Stress and depression have long been linked with a heightened risk of weight gain, but a new study sheds light on how those mental states may alter the way the body processes fatty foods.
Compared to women without stress in the study, stressed-out women burned both calories and fat more slowly for seven hours after eating the equivalent of an average fast-food burger meal.
“Stress can promote weight gain by slowing your metabolism,” Janice Kiecolt-Glaser told Reuters Health.
“The difference with one stressor versus none the day before was 104 calories, which is no big deal on a daily basis, but over the course of the year that would be up to 11 pounds,” said Kiecolt-Glaser, a researcher with The Ohio State University College of Medicine, who led the new study.
For their experiment, published in Biological Psychology, Kiecolt-Glaser and her colleagues enrolled 58 middle-aged women to eat high-fat meals on two separate days while their metabolism was monitored.
To prepare for the study, the women were provided with three standardized meals a day to eat at home on the days leading up to their admission to Ohio State’s Wexner Medical Center.
Then on each day of the study, the participants answered questionnaires designed to assess their depression symptoms and their usual diet and physical activity. They were also asked about any stressful events that occurred on recent days.
Researchers began by measuring how many calories each woman burned while at rest. Next, the women were given a test meal consisting of eggs, turkey sausage, biscuits and gravy.
The meals contained about 930 calories and 60 grams of fat, around the same amounts of fat and calories as a double cheeseburger and fries from the leading fast food restaurant chains, according to the researchers.
On one of the days, the women were given a version of the test meal that was high in saturated fats, and then on the other day they were given a meal high in monounsaturated fats from sunflower oil.
Metabolic tests to see how fast fat and calories were being burned were repeated every hour for seven hours after the meal. In addition, the researchers tracked levels of the stress hormone cortisol, insulin, glucose and blood fats.
A total of 31 women reported at least one stressful event from the day before and 21 reported stressful events on both visits. Six of the women had no stressful events.
On average, the women in the study who had experienced stressful events burned 104 fewer calories than the women with no stress during the seven hours after eating either of the high-fat meals.
The researchers also found that women who had been stressed the day before had higher insulin levels and burned fat at slower rates – both conditions that promote fat storage and are associated with weight gain.
A history of depression did not affect the women’s metabolic rate, although women with depression tended to have high levels of cortisol, which is thought to promote storage of particularly unhealthy fat in the upper abdomen.
Women who had depression combined with any stressors also tended to have a steeper rise in blood fats immediately after the meals.
The only difference between results following the meal high in saturated fat versus monounsaturated fat was a steeper rise in blood sugar after the latter, which the researchers found surprising and said requires further study.
The authors acknowledge some limitations to the study – 38 of the participants were breast cancer survivors, which could have affected the results, although they note that the responses did not differ between those women and the ones who had not had cancer.
The results don’t reveal how the body might respond to low-fat or balanced meals, they add. And it’s also not clear if the findings would apply to men, although Kiecolt-Glaser thinks the effect would be similar.
“It’s hard to tell for sure because they have higher lean body mass, which is one of the factors that goes into resting energy expenditure, but otherwise I don’t see a reason why it wouldn’t,” Kiecolt-Glaser said.
Brian Baldo, a researcher in the department of psychiatry at the University of Wisconsin who was not involved in the study, said one theory about stress and obesity is that eating comfort foods high in fat and calories is a way of self-medicating to calm an overactive stress response.
“This study shows another mechanism toward obesity,” he told Reuters Health, adding that the new findings show recent stressors could affect the physical processes that lead to obesity, including lower resting energy expenditure and less burning of fat.
In effect, Baldo said, “The stress directs you to eat higher fat food, and it also prevents your body from trying to effectively burn that fat off and instead you end up storing it,” he said. “So it’s a double whammy.”