According to a study published in the Journal of Clinical Endocrinology & Metabolism, sugar-sweetened beverages can suppress the hormone cortisol and stress responses in the brain.
Beverages sweetened with aspartame, however, do not have the same effect."This is the first evidence that high sugar—but not aspartame—consumption may relieve stress in humans," says Kevin D. Laugero of the University of California, Davis, and the U.S. Dept. of Agriculture's Agricultural Research Service, one of the study's authors. "The concern is psychological or emotional stress could trigger the habitual overconsumption of sugar and amplify sugar's detrimental health effects, including obesity."
In the parallel-arm, double-masked study, researchers assigned eight women aged 18–40 to consume one aspartame-sweetened beverage and 11 others to drink one sugar-sweetened beverage at each meal over a 12-day period. They found a diminished cortisol response during a math test in the women who drank the sugar-sweetened beverages. This group also showed more activity in the hippocampus than the women who drank aspartame-sweetened beverages. The hippocampus, a part of the brain involved in memory and sensitive to stress, typically is less active when the body is under stress.
According to Laugero, these findings help explain how sugar positively reinforces people's temptation to eat comfort food when they are stressed. "The results suggest differences in dietary habits may explain why some people underreact to stressful situations and others overreact," he says. "Although it may be tempting to suppress feelings of stress, a normal reaction to stress is important to good health. Research has linked over- and under-reactivity in neural and endocrine stress systems to poor mental and physical health."