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.