Sugar intake is increasing globally due to changing diets, such as increased availability of sweet, processed foods [1
]. A review of nationally representative surveys from 16 countries found adults consumed 13.5%–24.6% of their total energy from added sugar, which is far above the WHO recommended sugar intake level of 5%–10% of energy intake (approximately 12 teaspoons) per day [2
]. A systematic review conducted by Te Morenga et al. [4
] reported that increased body weight is associated with increased consumption of free sugars, with particularly strong links to sugar-sweetened beverage consumption.
Increasing added sugar in diets is one factor associated with a corresponding increase in body weight in adults [4
]. By 2025, 18% of adult men and 21% of adult women worldwide are expected to be obese (have a body mass index (BMI) greater than 30.0 kg·m−2
]. In addition, the economic impact is significant as medical costs in the US were 36%–100% higher for obese populations than those with BMI in the healthy range [6
]. Excessive sugar consumption is one of the public health issues that needs to be addressed through a range of different measures.
In Ayurvedic medicine (an Indian traditional health care system), the leaves of a large vine, gymnema sylvestre
, are used to treat diabetes and dental caries, reducing obesity and inflammation [7
]. Gymnema sylvestre
has been reported to exhibit anti-diabetic properties as several constituents (gymnemic acids, gurmarin and gymnemasaponin V) act together to normalize blood sugar levels by decreasing plasma glucose and increasing insulin secretion by the pancreas and regeneration of pancreatic islet cells [7
]. It has been found that chewing the leaves or brewing it as tea results in a temporary, reversible sweetness inhibitor [9
]. This taste modulation has given gymnema sylvestre
the reputation of being a “sugar destroyer” or “gurmar” in Hindi [7
]. More recently, the active components from gymnema sylvestre
have been identified and purified. Analysis of these components found sweetness suppression activity in humans was affected by a group of triterpene saponins called gymnemic acids [12
]. In humans, gymnemic acids selectively suppress taste responses to sweet compounds without affecting the perception of other taste elements (salty, sour, bitter and umami) [14
]. Sweet tastes are sensed by T1Rs (type 1 taste receptors), a group of G-coupled protein receptors found in taste bud cells and parts of the peripheral gastrointestinal tract [15
]. Gymnemic acids are structurally similar to glucose molecules, and due to its anti-sweetness properties, acts as an antagonist and inhibitor of the T1R unit to produce the temporary suppression of the perception of sweet taste [10
]. Further research is clearly needed to understand the effects of gymnema sylvestre
and to consider its effectiveness as a potential tool against high global added sugar consumption and its effects.
Gymnema has traditionally been prepared as a tea beverage either to be drunk or used as a mouth rinse [10
]. Questions had previously been raised about whether the glucose-suppressing effects would persist after the leaves underwent food processing [9
]; however, advancements in food processing have resulted in the development of several food products containing gymnema including sauces and breath mints [18
]. Recent studies using formulated gymnema-containing products such as a dissolving tablet or “lozenge” found that consumption of gymnema in this form reduces both the intake and pleasantness of confectionary [20
]. In a double-blind crossover study, consumption of a gymnema-containing “lozenge” reduced the desire for further servings of confectionary, in the two minutes prior to eating the next serving of confectionary [20
]. This supported the hypothesis that the desire to consume more high sugar foods was not entirely dependent on the reduction in pleasantness experienced due to taste changes following consumption of the gymnema mint, but rather the reduction in desire was a result of reduced neural feedback to the reward response region of the brain [20
From current evidence it is unclear whether any particular population subgroups would benefit from the anti-sweetness effects of gymnema more than others. For example, if the effect of gymnema may be more pronounced in higher refined sugar consumers or those who have been identified as supertasters. Supertasters (those who have a strong reaction to the bitter compound 6-
(PROP)) have been shown to experience sweet foods more intensely than those who tasted PROP as less bitter (non-tasters or medium tasters) [22
]. Supertasters therefore tend to prefer foods which are less sweet [23
], whereas non-tasters or medium tasters reported a lower intensity of sweetness intensity for both sucrose and added sugars, and had a greater preference for sweet-tasting foods and an increased intake of added sugar [24
]. As the intensity of sweet liking has been linked to increased consumption of these foods [25
], PROP non-tasters or medium tasters may benefit more from using a product that inhibits the perception of sweet taste to reduce their intake.
