The prevalence rate of overweight or obesity among adults increased 5.3% globally from 2006 to 2016, in which the Western Pacific (6.9%, 24.8~31.7%) and Eastern Mediterranean (6.9%, 42.1–49.0%) regions exhibited the highest increases according to the World Health Organization (WHO) [1
]. Obesity is an issue worthy of study. It is directly related to mortality and chronic diseases such as heart disease, diabetes, hypertension, stroke, sleep apnea, cancers, and metabolism syndrome (MetS) [2
]. However, research indicated that among people attempting to lose weight, uncontrollable eating behaviors and the desire for high-calorie foods greatly reduce the effectiveness and efficiency of treatment programs [3
“Food addiction” (FA) is a new concept that appeared in the last decade. It implies an “uncontrollable eating behavior that often occurs in compulsive overeating” [5
]. Unlike bulimia nervosa, people with an FA who compulsively overeat do not compensate for their binge eating behavior by purging, nor do they assuage the guilty feelings of overeating by other efforts [7
]. In addition to overeating, people with an FA may also be continually eating, even if the amount eaten is small [6
]. Emotional overeating is significantly associated with overeating, eating disorders, and depression [8
A growing body of research has found that excessive eating and compulsive eating behaviors are associated with a strong preference for certain foods, such as high-sugar, high-fat, and high-salt foods [5
]. This behavior is similar to drug and alcohol addiction, and many studies have shown that such foods are the same as addictive drugs and alcohol, in that they can interfere with the reward mechanism of the brain’s limbic system [9
]. The reward pathway involves dopamine, opioids, and cannabinoids, which when overexposed, can result in neurological adaptation, leading to continuing forced intake and over-intake in order to reach the same level of reward. This eventually causes dependence and cravings [9
]. Studies also pointed out that removing such substances can lead to negative emotions and activation of the stress system, including the hypothalamic-pituitary-adrenal (HPA) axis [13
], which urges individuals to get relief from negative emotions or bring about happy emotions through eating rewards [14
Studies have pointed out that stress is an important cause of the development of addictive behaviors and the inability to quit such behaviors [15
]. The degree of psychological and social stress experienced by individuals and the number of stressors in life are highly correlated with overeating and unhealthy eating patterns, such as a low intake of vegetables and increased intake of high-calorie foods [16
]. Stress has been identified as a response to an event or an ongoing sense of worry [18
]. Therefore, the degree of perceived stress is a highly personalized feeling that varies among people depending on individual vulnerability and resilience [19
]. The “fight or flight response” can be stimulated by high activation of the autonomic nervous system when encountering stress [19
]. In this condition, people often experience anxiety and rejection, and tend to avoid conflicts or manipulate tensions [19
]. The reward feeling obtained by palatable food and eating behaviors can be seen as a representation of the flight response. For this reason, even in the absence of hunger or calorie needs, individuals may overeat [20
With the increasing rate of overweight and obesity, the WHO classifying stress as the health epidemic of the 21st century [21
], and the above-described evidence, we hypothesized that increased degree of perceived stress has become a worthwhile factor affecting the progressive obesity of a population, and FA may play a role as an intermediate factor. Due to the lack of investigations on the rate of food addiction among the general population, and Asia exhibiting one of the highest increasing overweight or obesity rate among adults in WHO data, the purposes of this study were to (1) investigate the prevalence of FA in Taiwan, (2) understand correlations among perceived stress, FA, and the body mass index (BMI), and (3) determine the potential mediating effect of FA due to perceived stress on BMI.
Our aim in this study was to examine interrelationships among perceived stress, FA, and BMI. Whether FA acts as a mediator in the relationship between perceived stress and an increased BMI in young adults was also a main concern.
Our results showed that perceived stress during the past month was positively correlated with BMI. However, a study of 5077 Hispanic/Latino adults indicated no associations between perceived stress in the past month and being overweight or with obesity [27
]. A five-year longitudinal study in Australia demonstrated that although perceived stress in the past month was not associated with BMI, it was significantly associated with life health behaviors such as daily energy intake and physical activity [28
]; therefore, as long as a perception of stress persists, it is highly likely to increase the risk of obesity. Additionally, research also showed stronger associations between perceived stress and weight gain in participants who were normal weight, overweight, or younger [28
], which may explain why we found significant such relationships in our sample (an average age of 26.96 years and a mean BMI in the normal range) while others did not.
In terms of long-term stress, a prospective study of adults in Australia showed that people who had three or more stressors in the past year had significantly higher weight gains than those who did not [28
]. The number of chronic stressors had a higher obesity OR and was significantly associated with the waist circumference and body fat percentage; in heavier-weight groups, more chronic stressors were carried [27
]. The evidence of higher perceived stress producing a greater BMI was reiterated.
