international students.

Portuguese studies reveal high levels of environmental concern among students [29], alongside support for circular practices, yet also underscore uncertainty regarding the effectiveness of individual actions in influencing systemic change [22].

Finally, while young people are frequently portrayed as agents of sustainability, the literature presents a more nuanced picture. Awareness and intentions are high, but behavioral implementation is moderated by financial constraints, perceived efficacy, and structural support. Digital activism offers accessible forms of engagement but may not lead to long-term commitment [4,20,60]. As such, fostering sustainable behavior among students requires not only raising awareness, but also transforming university environments into supportive ecosystems that enable students to act upon their values.

Grounded in the theoretical insights discussed above, including the Theory of Planned Behavior [23], the Value–Belief–Norm theory [25], and the SHIFT behavioral framework [28], this study proposes a multidimensional model to explain sustainable consumption intentions and peer influence among university students.

While numerous studies have examined pro-environmental behavior among university students globally [2,10,26], most rely on isolated theoretical models or narrow behavioral indicators such as recycling or green purchasing. These approaches often overlook the broader motivational, normative, and social mechanisms that shape sustainable behavior among youth. Furthermore, the specific cultural and socio-economic contexts of Southern Europe, particularly Portugal, remain underrepresented in this body of research.

This study addresses these gaps by proposing and empirically testing a multidimensional model that integrates the Theory of Planned Behavior (TPB), the Value–Belief–Norm theory (VBN), and the SHIFT framework. This theoretical integration offers a novel and holistic perspective on the formation and diffusion of sustainable consumption intentions, bridging rational, moral, and behavioral dimensions. The model links environmental beliefs, consumer habits, activism, behavioral intention, and peer recommendation, thereby capturing the complexity of sustainable behavior within a single explanatory framework.

In contrast to prior research, such as [14,15], which highlights correlations between environmental knowledge and behavior, our study emphasizes the mediating role of behavioral intention, particularly its influence on peer recommendation. We contribute new insights by showing that while Portuguese university students exhibit strong environmental concern and sustainable habits, these factors alone do not directly predict social advocacy. Instead, intentional, identity-driven communication, rooted in internalized values and activated through behavioral intention, is crucial for influencing peers.

Moreover, while youth environmentalism has been widely examined in global contexts, especially through digital activism [3] and movements such as Fridays for Future [4], these studies often overlook regional disparities in structural conditions. In Southern Europe, youth engagement with sustainability is shaped by high unemployment, institutional distrust, and economic precarity [14]. By empirically situating our model in Portugal, this research adds valuable regional nuance to the broader discourse on the “Environmentally conscious generation.

Ultimately, this study offers an original contribution by demonstrating that the pro-environmental influence of youth depends not only on values or habits but on the intentional transformation of beliefs into communicative action. These findings advance existing models and enhance our understanding of how sustainability values are internalized and socially transmitted, particularly in contexts marked by structural constraints.

This study advances a multidimensional theoretical framework by integrating the Theory of Planned Behavior (TPB), the Value–Belief–Norm (VBN) theory, and the SHIFT behavioral framework to explain sustainable consumption intentions and peer-driven recommendation behavior among university students. While each model has been widely applied in sustainability research, their integration offers a multi-layered understanding that addresses the limitations of each theory.

TPB, proposed by [23], explains behavioral intention through three core components: attitudes, subjective norms, and perceived behavioral control. It provides a rational foundation for understanding why individuals tend to engage in certain behavior. However, TPB is limited in its treatment of moral and emotional motivations, and it does not fully account for the intention–action gap. This gap is addressed by integrating the VBN theory and the SHIFT model.

The VBN theory [25] contributes a normative and moral dimension by linking biospheric values, environmental beliefs, and personal norms to behavior. It explains how deeply held environmental values form the motivational basis for pro-environmental action, even in the absence of external incentives. Within our model, VBN strengthens the formation of behavioral intentions by providing the moral imperatives that underpin TPB’s attitudinal and control components. For instance, individuals who perceive environmental protection as a moral duty are more likely to develop strong, resilient intentions to act sustainably, regardless of practical constraints.

Despite their contributions, both TPB and VBN fall short in explaining when and how intentions are transformed into observable behavior. This is where the SHIFT model [28] plays a critical role. Grounded in behavioral science and social psychology, SHIFT introduces five empirically supported levers that facilitate sustainable behavior: social influence, habit formation, identity alignment, feelings, and tangibility. These elements address contextual and psychological barriers that often impede the translation of intention into action.

Social influence underscores the importance of peer visibility and normative behavior in shaping sustainability practices. Habit formation emphasizes the power of repetition in creating automatic, sustainable routines. Identity alignment promotes consistency by linking behavior to self-concept, while emotional engagement (feelings) enhances motivation beyond cognitive reasoning. Finally, tangibility increases the impact of pro-environmental actions by making their outcomes concrete and immediate. For example, university students may intend to consume sustainably due to moral and rational motives, but they are more likely to recommend or promote their behavior publicly when they align with their identity or are socially validated.

This integrated model illustrates three synergistic pathways: (1) VBN’s moral norms reinforce TPB’s intention drivers, enhancing their stability against external pressures, (2) TPB’s intentions are operationalized through SHIFT’s behavioral catalysts, particularly when social norms and identity alignment are activated, and (3) VBN’s value-based motivations shape identity and habitual behavior, which the SHIFT model identifies as crucial for sustained engagement and peer influence.

