Studies have shown a strong correlation between common mental disorder and obesity. It is suggested that people with repeated episodes of common mental disorder are particularly at risk of subsequent obesity.
There are several possible reasons or explanations for the finding that persistent common mental and emotional problems like anxiety, depression, stress, fear are the risk factors for obesity.
In a prospective cohort study with four measures of common mental disorders and obesity over 19 years conducted at the civil service department in London it was concluded that in the British adults common mental disorders lead to an increased risk of obesity. The association was found to be cumulative such that the people with chronic or repeat episodes of common mental disorder are particularly at the risk of weight gain. The reasons stated in the study for this association are as follows:
Common mental disorders are known to be associated with eating disorders (disordered eating), both over-consumption and under-consumption, which are responsible for increase in body weight and fat.
The stigma, shame, lack of confidence attached to obesity may lead to increased risk of anxiety and depression.
Excessive emotional eating (nervousness, celebration, depression, lonliness etc) for a long period of time can cause sudden weight gain.
Physical inactivity, a major contributing factor to obesity, is found to be more prevalent among people with mental health problems. The study states that some randomized controlled trials suggest that exercise could reduce depressive symptoms among people with a diagnosis of depression.
Commonly used drug treatments for mental disorders have known side effects that may result in weight gain (tricyclic antidepressants), weight loss (selective serotonin reuptake inhibitors), or both (short term and long term effects of selective serotonin reuptake inhibitors).
Biological factors, such as dysregulation of the hypothalamic-pituitary-adrenocortical axis, may strengthen the link between mental disorders and obesity. For example, some evidence exists of abnormal concentrations of hormones of the hypothalamic-pituitary-adrenocortical axis among obese people with coexisting depressive symptoms. All these mechanisms are likely to increase the risk of obesity in a dose-response fashion. These findings suggest that people with chronic or repeated episodes of common mental disorders are at high risk of obesity. Reference:
Kivimaki M et al. "Common mental disorder and obesity: insight from four repeat measures over 19 years: prospective Whitehall II cohort study". BMJ. 2009; 339:b3765