Dietary supplement
According to US & Canadian Dietary Reference Intake guidelines, the protein Recommended Dietary Allowance (RDA) for adults is based on 0.8 grams protein per kilogram body weight. The recommendation is for sedentary and lightly active people. Scientific reviews can conclude that a high protein diet, when combined with exercise, will increase muscle mass and strength, or conclude the opposite. The International Olympic Committee recommends protein intake targets for both strength and endurance athletes at about 1.2-1.8 g/kg body mass per day. One review proposed a maximum daily protein intake of approximately 25% of energy requirements, i.e., approximately 2.0 to 2.5 g/kg.
Soy protein
When measuring the nutritional value of protein, the original protein efficiency ratio (PER) method, first proposed by Thomas Burr Osborne and Lafayette Mendel in 1917, was the most widely used method until 1990. This method was found to be flawed for the biological evaluation of protein quality because the young rats used in the study had higher relative requirements for sulfur-containing amino acids than did humans. As such, the analytical method universally recognized by the FAO/WHO (1990), as well as the FDA, USDA, United Nations University and the National Academy of Sciences when judging the quality of protein is the protein digestibility-corrected amino acid score, as it is viewed as accurately measuring the correct relative nutritional value of animal and vegetable sources of protein in the diet.
Based on this method, soy protein is considered to have a similar equivalent in protein quality to animal proteins. Egg white has a score of 1.00, soy concentrate 0.99, beef 0.92, and isolated soy protein 0.92. In 1990 at an FAO/WHO meeting, it was decided that proteins having values higher than 1.0 would be rounded or "leveled down" to 1.0, as scores above 1.0 are considered to indicate the protein contains essential amino acids in excess of the human requirements.