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Exercise is often recommended to obese individuals who want to lose weight as it has shown to be an effective way to burn calories and improve metabolic health. While the physical benefits are well understood, researchers in a new study, wanted to further explore the role of the brain-gut microbiome (BGM) system in mediating the psychological beneficial benefits of exercise in individuals with a high body mass index (BMI). This exciting new research suggests that physical activity has the ability to alter the bacteria in the gut microbiome, leading to better mental health outcomes.

“Obesity has doubled in the adult population…[and] the number of obese children has quadrupled [in the past few decades]…”

Obesity has doubled in the adult population over the past few decades, with an estimated 650 million adults now obese. It has become a global epidemic, and having a high BMI poses a serious threat to both an individual’s life span and their quality of life. High BMIs and often associated metabolic syndrome, and increase the risk for many of the disorders making up the current chronic disease epidemic.

Furthermore, the number of obese children has quadrupled. The prevalent rate of obesity is highly alarming, making it an issue that is in need of immediate attention and interventions. Obesity, meaning a BMI greater or equal to 30, is a chronic complex disease that can lead to other medical complications, impairing both physical and mental health.

Having a high BMI is linked to non-communicable diseases that decrease healthspan and often decrease lifespan such as diabetes, infertility, poor bone health, hypertension, cardiovascular disease, and cancer. While the negative effect that obesity has on physical health is often well understood, it can also have a significant impact on mental health too.

“It has become a global epidemic, and having a high BMI poses a serious threat to both an individual’s life span and their quality of life.”

As expected from a complex system, the relationship between BMI and mental health disorders is a two-way street, which explains how obesity is often comorbid with psychiatric disorders. Individuals who are struggling with mental health disorders may gain excess weight as a side effect of their mental condition. On the other hand, obese individuals may develop poor mental health as a result of weight-related discrimination.

Additionally, obese individuals who have experienced weight-related discrimination often end up gaining more weight overtime since they will turn to maladaptive behaviors in order to cope with their problems. Some of these habits include binge eating, emotional eating, and food addiction which all lead to an overall increase in calorie consumption, likely resulting in a rising BMI overtime.

“Obese individuals who have experienced weight-related discrimination often end up gaining more weight overtime since they will turn to maladaptive behaviors in order to cope with their problems.”

Individuals who are faced with high stress situations, such as being discriminated for their weight, not only overeat often, but are also likely to turn to high-risk behaviors, such as drug use. They may struggle with handling stressful situations and therefore likely lack resilience. Resilience is the ability to cope with stressful situations in a positive, adaptable way. Our level of resiliency can depend on our genetics, environment, and close relationships.

Arpana Church PhD, Co-Director of the Goodman-Luskin Microbiome Center at the University of California Los Angeles (UCLA) and co investigators aimed to explore possible interventions that target the brain-gut microbiome system for managing a stress-related disorder such as obesity. The investigators set out to determine if exercise has the potential to improve the psychological state of individuals, and if this benefit is mediated by the BGM system. Specifically, the study was designed to understand whether physical activity could alter the bacteria in the gut microbiome in individuals with a high BMI, and lead to better mental health outcomes.

Their results confirmed their hypothesis that physical activity is associated with significant alterations in the BGM system, that are associated with better psychosocial measures in populations with high BMIs. At the same time, they found that low physical activity levels were more likely to be associated with greater degree of food addiction, whereas high physical activity participants had the lowest food addiction scores.

These psychological findings were associated with altered connectivity within a specific brain network, the so-called default mode network. This network is a system of connected brain areas that show increased activity when a person is not focused on what is happening around them. Alterations have been reported in several brain disorders including chronic depression. In addition, the investigators found a significant association between higher levels of physical activity and greater resilience.

Resilience plays an important role when it comes to one’s emotional well-being and is a known protective factor against the development of psychiatric disorders such as depression and post-traumatic stress disorder (PTSD).

Furthermore, greater emotional resilience has been shown to be protective against developing obesity, regardless of other factors, such as level of income, that may increase risk of obesity. The way an individual copes and responds when faced with stress has a significant effect on both their mental and physical health. With higher levels of resilience, individuals will often be less inclined to binge eat and more motivated to make healthy dietary choices. The association between higher levels of physical activity and greater resilience highlights the importance of exercise on overall health.

“…greater emotional resilience has been shown to be protective against developing obesity, regardless of other factors, such as level of income, that may increase risk of obesity.”

The researchers also found that the prevalence of a group of beneficial gut bacteria called Prevotella, was noticeably increased in individuals who had moderate to high levels of physical activity. Prevotella is associated with improvements in metabolic health, digestion, and well-being.

Previous studies have shown that individuals with mental health disorders such as depression or anxiety have lower levels of Prevotella. These findings suggest that exercise could promote good gut bacteria that is protective against mental health disorders.

Even though the findings are intriguing, the study only demonstrated correlations between measures of obesity, psychological variables, physical exercise and the BGM system. A prospective clinical trial design would be required to determine a causative relationship between these variables.

However, one may speculate that targeting obesity and the observed alterations in the gut microbiome with physical exercise, diet and behavioral interventions to increase resilience have the ability to lead to better mental health outcomes and reduction of obesity.

Healthy plant-based diets, like the Mediterranean diet and specifically the higher fiber intake and less intake of high-glycemic index sugars have previously been shown to be associated with a greater prevalence of Prevotella populations.