An increased risk of obesity long linked to stress or depression could be because such mental states change the way body processes fat, a study suggests.

In a study at Ohio State University, women who reported they were stressed were found to burn fat and calories at a slower rate for as much as seven hours following consumption a high fat meal than did women without stress.

Women participants were given a meal containing 930 calories with 60 grams of fat, after which their metabolic rates were assessed and measurements taken of trigycerides, blood sugar and insulin, and cortisol, a stress-related hormone, the researchers reported in the journal Biological Psychiatry.

Before the meal, the participants were asked about any depression symptoms and any stressful events that occurred on recent days. The most commonly reported events were interpersonal issues, such as problems with children, arguments with spouses or work-related pressures.

Such stresses were found to have an impact on the women's metabolism, the researchers said.

"Stress can promote weight gain by slowing your metabolism," study leader Janice Kiecolt-Glaser of the OSU School of Medicine said.

"The difference with one stressor versus none the day before was 104 calories (burned), which is no big deal on a daily basis, but over the course of the year that would be up to 11 pounds," she said.

Women who reported stress the day prior to consuming the high-fat meal also had elevated levels of insulin levels and a lower rate of fat burning, both of which promote the storage of fat and are linked with weight gain, the researchers said.

While there is no evidence a history of depression affects metabolic rate, they said, women suffering from depression tended to exhibit increased levels of the hormone cortisol, thought linked to storage of unhealthy fat around the region of the upper abdomen.

The overall findings strongly suggest that over an extended period of time, stress can lead to weight gain, Keicolt-Glaser said.

"We know from other data that we're more likely to eat the wrong foods when we're stressed, and our data say that when we eat the wrong foods, weight gain becomes more likely because we are burning fewer calories," she said.

That become a factor with a diet heavy in fatty foods, stud co-author Marhta Belury said.

"We know we can't always avoid stressors in our life, but one thing we can do to prepare for that is to have healthy food choices in our refrigerators and cabinets so that when those stressors come up, we can reach for something healthy rather than going to a very convenient but high-fat choice," she said.