A new study has found that obese men have a much lower risk of suicide, a finding that scientists believe might be related to their higher production of insulin and other hormones that affect mood.
The study, published today in the Archives of Internal Medicine, reported that the men were 42 percent less likely to commit suicide than those at the lower end of the normal weight range.
Lead author Kenneth J. Mukamal of Beth Israel Deaconess Medical Center in Boston said he wasn't recommending that people overeat to stave off depression, saying that obesity carries numerous other health risks, including diabetes and heart disease.
But the results, if replicated in a larger study, point to a new avenue for research into the role of hormones on mood, he said.
"I see this as a springboard for developing new and better ways to prevent suicide because, frankly, we don't have great ones now," Mukamal said.
He cautioned the study was not applicable to women in part because of hormone differences related to gender. In addition, he said, the stigma of obesity falls more heavily on women, causing anxiety and other adverse effects on mood.
"Men can be jolly and fat," he said.
The research was based on the Health Professionals Follow-Up Study, a survey of 45,000 men - dentists, veterinarians, optometrists and others - that began in 1986.
The study examined the relationship between suicide and body mass index, a ratio of weight to height. For example, a 6-foot man who weights 154 pounds has a BMI of 21.
Researchers looked at men with BMIs ranging from below 20, which is considered underweight, to those with a BMI above 30, which is considered obese.
The risk of suicide declined as BMI increased, suggesting that being fat exerted a protective effect against severe depression, the researchers said.
The study found that underweight men with a BMI below 21 had a 39 percent greater risk of suicide than men in the low-normal range of 21 to 22.9.
The analysis was adjusted to take into account chronic diseases such as cancer and diabetes, and antidepressant use.
The researchers surmised that higher amounts of insulin in the obese men increased their levels of serotonin, a key brain chemical that regulates mood. Most antidepressants act on serotonin.
The theory fit with other evidence on the relationship of insulin to mood. For example, the mood of Type 2 diabetics improves after receiving insulin. By contrast, post-partum depression in mothers of newborns is related to a drop in insulin.
Mukamal added that obese men also produce larger amounts of leptin and sex hormones, which might serve to alleviate depression.