Trainers often don’t insist that their clients take in enough amounts of complete protein (one that contains all amino acids). Their argument is that only serious body builders need to worry about protein. Modern scientific evidence says that foods rich in complete protein contain an amino acid called tyrosine, which boosts two brain chemicals that elevate mood. Protein improves concentration, besides repairing the damage caused to muscle tissue. Complete protein is found in egg whites, skimmed milk, chicken breast (grilled), tuna and supplements such as whey protein powder.