Experts have told us for many years that chronic stress leads to expanding waistlines. While this may be true for a variety of reasons (ranging from biological to psychological), a new study suggests that the effects of stress on the waistline may actually be more modest than previously thought.

Researchers conducted a meta-analysis of 32 earlier studies that tracked stress and weight gain over a number of years. The studies looked at various kinds of stress, including work-related stress, acute and chronic life stresses. Changes in weight were measured by several means including body mass index (BMI) and waist circumference.

Though women are thought to be more sensitive to stress in general, men tend to have a more pronounced response to acute stress (their heart rates and cortisol responses are greater than women’s).

When all was said and done, stress was found to play a significant role in weight gain in only a minority of the studies. In fact, 69% of the studies found no link at all between stress and weight, and only 25% of the studies found that more stress was connected to weight gain throughout the years. Interestingly, 6% found that more stress was linked to less weight gain.

When the researchers looked at work stress and general life stress separately, they found no significant associations. They do say that acute stress and the stress of major life events tended to have a greater effect on men’s weight than it did on women’s. Though women are thought to be more sensitive to stress in general, men tend to have a more pronounced response to acute stress (i.e., their heart rates and cortisol responses are greater than women’s).

Why is there such a fuzzy relationship between stress and weight? Part of it may be the fact that people react to stress so differently; some may "stress eat" while others lose their appetites when they are stressed out. Stress-related weight gain may also have to do with the kinds of foods we choose when we are stressed (e.g., ice cream seems to solve problems better than salad), and the fact that exercise often loses its appeal during times of stress. Of course, when the stress hormone cortisol is chronically elevated, the body naturally holds onto weight, though this effect may be more modest than we like to think. In any case, stress can wreak havoc on the body in a number of ways, some more significant than others, so it is important to find effective ways to release it.

The study was carried out at University College London and published in the October 14, 2010 online issue of Obesity.