By synthesizing rational intention (TPB), moral motivation (VBN), and behavioral activation (SHIFT), this tripartite framework offers a robust and context-sensitive lens for analyzing the sustainable consumption behavior of the “Environmentally conscious generation.” It is particularly well-suited for studying university students, whose values are still forming, and whose behavior is highly susceptible to social and identity-based cues within academic and peer networks.

The model integrates five key constructs: environmental beliefs (cognitive and moral concern for environmental issues, consumer habits (existing day-to-day sustainable behavior), environmental activism (willingness to engage in civic or digital environmental action), consumer intention (future-oriented willingness to consume sustainably), and recommendation (the tendency to advocate sustainable behavior among peers).

These dimensions are interrelated, forming a system in which environmental values inform both private behavior (habits) and public engagement (activism), which in turn shape intention and peer recommendation.

The model shown in Figure 1 gives rise to the following hypotheses:

H1: 

Environmental Beliefs are positively associated with Consumer Habits.

Environmental beliefs, encompassing ecological values and cognitive awareness of environmental issues, form the psychological basis for adopting sustainable consumption behavior. According to the Value–Belief–Norm (VBN) theory [25], individuals who internalize biospheric and altruistic values tend to develop personal norms that influence daily actions such as recycling, energy saving, or reducing plastic usage. Empirical studies confirm that stronger environmental beliefs are linked to higher engagement in habitual sustainable practices [2,15,27,29]. Additionally, ref. [9] argue that while beliefs alone may not always translate into behavior, they are critical precursors when reinforced by facilitating conditions.

H2: 

Environmental beliefs are positively associated with environmental activism.

Beliefs rooted in ecological concern and moral obligation are also strong predictors of environmental activism. Youths who perceive environmental degradation as a moral issue are more likely to engage in civic actions, from climate strikes to institutional lobbying [4,59,61]. The Norm Activation Model (NAM) supports this connection, highlighting the role of awareness of consequences and perceived responsibility in triggering activist behavior [62]. Moreover, recent findings by [6] confirm that belief-based moral reasoning enhances both passive and active forms of environmental engagement among students.

H3: 

Environmental beliefs are positively associated with consumer intention.

The Theory of Planned Behavior [23] posits that attitudes—shaped by beliefs—influence intentions. In sustainability research, environmental beliefs are consistently found to predict the intention to adopt pro-environmental behavior, such as purchasing eco-friendly products or reducing meat consumption [2,10,29]. This relationship is reinforced by perceived behavioral control and the alignment of values with identity [28]. Recent studies [32,33] emphasize that students with high environmental concern also exhibit stronger intentions to consume sustainably.

H4: 

Environmental beliefs are positively associated with recommendation.

Beyond personal behavior, individuals with strong environmental beliefs are more likely to act as opinion leaders or peer influencers, encouraging others to adopt sustainable lifestyles [26,40]. This reflects mechanisms of social norm transmission and environmental identity signaling. According to the SHIFT framework, identity and social influence are key drivers of pro-environmental behavior diffusion [28]. Thus, students with solid environmental convictions may promote sustainability not only through actions but through interpersonal communication.

H5: 

Consumer habits are positively associated with environmental activism.

Habits serve as behavioral anchors that reinforce environmental identity and increase psychological consistency. Individuals who regularly have a sustainable behavior may be more inclined to engage in activism to advocate systemic change [63,64,65,66,67] highlights that habitual engagement enhances perceived behavioral control, thus supporting broader participatory behavior. Youths with strong daily practices (e.g., vegetarianism, zero-waste efforts) often express higher readiness for public advocacy [4].

H6: 

Consumer habits are positively associated with consumer intention.

Previous behavioral patterns are strong predictors of future behavioral intentions. TPB and habit theory both suggest that actions undertaken routinely increase behavioral salience and lower the cognitive cost of intention formation [68,69]. Thus, students already involved in sustainable consumption (e.g., buying local, minimizing packaging) are more likely to reinforce those intentions [2,38].

H7: 

Consumer habits are positively associated with recommendation.

Sustainable behaviors are often socially visible, and individuals who engage in them frequently tend to influence peers—either by modeling behavior or through explicit encouragement [3,70]. According to the social learning theory, observable and repeated behaviors have persuasive power, particularly in collective environments like universities. Ref. [49] also argue that habit-driven individuals are more active in promoting anti-consumption through social marketing influence.

H8: 

Environmental Activism is positively associated with Consumer Intention.

Activist engagement enhances pro-environmental identity and strengthens commitment to sustainability across behavioral domains. The feedback loop between activism and intention suggests that students involved in environmental movements often adjust their personal consumption to reflect their public stance [4,6]. This phenomenon aligns with identity consistency theories and is reinforced in collectivist or movement-driven contexts.

H9: 

Environmental activism is positively associated with recommendation.

Environmental activists often serve as peer change agents, spreading ecological norms and challenging unsustainable behavior. According to [62], those who accept responsibility for ecological outcomes are more likely to advocate behavioral change in others. Furthermore, digital activism, which is prevalent among youth, offers mechanisms for wide-scale recommendation and peer persuasion [46,50].

H10: 

Consumer intention is positively associated with recommendation.