High BMI is associated with increased consumption of free sugars, as well as decreased perception of sweet taste and an increase in reported liking of high-sugar sweet foods [4
]. To date however, no research has been conducted on the relationship between BMI and frequency of sugar food intake following the consumption of gymnema sylvestre.
Several sensory studies have suggested that men prefer more intense sweet-tasting food than women [28
] and have a higher pleasantness rating when consuming sweet foods [26
]. Conversely, other studies have shown that women are more likely than men to choose high sugar snack foods such as candy or chocolate to provide psychological and physiological comfort [30
]. There are, however, no known studies to date that have explored gender differences in high-sugar sweet food consumption following sweet taste modulation.
The aim of the present study was to examine the effect of a sugar reduction tool (gymnema sylvestre) on the desire for high-sugar sweet food intake in different subgroups (gender, self-identified sweet taste preference, supertaster status and/or varying body composition). Identification of subgroups that may benefit from a product that creates an aversion to sugar-sweetened products by reducing desire and understanding the unique ways in which these groups respond to pleasantness, is important to gain an understanding of who may benefit from this tool.
The primary finding of this study was that gymnema acid-containing mints reduced intake of sugar-sweetened foods. We found that participants ate 0.48 (21.3%) fewer servings of their favourite chocolate after consuming a GS-containing mint compared to placebo. Consumption of the GS mint also resulted in a 22.7% decrease in desire to eat high-sugar sweet foods and 31.0% reduced pleasantness of high-sugar sweet foods eaten but did not affect hunger. Furthermore, those who self-identified as having a “sweet tooth” had a greater reduction in both the pleasantness of eating high-sugar sweet foods and desire to eat more after consuming the GS mint compared to those who do not. There were no significant differences in amount of high-sugar sweet food eaten by BMI groups, gender or PROP taster status.
4.1. Effect on Taste Receptors
The significant reduction in the amount of high-sugar sweet food eaten and the reported pleasantness experienced with eating indicates that the GS mint was effective in inhibiting the T1R2 + T1R3 heterodimer which senses sweet taste on the tongue [33
]. These receptors are activated by sucrose but also other mono- and di-saccharides, sugar alcohols, and other small molecule sweeteners [16
]. Since other taste dimensions are not affected; following suppression of the T1Rs, participants primarily tasted the other components of high-sugar sweet foods, i.e., the high cocoa content in dark chocolate which heightens the bitter taste. This disjunction between the expectation of the chocolate bar based on the label, brand and prior knowledge about how the product should taste does not align with the reality of the experience of the high-sugar sweet food they are eating, and of itself may reduce pleasantness and enjoyment of the product [34
], and is supported by our data.
4.2. GS Mint Reduces Acute Consumption of High-Sugar Sweet Foods (Acute vs Chronic Consumption)
Reduced consumption of high-sugar sweet foods following GS mint intake is consistent with previous findings [20
]. Furthermore, a significant reduction in both pleasantness of high-sugar sweet food and the desire to consume more was found after consuming the GS mint in both the current investigation and Nobel et al. [20
]. The resulting taste changes of high-sugar sweet foods experienced after consuming a gymnema-containing product are not the only contributing factor to this reduction in pleasantness and desire, as it has been reported that even prior to eating high-sugar sweet foods there is decreased activity in the reward response region of the brain following gymnema consumption [35
]. fMRI imaging has shown that following consumption of a gymnema-containing product there was decreased neural recruitment in the areas of the brain associated with reward response (nucleus accumbens, precuneus, OFC, insula and caudate) [35
]. In practice this may mean that consuming a GS mint may reduce ad libitum intake of other high sugar products even prior to the consumption of these products (decreased desire) and if they are eaten, they will not be as enjoyable (reduced pleasantness) to consume due to the sugar-suppression effects. In other words, as consumers will “know” that the GS mint will make the high-sugar sweet food not taste like it normally would, it will reduce their desire for the product (akin to learning effects), and so may subsequently reduce their intake of high-sugar sweet foods (in the longer term).
