Protein and carbohydrates

Certain amino acids are effective secretagogues of insulin and have been found to synergistically increase the blood insulin response to a carbohydrate load when administered in combination (Floyd et al. 1966; Fajans et al. 1967). Of the 20 amino acids normally found in protein, the most effective insulin secretagogue is arginine (Fajans et al. 1967). When infused with carbohydrate, arginine has been found to increase the insulin response fivefold above that produced by the carbohydrate or arginine alone. However, we have found the use of amino acids to be impractical when added to a carbohydrate supplement because they produce many unwanted sideeffects such as mild borborygmus and diarrhoea. Protein meals and supplements also have been found to enhance the insulin response to a carbohydrate load and do not produce the unwanted side-effects of the amino acids (Rabinowitz et al. 1966; Pallota & Kennedy 1968; Spiller et al. 1987). For example, Spiller et al. (1987) demonstrated a nincreased blood insulin response and decreased blood glucose response with the addition of protein to a 58 g carbohydrate supplement. The insulin response was found to be directly proportional and the glucose response inversely proportional to the protein content of the
carbohydrate–protein supplement. No adverse side-effects were reported.



We therefore investigated the effects of a carbohydrate–protein supplement on muscle glycogen resynthesis after exercise (Zawadzki et al. 1992). The supplements tested consisted of 112g carbohydrate or 112g carbohydrate plus 40.7g protein (21% wt/vol mixture). The supplements
were administered immediately after exercise and 2h after exercise. It was found that the combination
of carbohydrate plus protein resulted in a synergistic insulin response. In conjunction with the greater insulin response was a significantly lower blood glucose response and a 38% faster rate of muscle glycogen storage compared with carbohydrate supplementation alone. Rates of muscle glycogen resynthesis averaged 7.1mmol·g–1 wet weight·h–1 for the carbohydrate–protein treatment and  5.0mmol·g–1 wet weight·h–1 for the carbohydrate treatment during the 4-h recovery period (see Fig. 7.5). It was also found that carbohydrate oxidation rates and blood lactate concentrations for the carbohy-drate–protein and carbohydrate treatments were similar. These results suggested that the
increased rate of muscle glycogen resynthesis during the carbohydrate–protein treatment was
the result of an increased clearance of glucose by the muscle due to the increased blood insulin
response. Since the carbohydrate–protein supplement was palatable and there were no unwanted side-effects, it would appear to be a viable supplement for postexercise glycogen recovery.