Accumulating fat around the belly has long been linked to metabolic syndrome, a collection of problems that include high blood pressure, cholesterol and blood glucose.
Recently, metabolic syndrome was linked to a greater risk of Alzheimer's disease and other forms of dementia later in life.
Now depression has been added to the list of ailments linked to excessive belly fat, and losing weight through dieting doesn't seem to reverse the problem.
"Weight gain is the major contributor to metabolic syndrome and depression, but we also observed that in many people who are obese, losing weight is not enough to reduce the symptoms of depression," said An Pan, a nutritionist at the Harvard School of Public Health and one of the authors of the study, which appears in a recent issue of Diabetes Care.
"In fact, losing weight by dieting may actually increase stress and depressive symptoms," Pan says.
A better approach, he says, would involve more exercise, which helps the body burn some of the deep fat packed around abdominal organs - the cause of the large belly often carried by people with metabolic syndrome.
Those wanting to lose weight are encouraged to eat a healthy diet and participate in physical activity. Pan also recommends psychiatric counselling for people who are depressed.
The paper found evidence of a vicious cycle - metabolic syndrome contributes to depression, and depression contributes to metabolic syndrome, apparently by causing people to overeat.
Pan and the other authors of the paper suggest several possible mechanisms for this two-way interaction.
For example, depression affects the metabolism in ways that could increase blood pressure, reduce the body's ability to absorb glucose and promote the accumulation of belly fat. Also depressed people are more likely to lack the motivation to get exercise.
On top of that, some antidepressant medications promote weight gain.
In the other direction, metabolic syndrome promotes inflammation, which has been linked to depression, and makes the body less sensitive to leptin, the hormone that suppresses appetite after eating.
Low levels of leptin, as well as leptin insensitivity, have been shown to produce depressive symptoms. Also, damage to blood vessels in the brain caused by high blood pressure and other consequences of metabolic syndrome may produce symptoms of depression, and are believed to promote dementia, as other studies have found.
Another study, just published in the journal Neuropsychopharmacology, reports that pioglitazone, a drug that helps prevent diabetes by enhancing the body's sensitivity to insulin, also appears to boost the effectiveness of antidepressants in people with major depression.
The drug helped even when taken by depressed people who didn't have the metabolic problems that signal the approach of diabetes. The authors believe that pioglitazone (sold as Actos) counteracts depression by helping the body use glucose more efficiently, just as exercise does.
Apparently the accumulation of belly fat, which may be a consequence of too much sugar in the blood, also contributes to elevated blood sugar and several other problems, including depression.
"I think the major message of our paper is that depression, cardiovascular disease, stroke and other problems begin early even in people who do not have diabetes," says Pan.
"So prevention should begin early for people with metabolic syndrome. We should pay attention to their mental health, and for people with mental health problems we should monitor their blood glucose, blood lipids and blood pressure to control their risk of cardiovascular disease and stroke."
- Scottish News and Sport