Everyday stress can cause metabolic changes that, in the long run, contribute to obesity, according to a recent study by the departments of psychiatry and biomedical engineering at the University of Cincinnati College of Medicine.
Science has long documented that during extreme stress, such as in the experience of war or traumatic grief, victims tend to decrease their food intake, resulting in lower body weight. Recent studies, however, suggest that everyday social stress—tests, public speaking, job and relationship pressures—may have the opposite effect, resulting in overeating and weight gain. With obesity on the rise, scientists have increasingly focused on the causes and effects of weight gain, including the contributions of stress.
Previous studies have proven that number, duration and size of meals have an effect on metabolism. Studies in both animals and humans have shown that eating fewer and larger meals promotes an increase in fat mass and can increase triglycerides, lipids and cholesterol independent of the total calories ingested. On the contrary, weight gain—even while overeating—can be stopped by simply having smaller, more frequent meals. Whether social stress alters the microstructure of food intake, however, was unclear.
In the current study, researchers observed rats exposed to the equivalent of daily stress in humans and analyzed how this stress contributed to the rats’ food intake and meal pattern changes. The study was published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology.
Rats were individually housed for three weeks while scientists observed meal pattern behaviors. The rats were then rearranged to form colonies—four males and two females—and matched with a control group. Within a few days, all colonies formed their own hierarchy resulting in the dominance of one male and the subordination of the other three males.
During this highly stressful event, both subordinate and dominant rats reduced their initial food intake and body weight compared to the earlier habituation period and also compared to the control group.
Once the hierarchy stabilized, however, the dominant rats recovered their food intake relative to the control animals, while the subordinate rats continued to eat less by reducing their number of meals. Furthermore, the subordinate rats ate primarily during lighted periods, showing a change in circadian behavior.
After two weeks, the male rats were individually housed for a three-week recovery period and allowed to eat freely. Compared to the control group, all the male rats overate but in different ways. The dominant rats ate more frequently, gaining weight and lean mass, as compared to the control group. The subordinate rats ate larger meals, but less frequently, gaining significant fat in the visceral (belly) region.
During the whole recovery period, the subordinate rats continued to overeat, by eating longer meals and gaining fat, suggesting they experienced long-term, harmful metabolic changes.
Both animals and humans experience stress on a daily basis, and many individuals cycle through patterns of stress and recovery throughout the day. The study shows that if, following stress, individuals consume larger meals less frequently, the typical results are weight gain—especially in the abdomen. Stress, as well as belly fat, contributes to the development of cardiovascular disease, immune dysfunction and other disorders.
The study was conducted by Susan J. Melhorn, Eric G. Krause, Karen A. Scott, Marie Mooney, Jeffrey D. Johnson, Stephen C. Woods and Randall R. Sakai at the University of Cincinnati College of Medicine, Cincinnati, OH.