Cortisol is a hormone produced by the adrenal glands in response to stress, such as the physical stress of exercise. Cortisol is one of a group of hormones referred to as glucocorticoids. These hormones are named for their effects on glucose production. Among its effects, high cortisol levels stimulate your liver to convert amino acids into glucose to create a ready supply of energy for your cells to deal with increased stress. Scientists have studied the intricate effects of carbohydrate consumption on cortisol levels under various conditions.
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Testosterone to Cortisol Ratio
A low-carbohydrate diet decreased the ratio of testosterone to cortisol in male athletes in a study conducted by the department of exercise and sport science at the University of North Carolina, Chapel Hill. The testosterone-to-cortisol ratio is used as a gauge for overtraining and stress. In the study, participants who ate a low-carbohydrate diet -- containing approximately 30 percent calories from carbohydrate -- and performed intensive training showed lower testosterone-to-cortisol ratios at the end of the four-day study period. Results indicate a potential elevation in cortisol occurring from the low carbohydrate intake. The study was published in the April 2010 issue of the "European Journal of Applied Physiology."
Researchers at the department of human biology, Maastricht University, Netherlands, reported that cortisol levels decreased in the 3 hours following high-protein and high-fat meals and increased in response to a high-carbohydrate meal in obese study participants, over four consecutive days. The researchers concluded that protein and fat decreased the cortisol response but that adding carbohydrate prevented a drop in cortisol. The study was published in the December 2010 issue of the journal "Physiology and Behavior."
High-carbohydrate consumption decreased cortisol response but did not reduce oxidative stress in endurance athletes in a study conducted at the department of health, leisure and exercise science at Appalachian State University, Boone, North Carolina. Similarly, stress hormones known as catecholamines are decreased by carbohydrate consumption. These hormones can become oxidized when they accumulate to high levels, leading to production of dangerous free radicals. In the study, conditioned marathon runners ran for 3 hours at 70 percent of their maximum aerobic capacity while drinking carbohydrate-containing fluids. Post-exercise cortisol levels were significantly lower in the carbohydrate group than in a control group; however, the level of oxidative stress was the same between the two groups, implying that carbohydrate supplementation during intense exercise decreases levels of stress hormones but may not protect against oxidation effects of the exercise.
Decreased Muscle Damage
A study conducted by the School of Human Movement Studies, Charles Sturt University, Bathurst, Australia found that a carbohydrate meal decreased cortisol levels by 11 percent and a carbohydrate meal with amino acids decreased cortisol levels by 7 percent in a group of untrained young men. In the study, participants consumed the meals during sessions of weight-lifting. By contrast, a control group that consumed a meal that did not contain high quantities of carbohydrate showed a 105 percent increase in cortisol levels. The high-carbohydrate meal also decreased, by as much as 27 percent, the degree of muscle tissue damage incurred from the exercise. The study was published in the May 2006 issue of the journal "Metabolism."