Losing weight tends to be more difficult for people who are depressed. But if successful, many find that as the number on the scale decreases, their happiness increases. Findings such as these from long-term observational studies highlight the connection between depression and obesity, two extremely prevalent conditions with profound effects on health and quality of life.

In an effort to confirm the obesity-depression link and to determine how other mental disorders are related to weight, researchers analyzed health data collected via interviews of more than nine thousand Americans. Their study, in the July 2006 Archives of General Psychiatry , reports that obesity is associated with a 25% increase in the odds of having a mood disorder (such as anxiety or depression) and a 25% decrease in the odds of having a substance use disorder.

About the Study

Researchers from the Center for Health Studies in Seattle analyzed data from the National Comorbidity Survey Replication (NCS-R). The NCS-R consists of health interviews of 9,125 Americans, from 48 states and varying backgrounds, conducted from 2001-2003. The interviews collected details about health status and assessed potential mental disorders such as depression, anxiety, and substance use. Volunteers reported their heights and weights, from which body mass index (BMI) was calculated; BMI greater than 30 was classified as obese. Researchers analyzed the data looking for associations between BMI and mental disorders.

Compared with study volunteers who were not obese, obese people were about 25% more likely to have depression or an anxiety disorder. The obese volunteers were also about 25% less likely to have a substance use disorder. The link between obesity and mental disorders was strongest among non-Hispanic whites and college graduates. These findings remained significant after controlling for the effects of age, gender, smoking, and other psychiatric disorders.

A potential limitation to this study is that height and weight were reported by the volunteers, rather than measured by the researchers. People tend to underestimate their weights when self-reporting.

How Does This Affect You?

This study agrees with previous research findings—depression and anxiety are linked with obesity. Which comes first, the mental distress or the weight gain, likely depends on personal factors, as there are plausible explanations in both directions. For example, this study’s strongest associations were seen among college graduates and non-Hispanic whites—groups in which obesity is less common, more stigmatized, and therefore, more likely to lead to depression and/or anxiety. On the other hand, symptoms of depression may include overeating and lack of physical activity, both of which lead to weight gain. There may also be a third, unidentified factor that predisposes to both weight gain and mental disorders.

Regardless of which came first, the key is to recognize that if you are struggling with weight and a mental disorder, these conditions are likely related with one potentially feeding the other. If this is the case, it makes sense to seek a treatment approach that tackles both simulataneously, such as a weight loss program that incorporates psychological counseling. Exercise, in particular, would be an essential component of this program, since it has been shown to effectively treat both conditions.