Weight loss in the elderly, specifically a decrease in lean mass, increases the risk of mortality significantly. A loss of skeletal muscle in the elderly is associated with reduced mobility, increased frailty, and a loss of bone tissue that increases the risk of fractures significantly. Skeletal muscle levels decline naturally with age as hormonal changes occur, but this decline can vary depending on a number of factors, the most important of which are diet and exercise. In the case of the latter, resistance type training where load is applied to the skeleton have been shown to be particularly beneficial in stressing the skeletal muscle and causing adaptive responses that include hypertrophy. For muscle growth to occur there is a requirement of a positive nitrogen balance, and this can only be achieved by adequate dietary protein intakes that supply enough essential amino acids in the correct ratios for tissue growth and repair. However, low protein intakes below the recommended levels are common in the elderly.
Therefore diet is an important factor in the maintenance of skeletal muscle in the elderly. Researchers have investigated the effects of higher protein diets on skeletal muscle mass in the elderly using observational studies. For example, in one study1, researchers used a prospective study of a large cohort of community dwelling elderly adults in order to assess their protein intakes in relation to their weight loss during a one year period. After adjusting for variables that are known to cause changes in skeletal muscle, the researchers reported that the odds of weight loss in subjects with a low protein intake of less than 0.8g per kg body weight per day compared to a high protein intake of greater than 1.2 grams per kg body weight per day almost doubled. Those with a moderate protein intake (0.8 to 1 g per kg body weight per day) and high intake (1.0 to 1.2 grams per kg body weight per day) also had significantly higher odds of experiencing weight loss, compared to those with very high protein intakes.
Therefore elderly individuals with lower protein intakes have a significantly increased chance of sustaining weight loss compared to those with a higher intake. The lower intakes of protein in the elderly are not surprising because diet quality and energy intakes tend to decline with age. Therefore the risk of the elderly succumming to a negative nitrogen balance is increased compared to younger individuals. Interestingly the effects of protein on weight loss in this study were independent of the energy intake of the subjects. The mean protein intake in this study was around 16 % which is low compared to the recommended intake for protein and the amount often used in moderate to high protein diets in order to promote body composition improvements in younger healthy subjects. The authors suggested that evidence supports the notion that the recommended protein intakes should be increased in the elderly in order to prevent reduction in lean mass seen with increasing years through increases in nitrogen retention.