When we gain body fat, some individuals may notice changes to their thinking. But why? It seems that inflammation may be the culprit.
A new study tested the association between thinking speed and how body weight and depression are involved. On average, the brain’s processing speeds slows as body weight increases or depression symptoms worsen.
As body fat percentage rises, inflammation in the body also increases. We can measure this level of inflammation using specific biomarkers in the blood and brain. (For example, common biomarkers include: tumor necrosis factor-α, interleukin-8, and macrophage inflammatory protein-1β.) These are also higher based on the severity of depression symptoms.
The insidious thing about inflammation is that it takes energy. And as a result, it can cause us to feel more fatigued.
One reason for lower daily energy in inflamed individuals is due to loss of muscle. Studies confirm that muscle declines faster in those with inflammation because individuals don’t feel energized enough for sufficient physical activity. This can create a vicious cycle. Not enough movement leads to progressive muscle loss, further reducing daily energy and physical capacity.
In individuals who are at a healthy weight for their height, depression can slow brain processing speed. And in individuals who are obese but not depressed, percentage body fat associates with feelings of fatigue. Research confirms that body fat percentage “independently explains a significant amount… of general and physical fatigue.”
High bodily inflammation is a common link, but can we limit fatigue by reducing inflammation? The answer appears to be YES. For instance, blocking some of those inflammatory markers “partly improves motor fatigue”. We can’t experimentally block inflammation in the body forever, but at least this helps to clarify that inflammation can sap daily energy.
Inflammation is common for both obesity and depression, and one condition may set you up for the other. A meta-analysis of data from almost sixty-thousand study participants suggests that high body fat percentages can increase depression risk and vice versa.
Specific findings suggest that:
Although the meta-analysis looked at adults over 20, similar results are observed in studies that examined specific age ranges. For instance, in adults 27-47 years of age, percentage body fat is “associated with poorer performance on measures of executive function.” (Executive functions involve our ability to complete tasks and remain focused on goals.) And much like the bidirectional relationship shown in the meta-analysis, this research showed that the presence of depressive symptoms early in the study was a risk factor for weight gain a year later!
A study on young adults (18-21 years of age) had similar results. In young adults, obesity is associated with slower thinking speeds. Importantly, study participants were capable of the same level of performance. This means their cognitive processing was slightly slower on average, even though they could get to the right answers at the same rate as their healthy-weight peers. (It is like they can achieve the same test grade, but may take a little longer to complete the exam, for example).
Inflammation matters, and even though it tends to increase with age, recent research suggests that inflammation-based changes are also evident in childhood.
Studies indicate that children who are at a healthier weight (for their height) score better than overweight and obese children in working memory tests. (Interestingly, this holds true except for the domain of remembering food and drink-related items such as the logos for fast food and sugar-sweetened beverages.) This may be part of the reason we see lower academic achievement based on body fat percentage according to at least nine other studies in children all over the world. And it may help explain why in long-term studies, body fat percentage at age ten has been a strong predictor of academic performance in high school, even controlling for TV watching and socioeconomic status.
Before you start making adjustments, a friendly reminder to involve your doctor. One reason is because fatigue, depression, and weight gain may reflect a specific medical condition. For example, did you know that with low thyroid hormone, many feel the symptoms of depression and gain body fat? This can be treated with a single daily tablet if symptoms are shared with medical care providers.
Another reason to involve your doctor is because obesity can change how our bodies metabolize drugs, so they may need closer collaboration with health care teams to manage certain conditions. This includes depression. For example, obese men with depression had limited therapeutic benefit in response to certain antidepressants. Other antidepressant benefits are similarly reduced in overweight individuals and may be less effective in obese individuals.
It is helpful to note that the references about depression and obesity and inflammation are all based on averages. It is possible to be at a healthy BMI and have high inflammation, or to be carrying a lot of excess body fat and have low inflammation. A big part of what determines inflammation is your daily habits.
As we adopt healthier lifestyle habits, inflammation subsides. This includes things like less sugar and more vegetables and fruits. And more movement can also help. Treo members gain access to habit-building resources that help them make the adjustments they desire. By empowering anti-inflammatory lifestyles, we can help others feel better day by day, so they can lead healthier, energized lives. Interested in learning more? Reach out to us at info@treowellness.com.
As Treo’s Global Wellness Researcher, Karlie uses recent research findings to support healthier daily habits. Karlie earned her doctorate in Neuroscience and Behavior and bachelors in Health and Exercise Science.
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