For centuries, protein was considered the staple of the diet and the source of speed and strength for athletic endeavors. Although we now know that carbohydrates are the main energy source for humans, protein remains a main nutrient of interest, especially among bodybuilders, weightlifters, and others who engage in resistance training.
When answering the question “How much protein does my client need?” the personal trainer must consider two key factors, energy intake and source of protein. Protein may be used for energy when fewer calories are consumed than are expended. If this is the case, protein intake will not be used solely for the intended purpose of building and replacing lean tissue. Thus, when caloric intake goes down, the protein requirement goes up. Dietary protein requirements were derived from research on subjects who were consuming adequate calories. Requirements for clients who are dieting for weight loss are higher than standard requirements.
Additionally, protein requirements are based on “reference proteins” such as meat, fish, poultry, dairy products, and eggs, which are considered high-quality proteins. If protein in the diet comes mostly from plants, the requirement is higher. The U.S. Recommended Dietary Allowance (RDA) for protein for healthy, sedentary adults is 0.8 g/kg of body weight for both men and women (31). The World Health Organization identifies the safe intake level, a level that is sufficient for 97.5% of the population, at 0.83 g protein/kg per day. The safe level ensures a low risk that needs will not be met but also includes the concept that there is no risk to individuals from excess protein intake up to levels considerably higher than 0.83 g/kg (51). Though the intake set by both of these organizations may be sufficient for nonactive healthy, young adults, it is not appropriate for clients who have greater protein needs to help offset protein–amino acid oxidation during exercise, repair muscle damage, and build lean tissue. A general recommendation for athletes is 1.2 to 2.0 g/kg per day depending on the sport, training intensity, total calorie intake, and overall health (10).
The personal trainer should be aware that excessively high protein intakes (e.g., greater than 4 g/kg body weight per day) are not indicated for clients with impaired renal function, those with low calcium intake, or those who are restricting fluid intake. These situations could be exacerbated by a high protein intake. For the most part, however, concerns about potential negative effects of high protein intakes are unfounded, especially in healthy individuals. Proteins consumed in excess of amounts needed for the synthesis of tissue are used for energy or are stored.