As to the relation between perceived stress and FA, this study showed that the higher the perceived stress score, the higher the odds of FA. This result is consistent with several studies. A French study of 1349 college students showed that psychological distress from perceived stress, anxiety, and depression was significantly positively correlated with the number of FA symptoms [29
]. A study among 408 type 2 diabetic patients indicated that subjects with higher symptom counts of FA reported a higher degree of stress [30
]. Research has pointed out that stress tolerance was significantly negatively correlated with emotional eating, exogenous eating, uncontrolled eating, and FA [31
In stress-related diseases, FA was positively correlated with post-traumatic stress disorder (PTSD). In addition to the indication that the prevalence of FA increased with the symptom count of PTSD, a study of 49,408 female nurses showed that those who had the highest number of PTSD symptoms (six or seven symptoms) had more than twice the FA rate compared to those without PTSD symptoms or a traumatic history [32
In terms of sex differences, this study was similar to other studies in that women had a higher level of perceived stress than men [27
], and had a higher rate of FA [33
] or eating disorders [34
]. One study pointed out that the proportion of FA and the number of symptoms in women aged 18~34, 35~54, and over 55 years were significantly higher than men in the same age groups, and there was no significant difference among the groups [35
However, another study showed that although women had significantly higher negative emotional effects (especially anxiety and perceived stress) than men, emotional eating and FA symptoms, after adjusting for anxiety and perceived stress, a sex difference only occurred for the emotional eating score but not on the FA symptom counts. On this basis, that study believed that a true sex difference lies in the emotion-driven eating behavior rather than clinical addiction symptoms like disordered eating behaviors [29
]. Inconsistent with our findings, after adjusting for sociodemographic variables of perceived stress, age, employment status, and educational attainment, the odds of FA for females was still significantly higher than that of men. Under the same PSS, the difference may have been caused by the use of a simpler modified YFAS of that study, different adjusted variables, or the effects of European and Asian ethnicities and cultures.
Our results showed a positive relation between FA and BMI, which is consistent with other research [4
]. Individuals who were overweight or with obesity had a higher relative risk of FA than those who were normal or underweight according to either BMI or body fat percentage measurement [33
]. A study using neuroanatomy to examine relationships among brain structure, FA, and BMI showed that a higher BMI predicted a significantly lower thicknesses of the (pre)frontal, temporal, and occipital cortices and an increased volume of left nucleus accumbens [37
]. The former is believed to be related to the ability to regulate or suppress emotions and self-control, while the latter is considered to play an important role in rewards, happiness, laughter, addiction, aggression, fear, and placebo effects [38
]. Although the study claimed that symptoms of FA did not account for the major part of the structural brain variances associated with BMI in the general population, it may still explain additional structural differences in the orbitofrontal cortex, a hub area of the reward network [37
As we hypothesized, the present study identified a positive path effect of perceived stress to FA and then to BMI. FA is a mediator of perceived stress that affects BMI. To our best knowledge, there is only one other study that examined the path of these three. Despite the study also showing a mediating role of FA and higher psychological distress being indirectly related to an increase in weight via addictive-like eating symptoms, that study found a negative association between psychological distress and weight that did not reach statistical significance [29
]. It was explained as having an unexpected suppressive effect on the statistical analysis [29
]. Therefore, we believe a conclusion of proper stress management and screening for FA that would benefit the population seeking to lose weight can still be made.
Since the degree of perceived stress varies in individuals, understanding characteristics of people who have less stress tolerance and are highly reactive to stress is important [39
]. Research has shown that individuals with high impulsivity levels are more likely to result in obesity [40
], and activities such as exercise, music, and meditation can help sooth emotions and avoid overeating [43
]. Although the content of FA has been debated over whether it is more of a “substance addiction” or a “behavior addiction” [43
], pharmacologic therapy and cognitive behavioral therapy are both believed to be effective ways to treat substance addiction and addictive behaviors, and were proven to elevate the efficiency when both therapies were applied as treatment [45
The strengths of the study was its large sample size in Taiwanese young adults and that it is the first study to examine interrelationships among perceived stress, FA, and BMI with Asian criteria of BMI. Moreover, it provides the prevalence rate of FA in a general young adult population, which is also not yet fully discussed in the literature. However, there were significantly more female participants than male participants in our sample. Since we found a sex difference among the odds of FA, the prevalence rate of FA in the general population may be lower than 12.98% in our overall population. Further investigation from the angle of sex differences may provide valuable insights. The limitation of the study was its cross-sectional design. In spite of the statistical method used to analyze the pathway, a longitudinal study is still needed to support a firm causal relation from perceived stress and FA to BMI. Another limitation that is worth mentioning is that there may be selection biases in those who completed the online study (i.e., those with access to internet, computer, social media) that might limit the generalizability of the findings.