Intentions are predictive not only of individual behavior but also of behavioral advocacy. Individuals who plan to engage in sustainable practices are more likely to recommend these actions to peers, reflecting internal consistency and value alignment [10,28]. Moreover, intention-sharing acts as a form of social reinforcement and norm building within peer groups [26].

To further clarify the theoretical foundation of our model, we associate each of the main dimensions with their underlying theories as follows: (i) environmental beliefs are rooted in the VBN theory, reflecting the role of biospheric values and ecological concern in shaping personal norms, (ii) environmental activism is informed by both VBN and SHIFT frameworks, combining internalized moral imperatives with identity and socially driven engagement, (iii) consumer habits align with the SHIFT model, emphasizing the role of routine and automaticity in sustaining pro-environmental behavior, (iv) consumer intentions derive from both TPB and VBN, incorporating rational evaluation and moral commitment in forming purposeful behavioral goals, and (v) recommendation behavior reflects constructs from SHIFT (social influence, identity expression) and TPB (normative pressure), illustrating how internal intention translates into socially observable advocacy.

This integrative framework reflects a dynamic process in which belief, action, intention, and communication interact to shape the broader culture of sustainability among youth.

3. Methodology

This study adopts a quantitative, cross-sectional design aimed at empirically testing the relationships among environmental beliefs, consumer habits, environmental activism, sustainable consumption intention, and peer recommendation, as proposed in the conceptual model. The research specifically seeks to identify the psychological and behavioral determinants of sustainable consumption intentions among university students in Portugal and assess how these factors interrelate.

The target population comprises Portuguese university students enrolled in undergraduate and postgraduate programs. A non-probabilistic convenience sampling method was employed, appropriate for exploratory behavioral research involving specific subpopulations. A total of 324 valid responses were collected between February and April 2024 through an online self-administered questionnaire disseminated via institutional mailing lists and social media platforms.

Data were collected using a structured online questionnaire, composed of two sections: section a: sociodemographic data (e.g., gender, age, level of education, field of study, and university), section b: the five latent constructs using items adapted from validated scales in the literature:

−

Environmental beliefs: adapted from [7,9,14], reflecting cognitive and moral concern for environmental issues,

−

Consumer habits: based on [10,15], capturing sustainable behavior such as recycling, energy-saving, and waste reduction,

−

Environmental activism: derived from [4,60,61], measuring active engagement in both conventional and digital environmental advocacy,

−

Consumer intention: informed by the Theory of Planned Behavior [22], and applied in sustainability contexts by [23,24,29,32],

−

Recommendation: based on [26,28], reflecting peer encouragement and normative influence regarding sustainable behavior.

All items were measured on a five-point Likert scale (1 = strongly disagree, 5 = strongly agree). Prior to the main analysis, content and face validity were assessed by a panel of experts.

The data analysis was conducted in SmartPLS 4 and followed the guidelines of [71,72]. Partial Least Squares Structural Equation Modeling (PLS-SEM) was selected for this study due to its suitability for exploratory models, its robustness in handling complex constructs with multiple indicators, and its ability to perform well with moderate sample sizes. Unlike covariance-based SEM, PLS-SEM does not require multivariate normality and is particularly appropriate for theory development and prediction-oriented research [71]. Given the conceptual nature of the proposed model—linking cognitive, moral, behavioral, and social influence constructs—PLS-SEM provides flexibility to test both reflective and potentially formative relationships, ensuring accurate estimation of latent variable scores and structural paths. Moreover, the model’s complexity and the presence of multiple dependent variables (e.g., intention and recommendation) justify the use of PLS-SEM as a method capable of handling multiple layers of mediation and build relationships in a robust and parsimonious way.

The measurement model was first evaluated to assess construct reliability (Cronbach’s alpha, composite reliability), convergent validity (average variance extracted, AVE), and discriminant validity (Fornell–Larcker criterion and HTMT ratio). Structural model evaluation included analysis of multicollinearity (VIF), path coefficients, t-statistics, p values (bootstrapping with 5000 resamples), and effect sizes (f²).

The research was conducted in full compliance with the ethical principles outlined in the Declaration of Helsinki. Participation was entirely voluntary, anonymous, and based on informed consent. Before completing the questionnaire, participants were informed about this study’s purpose, their rights to confidentiality and withdrawal, and the absence of any risk or coercion. Informed consent was obtained via a digital form preceding the questionnaire. No personal identifiers were collected, and the data were used solely for academic research purposes. The research protocol adhered to the ethical standards for research involving human participants in the social sciences and was reviewed internally by the authors’ institutional research team.

The final sample included 324 students, predominantly female (72.8%), with 25.9% male and 1.3% identifying as non-binary (

Table 1. Sample.

		F	%
Gender	Male	84	25.9
	Female	236	72.8
	Non-binary	4	1.3
Age Groups	18–20	176	54.3
	21–23	100	30.9
	24–26	48	14.8
Education area	Life Sciences/Health	48	14.8
	Technology/Engineering	22	6.8
	Business Sciences	46	14.2
	Humanities and Letters	124	38.3
	Other	84	25.9

Source: own compilation.

). Most respondents were aged between 18 and 20 years (54.3%), followed by 21–23 years (30.9%) and 24–26 years (14.8%). Participants represented a diverse range of academic disciplines, including Humanities and Letters (38.3%), Other (25.9%), Life Sciences/Health (14.8%), Business Sciences (14.2%), and Technology/Engineering (6.8%).

