Inadequate protein intake has been shown to be related to the age-related decrease in muscle mass. The American College of Sports Medicine (ACSM) suggests that older non-athletes need approximately 0.9 grams or protein per kilogram of body weight per day (g/kg/d). However, the current Recommended Dietary Allowance (RDA) in the United States is 0.8 g/kg/d with this figure based on the needs of young people.
Older athletes of any age have increased protein requirements due to the need for repair of the damage that training and competing have on muscle fibres, as well as the increased use of protein as an energy source, particularly in aging endurance athletes, and the need for increased protein to support increases in muscle mass that generally accompanies increased training intensities or weight training.
Insufficient overall dietary energy intake can lead to a protein loss given that there is a well-defined interaction between total energy intake and protein need. Moreover, increased protein requirements have been observed with high versus low intensity exercise and long versus short duration exercise. Thus, it has been suggested that younger endurance-trained athletes in regular training consume about 1.2-1.4 g/kg body mass/day (150% of current US RDA) and young strength-trained athletes 1.6-1.7 g/kg body mass/day (200% of current US RDA).
Older endurance or power athletes may require a lower protein requirement than suggested above for a number of reasons. First, the aging process is accompanied by a decline in muscle mass in both healthy active individuals and masters athletes secondary to an age-related decrease in both whole-body protein turnover and protein synthesis. Secondly, older athletes appear not to train with the same intensity and/or volume as younger athletes. Thirdly, although not conclusively investigated in masters athletes, there may be an age-related reduction in the absorptive capacity of the gut for amino acids. Fourthly, due to a number of underlying problems (dietary recall problems or inadequate energy intakes given by researchers in protein studies), the protein requirements suggested in the RDAs may have been overestimated. Taken together, the above factors suggest that older athletes may require a lower daily protein intake than those suggested above for younger athletes.
Thus, although the protein needs of different aged athletic populations is not considered, it has recently been suggested that aging exercisers may require 0.8-1.0 g/kg body weight/day with one leading researcher suggesting older exercisers may require 1.0-1.25 g/kg body weight/day in order to promote a positive protein balance. Adjustments may have to be made for illness, chronic disease, or suboptimal total energy intakes. This figure of 1.0-1.25 g/kg body weight/day approximates the observed protein intakes of 1.25-1.45 g/kg body weight/day observed in older athletes and regular exercisers from a variety of training backgrounds. However, older athletes in heavy training, particularly those involved with strength and power sports, may require increased protein intakes (e.g. 1.5-1.7 g/kg body weight/day) since resistance exercise increases muscle protein synthesis in both elderly and young individuals.