4.3. Behavioural Aspects of Consuming GS Mints
Consumption of GS products result in a noticeable change in the way food tastes and may result in the perception that the other taste elements (e.g., bitter) are intensified [9
]. This impacts on the enjoyment of high-sugar sweet foods eaten as participants reported a significant decrease (49 ± 2.9 mm vs. 67 ± 2.3 mm; Figure 2
) in perceived pleasantness of eating high-sugar sweet foods following consumption of the GS mint; consistent with previous results wherein pleasantness rating was 22.2/100 mm lower after consuming the gymnema-containing product [20
]. Therefore, consumption of sweet-tasting foods may be impacted following use of a GS-containing product. However, for this approach to be successful, consumers must have sufficient motivation to ingest the GS mint, knowing that it will prevent their enjoyment of high-sugar sweet foods. Consumers aiming to reduce their sugar intake that have reached the ‘preparation’ or ‘action’ stages of the transtheoretical (stages of change) model may find greater success with such an approach to restricting sugar consumption [36
]. If, however, they have not reached these stages, they may not have sufficient motivation to voluntarily take flavour modulation products (e.g., GS mint) [36
]. This is the case for other health behaviours such as smoking which also requires a high level of motivation to promote change, particularly when using interventions that result in temporarily reducing pleasantness and subjective wellbeing for long-term improvement [37
]. Further research needs to be conducted to explore the relationship between motivation level and long-term success at reducing consumption of high-sugar sweet foods using GS mints.
4.4. Effect of the GS Mint on Those with a “Sweet Tooth”
This study found that the effect of the GS mint was more pronounced in those who self-identified as having a “sweet tooth” than those who did not; i.e., GS mint intake led to greater reductions in pleasantness and desire ratings for high-sugar sweet foods in those with a sweet tooth. Reed [38
] describes a “sweet tooth” as someone who prefers sweet foods, however preference for sweet foods may vary over time dependent on a number of modifiers including age, culture, mood, and accessibility. The present study observed that those who have a sweet tooth derived more pleasure from consuming sweet foods than those who do not (Figure 3
). The brain has a strong pleasure response to sweet taste, so pursuit of pleasure and taste preferences are major drivers of sugar consumption [39
]. Therefore, the GS mint may be more effective in reducing sugar intake in those with a self-proclaimed sweet tooth; however, more research, using a longer intervention period, will be required to investigate this assertion.
4.5. Relationship between GS Mint and Gender
In this study we found gender had no effect on the amount of high-sugar sweet food consumed following the consumption of a GS mint. One possible explanation may be an interaction of the competing two factors that women are more likely to choose high sugar foods as a source of comfort [30
], and therefore, on average, consume greater quantities of sugar, whereas men prefer a more intense sweetness than women [28
]. Men reported higher non-significant mean ratings for pleasantness after the consumption of either the GS mint or placebo than women (p
= 0.059). This is consistent with the findings that men report high-sugar sweet foods as more pleasant than women [26
]. It is important to interpret this with caution as there were fewer men in this study (35.7% of participants), and men have been underrepresented in some [9
] but not all [20
] previous investigations on the sugar suppressive effects of gymnema. Overrepresentation of women in these studies may reflect consumer interest.
4.6. Relationship between GS Mint Consumption and BMI
This experiment did not show a relationship between the consumption of the GS mint and BMI groups. Previous findings demonstrated that increased BMI was associated with decreased perception of sweet taste [41
] and increased liking of high-sugar sweet foods [9
]; therefore, suggesting that obese people would consume more high-sugar sweet food after consuming the GS mint. In this study no differences in chocolate consumption, desire or pleasantness were found between overweight/obese participants and normal weight participants. Others have suggested that fat consumption, rather than sugar, may play a larger role in obesity [26
]. This would indicate consumption of gymnema-containing products may benefit those who have difficulty restraining their sugar intake, rather than a specific BMI group, but further studies are needed.
