To me, it makes perfect sense that depression and obesity go hand in hand because unfortunately, I've experienced both. Depression causes many people to abandon activities that they might enjoy, in part because people who are depressed often lack the energy to participate. Weight gain often comes along with being inactive. Certain medications that are used to combat depression may also cause weight gain. In American society, there's a stigma related to being overweight. Being fat is embarrassing for many people and sometimes other people behave in a hurtful way toward the obese. What's more, being overweight can be physically painful. It can cause stress on the joints and lead to disease. The resulting pain can also cause a person to be depressed.

Dr. Gregory studied more than 9,000 adults and found that depression and other mood disorders were more prevalent in about 25 percent of the obese participants than it was for non-obese participants. The only exception was substance abuse. Obese study participants were about 25 percent less likely to abuse drugs or alcohol than non-obese participants. The study also found that the relationship between obesity and mental illness was the same for men and women.

While I'm not surprised by Dr. Gregory's findings, I do think they are significant. Roughly one-third of American adults are obese, while depression affects about 10 percent of the population. Dr. Gregory hopes his research will remind physicians to be on the lookout for depression in their obese patients and not believe that stereotype that heavy people are always happy.

Dr. Gregory and his colleagues published their research in the July issue of Archives of General Psychiatry.

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About the author: In her spare time, knotheadus writes for Epinions.com and maintains her own Web site, knot-heads.com.