Stress may counteract the beneficial effects of a healthful diet, a study in Molecular Psychiatry suggests.

The study, a double-blinded randomized trial, looked at 58 women who first ate a meal high in saturated fats, the kind found in meat and butter. Then, one to two weeks later, the women ate a meal low in saturated fats. The only difference between the meals was in the ratio of saturated fats to unsaturated. In all other respects — number of calories, types of food, and amounts of fat, carbohydrate and protein — they were identical.

Before each meal, the women completed several well-validated questionnaires assessing symptoms of depression over the past week and the number of daily stressors in the past 24 hours. Researchers took blood samples before and after each meal.

Among women who had low levels of stress, markers of inflammation tended to be higher after eating the meal containing high levels of saturated fat than after the low saturated fat meal.