Volume 81, Number 2 March/April 2010
With a growing elderly population in the U.S., age-related degenerative disorders such as sarcopenia and osteoporosis are receiving increased attention. Sarcopenia, the progressive loss of muscle, is associated with reduced strength and functional impairment in older adults. Osteoporosis, a disease characterized by low bone mass, leads to bone fragility and increased susceptibility to fractures. Multiple factors, genetic and environmental, contribute to these disorders. Accumulating research suggests that increased intake of high-quality protein may help preserve older adults’ muscle and bone mass.
The current Recommended Dietary Allowance (RDA) for protein is 0.8 g/kg body weight/day for adults aged 19 years and older. The RDA is defined as a minimum amount to prevent deficiency, not an optimal amount to promote health. The RDAs for protein are based on nitrogen balance studies primarily conducted in young men. These issues, along with general limitations of the nitrogen balance technique, have led some scientists to call for a re-evaluation of the protein RDA for older adults.
Intake of dietary protein stimulates muscle protein synthesis by increasing the availability of amino acids, specifically essential amino acids (EAAs). It is generally accepted that fasting rates of muscle protein synthesis do not differ substantially between young and older adults. However, with aging there often is a decrease in voluntary protein and energy intakes, as well as a blunted response to anabolic stimuli (e.g., mixed meals containing protein, amino acids) that compromise the ability to build and repair muscle tissue. New research indicates that this blunted response can be overcome in older adults by moderately higher intakes of protein or EAAs. Specifically, the research suggests that consuming approximately 25 to 30 g of high-quality protein at each meal may maximize muscle protein synthesis producing comparable increases in muscle protein synthesis rates in young and older adults.
Intake of dietary protein stimulates muscle protein synthesis by increasing the availability of amino acids, specifically essential amino acids (EAAs). It is generally accepted that fasting rates of muscle protein synthesis do not differ substantially between young and older adults. However, with aging there often is a decrease in voluntary protein and energy intakes, as well as a blunted response to anabolic stimuli (e.g., mixed meals containing protein, amino acids) that compromise the ability to build and repair muscle tissue. New research indicates that this blunted response can be overcome in older adults by moderately higher intakes of protein or EAAs. Specifically, the research suggests that consuming approximately 25 to 30 g of high-quality protein at each meal may maximize muscle protein synthesis producing comparable increases in muscle protein synthesis rates in young and older adults.
Findings also indicate that there may be a beneficial effect of increased protein intake on older adults’ bone health and that low protein intakes may be detrimental to bone. Protein may positively contribute to bone health by providing amino acids as substrates for building bone, by stimulating the production of insulin-like growth factor-1 which is important for bone mineralization, and by maintaining muscle mass in later years. Protein’s effect on bone mass depends on other nutrients such as calcium. Increasing protein intake has been demonstrated to increase bone mineralization in older adults consuming recommended intakes of calcium and vitamin D.
Scientific evidence suggests that a protein intake moderately higher than the current RDA of 0.8 g/kg/day may help support muscle and bone health in the elderly. Consuming nutritionally balanced diets including foods providing high-quality protein such as low-fat and fat-free milk, cheese, or yogurt, as well as foods and beverages incorporating whey protein can help meet older adults’ protein needs.
Next page »
Table of Contents: