New study reveals connection between body fat and depression

A large-scale study has found that adults with higher percentages of body fat, especially in the legs, gynoid region, and head, tend to report more symptoms of depression. This connection was most evident among men and those classified as underweight or overweight. The findings, published in the Journal of Affective Disorders, suggest that the distribution of body fat—not just overall body weight—may play a meaningful role in mental health.

While obesity and depression are known to often co-occur, many past studies have relied on body mass index (BMI) to define obesity. But BMI doesn’t distinguish between fat and muscle, nor does it capture where fat is located in the body. This limitation has led to mixed results in previous research. The current study aimed to take a closer look by using more precise tools to measure fat percentage in specific areas of the body.

The researchers used data from 10,694 adults who took part in the National Health and Nutrition Examination Survey (NHANES), a nationally representative study conducted in the United States. These participants had completed full-body scans using dual-energy X-ray absorptiometry (DXA), a technology that accurately measures fat, muscle, and bone. The scans allowed the researchers to analyze fat percentage in eight distinct regions: the legs, arms, trunk, head, android (abdominal), gynoid (hips and thighs), subtotal (excluding the head), and total body.

To assess depression, the study used the Patient Health Questionnaire-9 (PHQ-9), a validated self-report measure of depressive symptoms. A score of 10 or higher on the PHQ-9 was used as a cutoff for clinically significant depression. Researchers also collected information about participants’ lifestyle habits, socioeconomic status, medical conditions, and biological markers, which allowed them to adjust their statistical models for many possible confounding factors.

The results showed that people in the highest quartile for total body fat had a significantly higher likelihood of reporting depression compared to those in the lowest quartile. This association remained even after adjusting for a wide range of demographic, behavioral, and health-related variables. Notably, the strongest associations were found for fat located in the legs, gynoid area, and subtotal region. People with higher head fat percentage also showed a modest increase in depression risk.

When the researchers examined differences by sex, they found that the association between body fat and depression was stronger in men than in women. This was especially true for fat in the legs and total body fat. In contrast, the connection was weaker or absent in women, except for some regions. This suggests that the effects of fat distribution on mood may operate differently depending on biological sex.

The researchers also looked at whether the association varied across different BMI categories. Among individuals who were underweight or overweight, higher body fat percentages in several regions were consistently linked with increased depression risk. Interestingly, this pattern was not as clear in participants with a BMI in the normal range. This finding challenges the assumption that normal-weight individuals are at low risk for depression related to fat accumulation and highlights the importance of examining fat distribution rather than relying on weight alone.

The researchers suggest several possible explanations for these patterns. Biologically, excess fat tissue produces inflammatory molecules that may interfere with brain function and mood regulation. Hormones like leptin, which help control hunger and metabolism, can also become dysregulated in people with higher fat percentages, possibly affecting brain systems involved in emotion. Psychosocial factors may also play a role. Individuals with higher body fat, especially in visible areas, might experience greater stigma or body dissatisfaction, both of which can contribute to depression.

This study adds to a growing body of evidence that body composition—and where fat is stored—can affect mental well-being. While BMI has long been the go-to measure in public health and clinical settings, this study shows that it may be too blunt an instrument to capture the nuances of how body fat influences mental health.

Despite its strengths, the study has some limitations. Because it was cross-sectional, it cannot determine whether higher body fat leads to depression or whether depression contributes to changes in body composition. Depression itself can influence eating habits, physical activity, and metabolic processes, which could alter body fat levels over time. The study also relied on a single self-report questionnaire to assess depression, without clinical interviews or additional mental health screenings. Moreover, since the research focused on a United States population, the findings may not apply to other cultural or healthcare settings.

Future research could address these limitations by following participants over time to explore how changes in fat distribution might influence mental health. It would also be useful to examine how interventions that reduce specific types of body fat—through diet, exercise, or other means—might affect depression symptoms, especially in men or in people whose weight falls outside the typical range.

The study, “Association between body fat percentage and depression: A cross-sectional study of NHANES,” was authored by Wenjun Gu, Kunming Bao, Xiaoming Li, Shaohang Xiang, Junhao He, Jinning He, Lixin Ye, and Zhidong Huang.