Many protein-supplement ads boast of their product having little or no carbohydrate content. Yet scientists have known for decades about
the nutritional synergy between protein and carbohydrates. In short, carbs have a protein-sparing action. The body favors carbs as an energy
source, but when curbs are either drastically reduced or eliminated from the diet, the body taps its next most available energy source:
This protein can be derived from either food or, in the case of insufficient protein intake, muscle tissue. The liver easily converts amino acids into glucose through a process called gluconeogenesis. In contrast, bodyfat is like seawater to a marooned sailor; there's plenty of it, but it's of little use.
Only 10% of triglyceride, the chemical name for bodyfat, is available for glucose production in the liver. Adequate consumption of carbs, however, spares protein as an energy source, freeing it for use in tissue repair, hormone synthesis and all the other wonderful things associated with protein. But less well known about the relationship between carbs and protein is the direct effect carbs have on intestinal amino-acid retention after a meal. This effect relates to the limitations the body has in absorbing protein following food intake.
Scientists recently examined this process of amino-acid retention in pigs who had just eaten a meal. The study, reported in the Journal of Nutrition (14:354-364, 1995), which used high-quality whey as the protein source, indicates that pigs apparently process food protein in a manner similar to humans. These pigs were studied for six hours after eating meals consisting of either protein with carbs, pure protein or a control meal. Adding carbs to the protein meal resulted in an increased glucose release in the gut, which in turn led to increased insulin levels in the blood. The amino acids in the portal blood (gut vessels) dropped 30% in spite of the 95% digestibility of the protein meal. The portal system normally shuffles amino acids to the liver, where they ore rapidly metabolized into protein waste products for elimination.
However, due to the lower amounts of aminos in the portal blood due to the carb/insulin reaction, fewer aminos went to the liver, resulting in far less protein wastage. After the protein/carb meal, the blood concentrations of most amino acids were considerably higher compared to the outcomes researched after the pure protein meal.
These results suggest that carbs are a vital mediator in increased protein retention via gut mechanisms. Combining carbs and protein in the same meal leads to a slower release of amino acids, which reduces protein wastage.