Some scientists believe that while amino acids ore involved in muscle-protein synthesis, certain anabolic hormones must be present at the same time for the synthesis to work efficiently. However, a new study, reported in the American Journal of Physiology (34:E718-E724, 1996), found
that amino acids don't need the hormonal partnership of insulin and insulin like growth factor-I (IGF-l) to do the job. The study, which used normal human subjects, found that amino-acid infusions increased protein synthesis and prevented protein breakdown in arm and leg muscles.
There were some interesting aspects of this study: 1. No changes occurred in levels of either IGF-l or insulin during the infusions, and 2. the amino-acid mixture used was balanced in essential amino acids, which suggests that the body can supply recirculated amino acids (aminos already present) to make up for amino-acid deficiencies. The latter effect is similar to what occurs in vegetarian diets. Past advice concerning such diets suggested using "complementary" proteins; that is, combining foods lacking in different essential amino acids, so that one protein food could make up far the deficiencies of another consumed during the same meal.
At the time this concept was developed, it was believed that all essential amino acids had to be present simultaneously for optimal protein absorption. later studies using sophisticated isotope-labeled amino acids found that consuming all of the essential amino acids at the same time wasn't necessary due to the existence of an amino-acid pool in the body that could supply missing aminos according to need. The advice given to vegetarians was subsequently changed: They were advised to eat a variety of foods over the course of a day in order to eventually supply oil required amino acids, some of which were added to the amino-acid pool.
The message of the new study reported here is that amino acids themselves promote increased muscle protein synthesis while simultaneously retarding muscle-protein breakdown. Producing an optimal anabolic effect requires eating frequent protein meals throughout the day, spaced no more than three hours apart.