4.7. Relationship between GS Mint Consumption and PROP Taster Status
Current research suggests that PROP tasters (medium tasters and supertasters) perceive bitter and sweet-tasting compounds more intensely than other non-tasters and therefore are less likely to enjoy very sweet foods than non-tasters [28
]. However, other studies have disputed this connection between PROP taster status and sweet food preference [43
]. This study was consistent with the conclusion of the latter, finding no significant relationship between PROP taster status or the amount of a high-sugar sweet food eaten, pleasantness of the high-sugar sweet food nor desire for more. Despite the difference in preferred sweetness intensity, our findings suggest that this sugar reduction tool is unaffected by PROP taste status i.e., no effect of ‘supertaster’ status. However, anecdotally, some participants reported that the GS mint tasted bitter, which may relate to their PROP taster status, hence palatability of the mint may be higher among PROP non and medium tasters. There were more supertasters in this study compared to the 30% non-tasters, 50% tasters, and 20% supertasters distribution in the population [45
]. But this distribution can vary based on gender [46
]—females tend to be supertasters and frequently rated PROP bitterness more intensely compared to males—and ethnicity [48
]. There were more females and Asians in the current study, and this may have contributed to the taster status distribution observed.
4.8. Study Limitations and Future Directions
One surprising finding was that several participants did not follow the expected trend of reduced consumption of high-sugar sweet foods after consumption of the GS mint, and in fact ate more servings despite the same participants giving the high-sugar sweet food low pleasantness ratings. We are speculating that this may be due to a “curiosity factor” as participants were unfamiliar with the sugar suppression effect of gymnema and wanting to experience the effect. We hypothesise that repeated exposure to this product would eliminate this “curiosity factor” as participants become accustomed to the taste modulation.
This study was limited by the single-blinded approach. Participants received the placebo at the first visit and GS mint at the second. Participants were told they would receive two different products and instructed not to discuss the products with other participants due to slight differences in colour and taste of the placebo relative to the GS mint. Due to the distinct taste profile and difference in appearance, a conscious decision was made to provide the known prior to the unknown.
As with previous studies, men were underrepresented in this study. Further work in this area should target recruitment of men to explore any potential gender differences in consumption of sweet foods following intake of the GS mint.
To the best of our knowledge no evidence exists about the effects of long-term (chronic) intake of gymnema-products for its anti-sweetness effects. The expected length of sweet taste suppression for one GS mint is 30 to 60 min (based on manufacturer guidelines). Future research should explore the effects of chronic consumption of gymnema sylvestre products and the impact of consumption on free-living, non-diabetic adults, including whether the GS mint would be effective at altering sugar consumption habits if used whilst having a sugar craving, similar to the use of Nicotine Replacement Therapy to overcome a craving for a cigarette. Future investigations may also provide greater insights into the effect of the GS mint on those who have a “sweet tooth”. Initial results from this study gives evidence that this group may benefit more from the GS mint to control sugar intake as there was a larger decrease in pleasantness rating following consumption. Studies should screen for those who have a sweet tooth among a larger cohort.
It is important to bear in mind the real-world applicability of these products. People generally consume a range of sweet foods, not just chocolate. Future research is needed to determine how much of an impact gymnema-containing products may have on sweet foods consumed outside of a laboratory environment, as consumers’ eating habits vary significantly, and they do not generally consume only one type of sweet food, so having access to a wider variety of sweet foods may alter their perceived pleasantness and desire for more sweet foods. Conducting qualitative research to understand participants’ experiences with gymnema-containing products would provide insight into how these laboratory findings may translate to everyday life and identify any issues surrounding taste, compliance and consumption of non-nutrient-rich sweet foods.