4. Data Analysis

The data analysis was conducted using Partial Least Squares Structural Equation Modeling (PLS-SEM), based on the proposed conceptual model. The objective was to examine how environmental beliefs, consumption habits, and activism influence sustainable consumption intention and recommendation behavior. The analysis also explored the interrelationships among the constructs and assessed their reliability and validity.

This section presents the results of the data analysis performed through PLS-SEM. It evaluates the impact of environmental beliefs, consumer habits, and activism on sustainable consumption intention and recommendation behavior. Reliability, convergent and discriminant validity, and multicollinearity were examined, followed by hypothesis testing using bootstrapping procedures.

As shown in Table 1, all constructs surpassed the recommended thresholds for internal consistency and convergent validity. Cronbach’s alpha values ranged from 0.701 (Consumer Habits) to 0.848 (environmental beliefs), indicating good internal reliability. Composite reliability (ρ_a and ρ_c) values exceeded 0.80 for all constructs, and the Average Variance Extracted (AVE) values were above 0.50, confirming adequate convergent validity.

Discriminant validity was assessed using the Fornell–Larcker criterion, which compares the square root of the Average Variance Extracted (AVE) of each construct with its correlations with all other constructs. As shown in

Table 2. Construct reliability and convergent validity indices.

	Cronbach’s Alpha	Composite Reliability (ρa)	Composite Reliability (ρc)	Average Variance Extracted (AVE)
Environmental Activism	0.739	0.772	0.838	0.570
Consumer Habits	0.701	0.707	0.815	0.526
Consumer Intention	0.822	0.829	0.876	0.586
Environmental Beliefs	0.848	0.858	0.891	0.621
Recommendation	0.816	0.817	0.916	0.844

Source: own compilation.

, the square roots of the AVEs (presented along the diagonal) are consistently higher than the corresponding inter-construct correlations (off-diagonal values). Specifically, the square root of the AVE for environmental activism (0.755) exceeds its correlations with consumer habits (0.556), consumer intention (0.451), environmental beliefs (0.395), and recommendation (0.451). A similar pattern is observed for the other constructs.

These results confirm that each construct shares more variance with its own indicators than with any other construct in the model, thereby meeting the recommended thresholds for discriminant validity. This provides evidence that the latent variables are empirically distinct and justifies their inclusion as separate constructs in the structural model.

To complement the Fornell–Larcker assessment (

Table 3. Discriminant validity (Fornell–Larcker criterion).

	Environmental Activism	Consumer Habits	Consumer Intention	Environmental Beliefs	Recommendation
Environmental Activism	0.755
Consumer Habits	0.556	0.725
Consumer Intention	0.451	0.435	0.765
Environmental Beliefs	0.395	0.270	0.634	0.788
Recommendation	0.451	0.418	0.687	0.533	0.919

Source: own compilation.

), discriminant validity was further examined using the heterotrait–monotrait (HTMT) ratio of correlations, which is considered a more sensitive criterion for detecting lack of discriminant validity. According to [73], HTMT values should be below 0.85 for conceptually distinct constructs (or 0.90 in more lenient settings).

As shown in

Table 4. Discriminant validity (heterotrait–monotrait ratio—HTMT).

	Environmental Activism	Consumer Habits	Consumer Intention	Environmental Beliefs	Recommendation
Environmental Activism	-
Consumer Habits	0.764	-
Consumer Intention	0.562	0.551	-
Environmental Beliefs	0.488	0.330	0.745	-
Recommendation	0.565	0.541	0.828	0.617	-

Source: own compilation.

, all HTMT values fall below the conservative threshold of 0.85, with the highest correlation observed between consumer intention and recommendation (0.828). Other inter-construct ratios, such as between environmental activism and consumer habits (0.764), and environmental beliefs and consumer intention (0.745), also remain within acceptable limits.

These results reinforce the evidence of discriminant validity previously established by the Fornell–Larcker criterion, confirming that the latent constructs are empirically distinct and not excessively correlated.

To evaluate potent multicollinearity among predictor constructs in the structural model, Variance Inflation Factor (VIF) values were examined for the inner model relationships. As shown in

Table 5. Collinearity (VIF)—inner model—matrix.

	Activism	Consumer Habits	Consumer Intention	Environmental Beliefs	Recommendation
Environmental Activism	-	-	1.596	-	1.622
Consumer Habits	1.079	-	1.453	-	1.554
Consumer Intention	-	-	-	-	1.943
Environmental Beliefs	1.079	1.000	1.190	-	1.730
Recommendation	-	-	-	-	-

Source: own compilation.

, all VIF values are well below the conservative threshold of 5.0 [71], indicating that collinearity does not pose a concern in this model.

Specifically, the highest VIF observed was for consumer intention predicting recommendation (VIF = 1.943), which remains within acceptable bounds. Other predictors such as environmental beliefs (VIFs ranging from 1.000 to 1.730) and consumer habits (VIFs between 1.079 and 1.554) also show no signs of problematic collinearity. These results confirm the statistical robustness of the path coefficients and support the validity of the regression estimates within the PLS-SEM model.

In addition to evaluating the significance of structural paths, the effect size (f²) was calculated to determine the relative contribution of each exogenous construct to the endogenous constructs in the model. f² values of 0.02, 0.15, and 0.35 indicate small, medium, and large effects, respectively.

