Eat To Grow: Postworkout Force-Feed

Recent studies document the importance of taking in both protein and carbohydrate shortly after training. It’s vital because protein synthesis doesn’t occur during training; it begins when the workout ends. Providing amino acids or a rapidly absorbed protein after your workout assists upgraded muscle-protein synthesis. You also need carbohydrates to provide raw material for muscle glycogen replenishment. Muscle glycogen is the primary fuel for anaerobic workouts, typified by bodybuilding training, and carbs, particularly high-glycemic-index, or simple, carbs, work best.

That’s because simple carbs promote the greatest insulin release. Insulin turns on the rate-limiting enzyme needed for muscle glycogen replenishment (glycogen synthase) while promoting muscle uptake of amino acids for more efficient muscle protein synthesis. Researchers found that a combination of protein and carbs constitutes the best nutritional recovery system following high-intensity exercise.

A few studies attribute the effectiveness of postworkout protein-and-carb drinks to a hormonal effect. For example, while carbohydrates alone promote insulin release, adding amino acids increases the release. That’s because some amino acids, termed glucogenic amino acids, are themselves capable of eliciting a potent release of insulin from the beta cells of the pancreas. Other studies show that carbs appear to blunt the rise of cortisol, a catabolic hormone secreted from the adrenal glands, during the late stages of a workout.

The latest study in that area compared various forms of postworkout meals for their effects on insulin, testosterone, cortisol and the testosterone-to-cortisol ratio.1 The subjects of the study included 10 experienced, weight-trained men, average age 20, who were given the following:

1) A whole-food meal, consisting of baked, skinless chicken breast and boiled long-grain white rice. The nutrient content of that typical bodybuilding meal was: protein, 38 grams; carbohydrate, 70 grams; fat, seven grams.

2) A special supplement drink designed for postworkout recovery that contained the same number of calories and protein as the meal described above. The supplement itself was a mixture of milk proteins, sugars and fat.

3) A carbohydrate beverage containing the same number of calories as the meal and drink. The carb sources were maltodextrin, a medium-acting source, and fructose, a long-acting source.

4) A placebo beverage containing three grams of carbs.

The subjects consumed one of the meals immediately after, then at two and four hours after training. They also had the whole-food meal at seven and 12 hours after training. The researchers measured various hormones before exercise and after 24 hours of recovery.

The results showed that the supplement drink led to the greatest increase in plasma insulin levels 30 minutes after the workout. The subjects also reported that it was easier for them to drink the drink shortly after training than to eat a solid-food meal. That’s likely because appetite is depressed for a short time following a workout, making it easier to ingest a drink than a regular meal.

While the carbs-only drink did promote an insulin release, the effect was greater with the supplement drink, which contained simple carbs and whey, a rapidly absorbed form of protein. Higher insulin levels are associated with increased muscle protein synthesis, decreased muscle catabolism, or breakdown, and blunted cortisol release.

Testosterone was depressed under all conditions for eight hours after exercise and returned to baseline levels 24 hours after training. Interestingly, those getting the placebo drink, which contained only tiny amounts of carbs, showed the least depression of testosterone following training. Apparently, eating anything tends to depress testosterone after a workout. This study also showed that when insulin levels are highest, testosterone levels are lowest and vice versa.

Cortisol, the primary catabolic hormone, rose after exercise and dropped below baseline levels 2 1/2 hours later under all feeding conditions. The cortisol levels were still depressed eight hours after training but returned to baseline by the 24-hour mark. According to the authors, that pattern of cortisol release mirrors the normal rhythmic release of the hormone, indicating that none of the meals had any effect on cortisol release.

The increased release of insulin by the supplement drink should have lowered cortisol levels, since insulin is known to oppose the activity of cortisol, yet that didn’t happen. The conclusion of this study was that meal composition following training had little effect on either testosterone or cortisol, both of which are more influenced by normal rhythmic release in the body. Even so, a supplement drink consisting of rapidly absorbed protein and simple carbs did promote an increase insulin secretion, which, in turn, is conducive to upgraded muscle tissue growth and muscle glycogen synthesis.

1 Bloomer, R.J., et al. (2000). Effects of meal form and composition on plasma testosterone, cortisol and insulin following resistance exercise. Int J Sports Nutr Metab. 10:415-24.