With most of the world now living in countries where the prevalence of death is higher in those overweight than underweight, it strikes the question of why people are obese?
For example, the global obesity incidence has now more than doubled since 1980 (Fox, Feng, & Asal, 2019).
As weight-loss experts here at Plato Weight Management, we are asked all the time by our clients undertaking our weight management program whether weight gain is solely down to a lack of discipline and motivation.
Therefore, in this article, we’ll be breaking down five causes of obesity, including:
- Depression
- Stress
- The built environment
- Physical inactivity
- Genetics
Depression
Unfortunately, depression is hugely prevalent in the obese population today and is a reason why people are obese.
For example, Blaine (2008), which included 33,000 participants, found that depressed people were more likely to be obese than non-depressed people.
Additionally, a study by Murphy et al. (2009) showed a five times higher chance of depressed, obese individuals gaining weight than non-obese. So, there seems to be a consensus in the research that supports the premise that weight gain contributes to depression.
However, depression has been indicated to not just a consequence of obesity, but a cause too. Woo, Seo, McIntyre and Bahk (2016) indicate a two-way link between depressive disorders and obesity, while Luppino et al. (2010) showed that depression is foretelling an individual becoming obese.
Interestingly, Luppino and colleagues suggest that since obesity can be considered a state of inflammation due to the proinflammatory effects of fat tissue and inflammation has been linked with depression, inflammation may actually be the connection between both conditions.
In comparison, an epidemiological study by Miller and Raison (2016) on a large community sample also found that increased inflammation could predict a future prognosis of depression.
Therefore, not only is depression a cause contributing to obesity but a consequence stemming from obesity too, which could come from inflammation as a source.
Stress
Additionally, chronic stress is a reason why people are obese today.
A meta-analysis by Chida, Gibson, Whitaker and Steptoe (2012) found that stress indicates weight gain.
When individuals are confronted with chronic stressful circumstances (stress occurring daily), they consume highly caloric foods in response. If this stress results in a caloric surplus daily, then it could lead to weight gain and eventually obesity (Torres & Nowson, 2007).
Congruently, it has been suggested by both human and animal studies that chronic stress enhances the consumption of high caloric foods and subsequently the onset of visceral obesity (Elder et al., 2011).
This shows a general agreement between studies that chronic stress can play a role in obesity.
Alternatively, Adam and Epel (2007) propose that the relationship between stress and eating may be mediated by the interactivity of the hypothalamic-pituitary–adrenal (HPA) axis and the reward centre of the brain.
However, human studies have proved more challenging in producing evidence than animal models have regarded the connection between the HPA axis, stress, and metabolic diseases as humans have been found to have more understated changes in the HPA axis (Bose, Oliván, & Laferrère, 2010).
This evidence implies that abnormal interactions between the HPA axis and the brain’s reward circuitry may be an element contributing to obesity. Still, more research needs to be done to understand its effect in humans fully.
Accordingly, obesity may be partly due to the excessive eating of calorie-dense foods due to malfunctioning brain intercommunication from chronic stress.
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The built environment
Also, the built environment (a person’s surroundings that are human‐made or altered) in which a person lives is a reason why people are obese.
There is now extensive literature on urbanization towards obesity (Bleich, Cutler, Murray, & Adams, 2008).
However, a meta-analysis of 74,168 participants from ages 2-19 revealed that urban children had 74% lesser odds of obesity than urban children (Johnson & Johnson, 2015). In light of this, it can be said that as we age from childhood, the probability of becoming obese from rural environments deviates towards urban environments.
An aspect that could be a key driver towards obesity in adults due to urbanization is food availability. Enhanced availability of fast food establishments has been connected with higher BMI and obesity rates in a study of 10,763 participants conducted in the United States (Morland, Diez Roux, & Wing, 2006).
This is in contrast to a study by Dubowitz et al. (2012), which found that the pervasiveness of supermarkets within the proximity of a person’s home was actually connected with lower BMI.
So, food availability may be beneficial for some people while dieting while others not.
Moreover, Blanck et al. (2012) note that parks are an effective obesity prevention strategy as they provide an opportunity to exercise for children and adults.
Gordon-Larsen, Nelson, Page and Popkin (2006) verify this as they found that children with access to more parks were less likely to be overweight.
So this gives an example of the importance of parks for obesity prevention.
