Obesity is the accumulation of body fat to the extent it harms one’s health. Defined as a body mass index (BMI) ≥30 kg/m2, more than 650 million people (13%) worldwide have obesity. In Canada it’s even higher at 27%, while in the United States, it’s 42%. We often think of obesity as it relates to physical health. And indeed, people with obesity are more likely to get type 2 diabetes, heart disease and cancer. Yet obesity can also affects one’s mental well-being.

social stigma and obesity

The Effect of Obesity on Mental Health

People with obesity commonly face stigmatization and body shaming throughout their lives. It can start in early childhood and continue into later life and consist of being viewed as lazy, less likely to get married and get paid less at jobs. This can lead to lower self-confidence, insecurity and loneliness. As a result, obesity increases one’s chances of having depression and anxiety disorders. In addition, suicidal thoughts tend to be greater in people with obesity who’ve faced discrimination.

How we think is also impacted. Cognitive function, which includes mental abilities such as learning, memory and problem solving, is also affected. People with obesity tend to have lower cognitive function compared to people without obesity. And having obesity during middle-age may increase one’s chances of getting dementia.

Fat around the waist may be of even more of a concern. A higher waist circumference was associated with greater chances for cognitive decline and dementia in people aged 60 to 101. In contrast, a higher BMI was associated with lower chances. This may be due to a lower BMI in later life being associated with underlying disease due to lower muscle mass. When both body fat and fat around the waist were measured directly by MRI, high levels were both associated with lower cognitive function.

scientist linking obesity and mental health

Linking Excess Body Fat with Mental Health

It’s not entirely clear how excess body fat is linked to poor cognition. People with obesity tend to be less active, experience more stress and have poor nutrition. These lifestyle behaviours are associated with poor cognitive function and greater chances of getting dementia. In addition, risk factors for heart disease, such as type 2 diabetes, high blood pressure and high cholesterol, are more common in people with obesity. Again these risk factors are associated with poor cognition.

However, additional factors are likely involved. Excess fat can lead to a greater production of inflammatory factors. This leads to chronic inflammation, which can increase the chances of getting depression and dementia. There is also evidence obesity may impair brain function related to memory and ability to learn new things.

balancing obesity and mental health

Can weight loss improve mental health?

If excess body fat is related to mental illness and poor cognitive function, can weight loss (or rather fat loss) improve mental health? In people with optimal BMI, weight loss may be associated with worse cognitive function. Indeed, being underweight is believed to increase chances of poor cognitive function. Similarly, studies in older adults suggest weight loss may be associated worse cognitive function.

However, people with obesity undergoing intentional weight loss do see improvements in cognitive function. Many of these studies used dietary interventions for weight loss, which itself can improve cognition. However, weight loss through bariatric surgery has resulted in improvements in memory three years later. This suggests losing fat has the potential to improve cognitive function. Additional studies have indicated weight loss may also improve mood.

While weight loss isn’t easy, understanding the links between excess body fat and mental well-being can help in developing prevention and treatment strategies for dementia in later life.

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