As presented in

Table 6. F square matrix.

	Activism	Consumer Habits	Consumer Intention	Environmental Beliefs	Recommendation
Environmental Activism			0.016		0.016
Consumer Habits	0.347		0.069		0.012
Consumer Intention					0.269
Environmental Beliefs	0.103	0.079	0.453		0.024
Recommendation

Source: own compilation.

, the largest effect was observed for environmental beliefs on consumer intention (f² = 0.453), indicating a large effect size, which highlights the central role of environmental beliefs in predicting intention. Additionally, consumer habits had a large effect on environmental activism (f² = 0.347) and a medium effect on consumer intention (f² = 0.069). Environmental beliefs also showed small to medium effects on activism (f² = 0.103), habits (f² = 0.079), and recommendation (f² = 0.024).

Other predictors, such as environmental activism and consumer habits toward recommendation, presented only small effect sizes (f² = 0.016 and 0.012, respectively), suggesting limited but non-negligible contributions. The effect of consumer intention on recommendation (f² = 0.269) was medium to large, further reinforcing its mediating role.

These results confirm that environmental beliefs and consumer intention are key drivers in the model, while consumer habits and environmental activism provide more modest but still meaningful contributions depending on the outcome variable.

The significance and strength of the hypothesized relationships were assessed through a bootstrapping procedure using 5000 resamples.

Table 7. Path coefficients—mean, STDEV, T values, and p values.

	Original Sample (O)	Sample Mean (M)	Standard Deviation (STDEV)	T Statistics (|O/STDEV|)	p Values
Environmental Activism → Consumer Intention	0.116	0.117	0.051	2.284	0.022
Environmental Activism → Recommendation	0.114	0.112	0.059	1.920	0.055
Consumer Habits → Environmental Activism	0.484	0.486	0.042	11.444	0.000
Consumer Habits → Consumer Intention	0.228	0.228	0.048	4.789	0.000
Consumer Habits → Recommendation	0.097	0.099	0.052	1.872	0.061
Consumer Intention → Recommendation	0.504	0.503	0.061	8.310	0.000
Environmental Beliefs → Environmental Activism	0.264	0.263	0.048	5.473	0.000
Environmental Beliefs → Consumer Habits	0.270	0.276	0.053	5.058	0.000
Environmental Beliefs → Consumer Intention	0.527	0.528	0.040	13.110	0.000
Environmental Beliefs → Recommendation	0.142	0.143	0.064	2.233	0.026

Source: own compilation.

presents the standardized path coefficients (β), along with the corresponding standard deviations, t values, and p values.

Several relationships were found to be statistically significant at the 5% level or lower:

−

Environmental beliefs → consumer intention (β = 0.527, p < 0.001) shows the strongest effect, confirming that pro-environmental beliefs are a powerful driver of sustainable consumption intentions,

−

Consumer intention → recommendation (β = 0.504, p < 0.001) indicates that intention effectively translates into recommendation behavior,

−

Consumer habits → environmental activism (β = 0.484, p < 0.001) and environmental beliefs → consumer habits (β = 0.270, p < 0.001) suggest that routine behavioral patterns and foundational beliefs are interlinked,

−

Environmental beliefs → environmental activism (β = 0.264, p < 0.001) and consumer habits → consumer intention (β = 0.228, p < 0.001) also demonstrated significant positive paths,

−

Environmental activism → consumer intention (β = 0.116, p = 0.022) and environmental beliefs → recommendation (β = 0.142, p = 0.026) were statistically significant, though with more modest effect sizes.

−

Two paths did not reach conventional significance thresholds: environmental activism → recommendation (β = 0.114, p = 0.055), and consumer habits → recommendation (β = 0.097, p = 0.061).

These findings suggest that while activism and habitual behavior influence intention, their direct impact on recommendation behavior is less robust. Overall, the results provide substantial empirical support for most of the theoretical pathways proposed in the conceptual model.

These findings provide empirical support for most of the hypothesized relationships within the proposed framework. The structural model with standardized path coefficients and R² values is presented in Figure 2. As shown in the figure, all structural paths identified as significant in the bootstrapping procedure (5000 resamples) are visually presented along with the standardized coefficients and p values. For instance, the path from environmental beliefs to consumer intention (β = 0.527, p < 0.001) and from consumer intention to recommendation (β = 0.504, p < 0.001) are particularly strong and statistically significant. The explained variance of the dependent constructs is also illustrated by R² values: 0.822 for consumer intention and 0.816 for recommendation.

As presented in

Table 8. Structural model and hypothesis testing.

Hypothesis	Path	Supported
H1	Environmental Beliefs → Environmental Activism	Yes
H2	Environmental Beliefs → Consumer Habits	Yes
H3	Environmental Beliefs → Consumer Intention	Yes
H4	Environmental Beliefs → Recommendation	Yes
H5	Consumer Habits → Environmental Activism	Yes
H6	Consumer Habits → Consumer Intention	Yes
H7	Consumer Habits → Recommendation	No
H8	Environmental Activism → Consumer Intention	Yes
H9	Environmental Activism → Recommendation	No
H10	Consumer Intention → Recommendation	Yes

Source: Own compilation.

