Eating a fatty meal after a stressful day can slow a woman's metabolism and make her gain weight.
Women who experienced one or more stressful events burned significantly fewer calories than those who did not, scientists found.
The difference was big enough to pile on almost 5kg over the course of a year, prompting a warning not to resort to unhealthy comfort food at times of stress.
Stressed women had higher levels of insulin, which contributes to fat storage. Their fat was also less likely to be oxidised - converted into a form that can be used as fuel.
US lead scientist Professor Jan Kiecolt-Glaser, from Ohio State University, said: "This means that, over time, stressors could lead to weight gain.
"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."
The scientists questioned 58 middle-aged women about how stressed they were the previous day before giving them a meal containing 930 calories and 60 grams of fat.
On average, those women who reported experiencing one or more stressful events burned 104 fewer calories than non-stressed women in the seven hours following the meal.
Over the course of a year, slowing metabolism by this much could result in weight gain of almost 5kg, said the researchers whose findings appear in the journal Biological Psychiatry.
Stressful events reported by the women included arguments with work colleagues or spouses, disagreements with friends, trouble with children or job-related pressures. Only six women claimed to be completely stress-free.
The research meal comprised eggs, turkey sausage, biscuits and gravy - roughly the calorie and fat equivalent of a double-layer hamburger and French fries.
A history of depression alone did not affect metabolic rate. But depression combined with stressful events led to a steeper rise in triglyceride blood fats - a risk factor for heart disease - after the meal.
"The double whammy of past depression as well as daily stressors was a really bad combination," said Prof Kiecolt-Glaser.
The scientists are not sure men would experience the same pattern, since they tend to have more muscle which affects their metabolic rate.