Obesity and depression, are two diseases that feed on each other. Globally, approximately 280 million people suffer from depression. It is one of the leading causes of disability worldwide. At the same time, the number of cases of obesity has almost tripled since 1975. However, obesity entails a high risk of other chronic diseases (diabetes, heart disease, musculoskeletal disorders, etc.). In addition, it is now proven that it is frequently associated with depression. “Obese people experience stigma and this inevitably affects their mental health,” says Elina Hyppönen, director of the Australian Center for Precision Health at the University of South Australia. In reality, the two conditions feed each other via a terrible vicious circle.
When depression “feeds” obesity and vice versa
Obesity essentially results from an energy imbalance between calories consumed and calories expended. Processed products, very fatty and very sweet, are numerous and widely consumed. In addition, many people do not get enough physical exercise. However, we know that adipose tissue harbors immune cells, which produce pro-inflammatory proteins. Consequently, obese people tend to produce these molecules in excess. Among these proteins: cytokines.
Several studies have shown that cytokines down-regulate serotonin levels. It is a neurotransmitter widely involved in mood and the state of happiness. Specifically, cytokines stimulate an enzyme that alters the supply of amino acids necessary for the production of serotonin. This explains why, from a biological point of view, obese people are more prone to depression.
At the same time, studies have shown that individuals suffering from depression, regardless of their body mass index (BMI), have higher cytokine concentrations than the rest of the population. However, pro-inflammatory cytokines can lead to insulin resistance. Which can lead to type 2 diabetes. This type of diabetes comes with an increased risk of gaining weight. Therefore, cytokines caused by depression can lead to obesity, just as cytokines caused by obesity lead to depression! “It’s a vicious circle,” says Hubertus Himmerich, a psychiatrist at King’s College London.
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Several reciprocal biochemical links related to obesity
And as if that were not enough, another molecule intervenes in this vicious circle. It is cortisol, also called the “stress hormone”. In response to a stressful situation, cortisol raises blood sugar (blood sugar) to supply the brain with glucose. Studies in macaque monkeys and later in humans found that depressed individuals had significantly higher cortisol levels than those with good mental health. Stress and depressive disorder were therefore associated with prolonged cortisol secretion.
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But cortisol doesn’t only regulate blood sugar. This hormone regulates the metabolism of lipids and proteins, inhibits certain responses of the immune system and is also involved in the regulation of the circadian cycle. It also increases appetite, which potentially leads to weight gain. “There is a self-soothing aspect to it. This is why you crave chocolate ice cream, and not carrots, when someone breaks up with you,” says Valerie Taylor, a psychiatry researcher at the University of Calgary.
Let’s summarize. Depression produces high levels of cortisol. It increases appetite and potentially leads to weight gain. But as with cytokines, the effect is unfortunately reciprocal. Indeed, obesity is also correlated with high cortisol concentrations. A meta-analysis on obesity published in 2017 found that for every 2.5 point increase in BMI, there is a 9.8% increase in cortisol in hair.
Conclusion: High cortisol induced by depression may fuel obesity and high cortisol induced by obesity may contribute to intensifying depression.
Therapeutic approaches which need to evolve
People suffering from obesity and depression therefore find themselves in a particularly complex situation. Depression is fundamentally characterized by a loss of motivation. But to fight obesity, you have to eat healthier and exercise. Motivation is essential. Therefore, experts agree that both conditions must now be taken into account in treatments. Indeed, the two are linked. Acting only on one can have unexpected and devastating consequences on the other.
For example, we know that weight gain is one of the side effects of antidepressants. “You take the drug to reduce depression, but it makes you gain weight, which makes your depression worse, so you take more antidepressants, and so on,” Valerie Taylor points out. A study last year also showed that obese people on anti-depressants had an increased risk of complications, particularly diabetes and cardiovascular problems, compared to those who did not take treatment.
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For Richard Morriss, clinical psychiatrist and researcher at the University of Nottingham, obesity should be treated with the same seriousness as anorexia. “Being too thin is considered a mental health issue. But if you’re overweight, it’s still mostly seen as a physical problem,” he notes. In all cases, depression should be treated as a priority. Indeed, as Valerie Taylor points out, it is impossible to make significant changes to your lifestyle until you feel mentally well.
A Better nutrition can help people lose weight and get out of depression. However, studies on the subject are sometimes contradictory. The problem is that people who lose weight too quickly usually gain more of it just as quickly, leaving them in deep distress. However, medical care rarely includes long-term follow-up including the weight stabilization phase. “The combined problem of obesity and depression is unlikely to improve until therapeutic techniques evolve to confront and manage both problems,” Morriss concludes.