How much dietary protein does a bodybuilder require? Several organizations, such as the American College of Sports Medicine and the International Society of Sports Nutrition (shown in Figure 1), have recommended that physically active adults consume between 1.2-1.4 and 2.0 grams of protein per kilogram of bodyweight per day to allow for recovery from training and to promote the growth and maintenance of lean body mass. However, these recommendations are based primarily on studies that involve recreationally active or formerly untrained adults with normal amounts of lean body mass. Extending these recommendations to a resistance-trained bodybuilder looking to maximize lean body mass may not be appropriate.
Reference: Campbell et al. J Int Soc Sport Nutr. 2007 Sep.
Several studies have attempted to identify the minimal protein requirements of elite bodybuilders, novice bodybuilders, and strength-trained athletes. Using the nitrogen balance method, which attempts to determine protein requirements by measuring nitrogen intake and excretion, these studies suggested that protein requirements upwards of 1.4 grams per kilogram of bodyweight. However, the nitrogen balance method has several limitations, such as the way in which the data is analyzed (linear fits used for nonlinear data), inaccurate estimations of nitrogen intake and excretion, and the one to two week adaptation period required before protein intake measurements can be taken.
The last point is especially important, considering that athletes’ bodies can adapt to lower protein intakes over that adaption period. Isotope tracer studies have suggested that there are four stages of protein metabolism: deficiency, accommodation, adaptation, and excess. Nitrogen balance studies may show that people are in nitrogen balance at lower intakes of dietary protein because the body adapts to this lower amount by downregulating physiologically relevant pathways, like muscle protein synthesis and immune function. However, for a bodybuilder interested in maximizing muscle growth, this accommodation is not beneficial. Rather, the focus should be on conditions when both optimal growth and immune function are present.
The Indicator Amino Acid Oxidation (IAAO) technique is a method for determining protein requirements that overcomes many of the shortcomings of nitrogen balance studies. For instance, only a minimal adaptation period is required before testing of protein requirements. The IAAO method is based on the concept that when one essential amino acid is deficient for protein synthesis, then all other essential amino acids, including the “indicator” amino acid, will be oxidized for energy because protein cannot be readily stored like carbohydrate or fat (see figure 1 of ERD #19, Volume 1, How much protein does grandpa really need?). Dietary amino acids must be incorporated into bodily tissues via protein synthesis or oxidized for energy and excreted from the body.
The study under review used the IAAO technique to determine the protein requirements of young male bodybuilders. This is the first study to use the IAAO technique in this population, and will provide important information for helping to establish protein recommendations for bodybuilders while avoiding the shortcomings of nitrogen balance assessments.
Protein requirements of physically active adults remains a controversial area of research due to the widespread differences in people who are regularly active. Bodybuilders are one such population and have limited data available. Several studies have attempted to determine the protein requirements of bodybuilders using the nitrogen balance method, but nitrogen balance measurements have notable limitations. The purpose of the study at hand was to determine the protein requirements of bodybuilders using a method that overcomes many of the shortcomings of nitrogen balance research, called the Indicator Amino Acid Oxidation (IAAO) technique.