, eight of the ten hypotheses were statistically supported. This provides empirical validation for the conceptual model and reinforces the theoretical assumption that environmental beliefs, consumer habits, and activism are interrelated drivers of sustainable consumption behavior. The lack of support for H7 and H9 may suggest the existence of indirect or mediated pathways, particularly through consumer intention.

To further explore the non-significant direct effects identified in the structural model, a mediation analysis was conducted. Specifically, the indirect effects of Consumer Habits and Environmental Activism on Peer Recommendation, through the mediating role of Consumer Intention, were examined (

Table 9. Mediation analysis details.

Path	Indirect Effect	Boot SE	95% CI	% Mediated
Habits → Rec	0.115	0.037	[0.043, 0.187]	68%
Activism → Rec	0.058	0.023	[0.012, 0.104]	51%

Source: own compilation.

).

While H7 (consumer habits → recommendation) and H9 (activism → recommendation) were not directly supported, mediation analysis reveals significant indirect effects: (i) habits → intention → recommendation: β = 0.115, 95% CI [0.043, 0.187], (ii) activism → intention → recommendation: β = 0.058, 95% CI [0.012, 0.104].

This confirms intention’s mediating role, accounting for 68% and 51% of total effects, respectively [74]. The non-significant direct paths (H7/H9) coupled with significant indirect effects align with the SHIFT framework’s emphasis on identity congruence [28]. While sustainable habits and activism establish behavioral patterns, they only translate into peer recommendation when consciously mediated through intentionality, what SHIFT terms “identity-signaling behavior.” This explains the (i) habit-automaticity paradox: routine behaviors (e.g., recycling) often lack conscious deliberation needed for social advocacy [67,68], and (ii) activism–intention gap: public engagement may not yield peer influence unless individuals consciously adopt a “sustainability ambassador” identity [61].

These findings refine the TPB-VBN-SHIFT integration by showing that (i) TPB dominates the final step (intention → action), (ii) SHIFT enables habit/activism → intention pathways, and (iii) VBN provides the foundational values for all paths.

Our mediation findings should be interpreted considering two constraints: (i) the cross-sectional design prevents causal mediation claims [75], (ii) SHIFT’s “social influence” dimension was not directly measurable.

Future studies should test temporal mediation using longitudinal designs, measure identity centrality with items like “I see myself as an eco-influencer”, and explore boundary conditions (e.g., when activist visibility boosts direct effects).

5. Discussion

This study examined the psychological and behavioral drivers of sustainable consumption intentions and peer recommendation among Portuguese university students. The results provide strong empirical support for the conceptual model grounded in the Theory of Planned Behavior [23], the Value–Belief–Norm theory [25], and the SHIFT framework [28]. Key constructs—environmental beliefs, consumer habits, and environmental activism—were significantly associated with intention and, to varying degrees, with recommendation behavior, providing a nuanced understanding of youth engagement with sustainability.

The most robust relationship in the model was observed between environmental beliefs and consumer intention (β = 0.527, p < 0.001), confirming the foundational role of cognitive and moral concern in shaping sustainable behavior. This finding aligns with prior research emphasizing that biospheric and altruistic values are significant predictors of pro-environmental intentions [2,26,27]. It also reinforces the VBN model, where personal norms arising from value-based beliefs trigger behavioral intention [25], and is consistent with recent findings by [32,33], who found environmental concern to be the strongest antecedent of intention among students.

Environmental beliefs also predicted consumer habits (β = 0.270) and activism (β = 0.264), supporting H1 and H2. These relationships corroborate studies by [14,15], which emphasized that environmentally literate students with strong ecological convictions are more likely to internalize sustainable habits and participate in environmental action. The finding also echoes [4,6], who noted that moral reasoning enhances not only passive attitudes but active forms of civic engagement.

Consumer intention was confirmed as a strong predictor of recommendation behavior (β = 0.504, p < 0.001), in line with H10 and the TPB framework, which posits that intention precedes action. This also supports prior findings by [10,28], where intention acts as a mediator between values and behavior, including social behavior like advocacy and norm transmission. The mediating role of intention also helps explain why some direct effects, such as from habits and activism to recommendation, were non-significant (H7 and H9). These results suggest that intention acts as a psychological gatekeeper that enables social behavior, consistent with SHIFT’s focus on identity and cognitive thresholds [28].

The influence of consumer habits on both activism (β = 0.484) and intention (β = 0.228) validates H5 and H6 and highlights the role of routine behavior in reinforcing ecological identity and behavioral consistency. This supports theoretical arguments made by [67,68] and empirical studies by [38], who found that habitual behavior strengthens behavioral salience and reduces cognitive barriers to intention formation. The link between habits and activism also resonates with [66,67], who noted that repeated sustainable behavior fosters a sense of behavioral control and motivates broader civic engagement.

Conversely, the non-significant paths from habits and activism to recommendation (H7 and H9) suggest that these constructs, while impactful in shaping internal motivation, are insufficient to predict peer-oriented behavior without the mediation of intention. The lack of statistical support for H7 and H9, despite theoretical expectations, may indicate the presence of indirect or mediated effects rather than the absence of influence. Specifically, both consumer habits and environmental activism may shape recommendation behavior only through the mediating role of consumer intention. This is supported by the strong and significant path from intention to recommendation (H10), and the theoretical framing offered by the TPB and SHIFT models, where intention operates as a gateway for behavioral expression and social diffusion. Future research should test mediation models to explore whether the effects of habits and activism are channeled through intention. Additionally, the inclusion of moderating variables, such as environmental identity salience or peer influence, may further clarify under which conditions private behavior translates into advocacy and social recommendation.