Therefore, the discrepancy between children and adults may suggest that the environmental aspects and the effect of these aspects contributing to obesity between urban and rural areas may diverge as children age and that urban areas can present positive consequences of food availability in addition to negative consequences.
Genetics
Genetics may also be a reason why people become obese.
A recent Norwegian study has identified that genetically susceptible individuals have a higher likelihood than non-genetically susceptible individuals of obtaining a higher BMI (Brandkvist et al., 2001).
Also, the study proposes that genetic predisposition may have related to the obesogenic environment to ensue in a higher BMI in recent decades.
At the same time, genetic factors contributing to obesity are further exemplified by a UK study in 2008, which consisted of 5092 twins aged 8-11 (Wardle, Carnell, Haworth, & Plomin, 2008).
In it, children born since the genesis of the pediatric obesity epidemic were found to have an affected BMI and rate of abdominal adiposity due to high genetic contributors.
So there is a consensus in the research that genetic factors contribute to obesity.
Further, the idea of genetics being causative of obesity was observed in a milestone study in 1986, when Stunkard et al. showed that 540 adopted Danish twins body fat percentage was nearer to their biological parents than their adopted parents they were raised by.
Tyrrell et al. (2017) suggest that socio-economic position may accentuate genetic susceptibility to obesity.
This may mean that the contribution of genetics towards the obesity pandemic may be exacerbated or mitigated based on the interaction of social and economic factors of an individual.
Additionally, a mother’s personal choices, such as nutrition or lifestyle choices around the nativity, could change the developmental programming of her children (Campión , Milagro, & Martínez, 2009).
In comparison, Lillycrop and Burdge (2011) found that maternal malnutrition induces a modification in epigenetic regulation within genes.
This may suggest that genes that influence obesity are not simply inherited but can be modified by maternal nutrition and lifestyle choices. So, genetic factors can induce obesity and, in addition to being inherited solely from the parent, may be altered by lifestyle choices or the environment of the parents while in the womb or during lactation periods.
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Physical inactivity
Finally, physical inactivity can be an additional element of why people are obese.
In modern times, physical inactivity and the ready availability of calorically dense foods have helped create relatively sedentary behaviour in individuals, which, says the World Health Organization, now serves as one of the prime risk factors for obesity (Van der Klaauw & Farooqi, 2015).
Despite this, Leatherdale and Wong (2008) proclaim that physical inactivity and sedentary behaviour should be regarded as distinct from one another, or this would undermine the intricacy of sedentary behaviour.
This is relevant as prevention strategies to combat obesity by enhancing physical activity in a population may not be feasible if the sedentary behaviour rate remains high and vice versa as they correlate with one another.
The contribution of physical inactivity towards obesity can be observed in a 2004 study by WC Roberts concerning the Amish community.
In it, Roberts found that Amish men and women were found to have a daily consumption of macronutrients identical to the average American household.
However, the Amish men and women were also found to have significantly high daily physical activity levels and an obesity rate between 0% and 9%. Still, a fraction compared to the American obesity rate.
This is compared to a systematic review by Fogelholm and Kukkonen- Harjula (2000), which denoted that individuals who did not participate in physical activity underwent more weight regain than those who did.
These findings reaffirm the notion that physical inactivity may be a contributing element to obesity.
In addition to this, a study by King et al. (2001) showed that individuals who engaged in a minimum of 5 sessions of physical activity per week had a 50 per cent less chance of obesity risk than physically inactive people.
Ironically, because of the effects of genetic elements on physical activity, it is conceivable that those who do not participate in exercise is because they are genetically programmed to do so (Pietiläinen et al., 2012).
In consequence, physical inactivity can account for obesity.
However, it’s important to note that it may be a multifactorial dilemma incorporating genetic factors and sedentary behaviour rather than a sole contributor.
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Conclusion
In conclusion, depression can be a reason why people are obese in addition to a consequence of it.
Inflammation has also been suggested as a key mediator between the connection of depression and obesity.
Another reason why people are obese could be the result of abnormal brain interactions brought on by chronic stress. Moreover, it was found that the built environment is a cause of obesity.
Still, a lack of a built environment in rural settings can be a factor contributing to obesity also.
Furthermore, genetic factors may be a reason why people are obese as they may be modified in the womb or in the early stages of the lactation period.
Finally, physical inactivity is a cause of obesity, but its strong correlation with sedentary behaviour should be considered.
References
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