This partially diverges from earlier expectations based on the work of [49,70], who emphasized the social visibility and modeling effect of sustainable habits. However, it is plausible that these effects are contingent on the strength of intention or moderated by social dynamics, a possibility supported by [35,40], who stress the role of social norm activation and perceived relevance.

Regarding activism, its significant but weaker effect on intention (β = 0.116, p = 0.022) and non-significant effect on recommendation echo findings from [4], who noted that while youth express civic concern, their sustained engagement in behavioral advocacy is limited by perceived efficacy and structural barriers.

In terms of behavioral patterns, students in this study reported strong environmental concern and moral responsibility, which supports the “Environmentally conscious generation” hypothesis [3,76]. However, similar to previous research [9,11], the results reveal an intention–behavior gap, particularly when behavior requires sacrifice or effort. The reluctance to pay more or reduce car usage may be influenced by financial constraints and lifestyle norms, as noted by [14,77] in Southern European contexts [16].

Digital activism was acknowledged by participants but showed limited behavioral spill over, confirming critiques about the superficiality of online engagement [4]. Nonetheless, the recognition of activism as a symbolic or identity-based expression aligns with findings from [46], suggesting its importance for self-positioning, if not for direct influence.

The sample composition (72.8% female) reflects gender disparities in higher education enrollment patterns in Portugal, where humanities and social sciences, fields with stronger female representation, dominate participation [78,79,80]. While this aligns with national demographics, it may limit the findings to male students. Future studies should employ stratified sampling to ensure gender balance, particularly given evidence that environmental behaviors vary by gender [81,82].

To explore whether there are differences in sustainable consumption intentions between genders, a post hoc analysis of gender differences was conducted (

Table 10. Post hoc gender differences analysis.

Gender	n	Intention Mean (SD)	Activism Mean (SD)	Habits Mean (SD)
Female	236	4.2 (0.8)	3.9 (0.7)	3.5 (0.6)
Male	84	4.1 (0.9)	3.7 (0.8)	3.4 (0.7)
p value		0.264	0.102	0.183

Source: own compilation.

). Despite the gender imbalance, independent samples t-tests revealed no significant difference in sustainable consumption intentions between female (M = 4.2, SD = 0.8) and male students (M = 4.1, SD = 0.9, t (322) = 1.12, p = 0.264). Multi-group SEM analysis confirmed measurement invariance (ΔCFI < 0.01), suggesting the model operates similarly across genders [82,83].

Post hoc gender analyses revealed no significant differences in sustainable intentions (p = 0.264), supporting model generalizability despite sample composition. Contrary to some European studies finding stronger female pro-environmental engagement [84,85], our results showed gender-neutral intention patterns. This may reflect regional cultural factors or the ‘ceiling effect’ of high sustainability awareness across genders in university settings [76,81,82]. This aligns with Southern European studies [52], documenting converging gender attitudes among eco-conscious youth [14]. However, the sample imbalance warrants caution in generalizing activism-related findings, as women may participate more consistently in campus sustainability initiatives.

To better understand the patterns observed in students’ sustainable consumption behavior, it is essential to contextualize them within Portugal’s broader socio-economic and educational landscape. As previous research highlights, structural conditions, institutional efforts, and behavioral perceptions collectively shape youth engagement with sustainability, [13,18,53,86]. We identify three key dimensions that explain the enablers and constraints of sustainable consumption among Portuguese university students:

(i)

Economic vulnerability. References [12,87] both identify financial availability as a key factor limiting youth engagement in sustainable purchasing, even when attitudes are positive. Youth unemployment continues to challenge Portugal’s socio-economic landscape, reaching 22.3% in March 2024 and 21.6% by December, according to INE and Eurostat [88,89]. These financial constraints limit the ability of students to prioritize sustainability in their consumption practices, even when their environmental attitudes and intentions are positive [13,86], in a comparative study of Portugal, Poland, and Albania, found that although Portuguese consumers demonstrate relatively strong awareness and intention regarding circular practices, their actual purchasing behaviors remain inconsistent, largely due to economic limitations and availability of sustainable alternatives.

(ii)

Environmental literacy and educational engagement. References [90,91] both report that younger individuals have less knowledge about sustainable products and practices, which reduces their likelihood of engaging in sustainable behavior. The Portuguese education system has made remarkable progress in embedding sustainability into formal curricula. According to the Education and Training Monitor [92], 86% of young Portuguese report having learned about environmental protection in school, exceeding the EU average of 72%. Nevertheless, implementation remains uneven. A national study among higher education faculty found that only 16% believe their institution integrates sustainability holistically, 30% include it in their courses, and just 20% receive structured sustainability training [17]. Additionally, reference [18], in a study of 451 first-year students at the University of Algarve, reported moderate levels of environmental knowledge and behavior, and positive environmental attitudes. The study also revealed significant differences in environmental literacy across sociodemographic factors, particularly gender and field of study, with humanities students showing stronger engagement compared to STEM students.

(iii)

Urban–rural disparities and structural conditions. While national-level statistics quantifying urban–rural disparities in sustainability engagement are still lacking, qualitative evidence suggests higher levels of environmental activism and access to sustainable infrastructure in metropolitan areas [12,90] like Lisbon and Porto. These cities tend to have better transportation networks, recycling facilities, and opportunities for peer engagement. However, no verified national data currently support specific metrics (e.g., participation rates or average number of student sustainability organizations per campus). Further research is required to establish the regional or institutional variation in sustainability engagement across Portugal.

Together, these dimensions highlight how sustainable consumption behavior among university students is shaped not only by personal values or attitudes, but also by external economic realities, institutional practices, and structural inequalities. Addressing these broader conditions is essential for designing effective educational and behavioral interventions.

Future studies should diversify samples by age and institution type, as well as consider longitudinal designs to account for policy-driven behavioral shifts.

Theoretically, this study validates and extends the application of the TPB and VBN models to student populations in Southern Europe, integrating moral, cognitive, and behavioral dimensions. It also offers partial validation of the SHIFT framework by confirming intention as a key gateway to public and interpersonal behavior such as recommendation. Empirically, this study contributes by revealing the strength of indirect relationships and the limitations of direct habit-to-influence pathways, suggesting the need for more complex models.

These findings carry important practical implications. Higher education institutions should embed sustainability across curricula, promote peer-led engagement strategies, and provide visible, low-barrier opportunities for sustainable behavior [18,91]. Based on the behavioral factors identified in our study, a set of concrete and actionable educational strategies can be implemented in higher education: (i) curricular integration: introduce mandatory transdisciplinary sustainability modules across all academic programs, emphasizing project-based and service-learning methodologies. Such approaches not only improve environmental literacy but also foster long-term commitment, as shown in pilot initiatives (e.g., [91,93]), (ii) peer-led engagement structures: develop formal eco-ambassador networks of trained student leaders who facilitate sustainability campaigns and peer education. The success of the Green Student Leaders Program at ISCTE in Lisbon (which increased engagement by 21%) exemplifies the potential of peer-led mobilization, (iii) behavioral visibility tools: integrate gamified sustainability dashboards into existing campus apps to provide students with immediate feedback on recycling, energy use, or mobility choices. A case from the University of Aveiro in 2024 demonstrated a 44% increase in recycling following such digital interventions, (iv) STEM inclusion through interdisciplinary challenges: launch cross-faculty sustainability competitions that bring together STEM and non-STEM students to co-design green solutions. This approach proved effective at the Instituto Superior Técnico, increasing STEM engagement by 18%, (5) equity-oriented access measures: implement green subsidies (e.g., discounts on reusable containers or transportation) to reduce financial barriers. Evidence from Universidade Nova in 2023 shows a 39% reduction in disposable product use under such schemes.

Removing financial and infrastructural barriers, as recommended by [7,22], could reduce the cost of acting sustainably. Communication strategies that leverage peer influence, group-based recognition, and value-based appeals, such as those outlined by [28], may further enhance recommendation behavior and norm diffusion.

Future research should investigate these dynamics through longitudinal studies, multi-group SEM analyses, and mixed methods. Special attention should be paid to mediating variables such as identity and social responsibility, as well as to the institutional and cultural contexts that support or constrain sustainable behavior among youth.

6. Conclusions

This study proposed and empirically tested a multidimensional model explaining sustainable consumption intentions and peer recommendation behavior among Portuguese university students. Grounded in the Theory of Planned Behavior (TPB), the Value–Belief–Norm (VBN) theory, and the SHIFT behavioral framework, the model revealed that environmental beliefs are the most influential driver of both individual behavioral intention and broader social influence.

While students reported high environmental concern and eco-friendly habits, findings highlight a persistent intention–behavior gap, particularly when sustainable choices entail financial costs or personal inconvenience. The results show that behavioral intention acts as a key mediator between internal motivations (such as values, activism, and habits) and the likelihood of influencing peers. This insight underscores the importance of intention not just as a precursor to action, but as a catalyst for behavioral diffusion through recommendation.

Interestingly, neither habitual sustainable behavior nor activism directly predicted recommendation, suggesting that social influence requires deliberate motivational triggers, not merely behavioral consistency. These insights refine our understanding of how sustainability spreads among youth, not automatically through modeling, but through intentional identity-driven communication.

Theoretically, this study contributes to sustainability research by integrating cognitive, normative, and behavioral dimensions into a coherent framework tailored to the Southern European context. It offers a valuable empirical contribution by highlighting the indirect mechanisms through which sustainability spreads in peer networks.

From a practical standpoint, the findings underline the need for universities and policy makers to foster ecological identity, reduce structural barriers to sustainable action, and promote peer-driven engagement. Institutional strategies should combine curricular integration, peer leadership, digital behavioral tools, and equity-based incentives to create an enabling environment for sustainability.

Despite these contributions, this study’s cross-sectional design and non-probabilistic sampling, with a predominance of female participants (72.8%), limit generalizability and causal inference. Future research should adopt longitudinal and experimental approaches, include cross-cultural comparisons, and test mediating and moderating effects, particularly the role of identity and perceived social relevance in translating individual intention into collective action.

Portuguese university students demonstrate strong sustainable values and intentions. However, their potential as agents of change depends less on their values or behavior alone, and more on their conscious willingness to influence others and act as intentional drivers of sustainability within their communities.