Protein intake and muscle function in older adults

Abstract

Purpose of review We provide an update on the recent advances in nutrition research regarding the role of protein intake in the development and treatment of sarcopenia of aging. Recent findings Specific muscle mass, strength and function cutpoints for the diagnosis of sarcopenia have been identified. There is mounting evidence, as highlighted by multiple consensus statements, that the RDA (0.8g/kg BW) may be inadequate to promote optimal health in older adults. Recent research also indicates that in addition to total daily protein intake also the timing of protein intake is important to best stimulate muscle protein synthesis and maintain muscle mass and function in older adults. Summary Recent evidence suggests that the RDA for protein is inadequate and that the timing and distribution of protein consumption throughout daily meals may be as important as the total quantity. Research has continued to advance our understanding of protein’s effects on muscle metabolism; however, there remains a need for large, long-term, randomized clinical trials examining whether the positive effects of dietary protein on muscle metabolism seen in acute studies will translate over the long term into gains of muscle mass, function, and overall health of older adults.

Protein Intake and Disability Trajectories in Very Old Adults: The Newcastle 85+ Study

“…For example, 28% of very old adults in northeast England had protein intake below the recommended dietary allowance (RDA) of 0.8 g per kg of adjusted body weight per day (g/kg aBW/d) . Furthermore, the greater incidence and prevalence of multimorbidity in older adults can change protein requirements because of disease‐related tissue catabolism and inflammation . The current protein RDA for all adults is based largely on short‐term nitrogen balance studies conducted in healthy young adults and does not take into account functional outcomes, such as disability .…”

Identifying effective and feasible interventions to accelerate functional recovery from hospitalization in older adults: A randomized controlled pilot trial

“…However, most studies investigating the potential benefits of these treatments have been tested in healthy older adults [28–30, 32–34]. We have previously conducted mechanistic-based studies demonstrating that: 1) aging attenuates the meal stimulated increase in skeletal muscle protein synthesis [50], 2) anabolic resistance of skeletal muscle to nutrients with aging is associated with endothelial dysfunction and blunted mammalian/mechanistic target of rapamycin complex 1(mTORC1) signaling [51, 52], 3) acute exercise improves endothelial function and muscle perfusion, and enhances skeletal muscle protein synthesis after nutrient ingestion in older adults [31–34], 4) older adults require more amino acids (or protein) than younger individuals to stimulate skeletal muscle protein synthesis [28–30], 5) the response of skeletal muscle protein synthesis to essential amino acids depends on a high leucine dose (~3 g) with maximal stimulation occurring when ingesting approximately 30 g of whole protein per meal [29, 53–55], 6) inactivity (short-term bedrest) blunts skeletal muscle mTORC1 activation by amino acids, increases anabolic resistance of skeletal muscle, and is associated with reduced skeletal muscle amino acid transporter expression in older adults [56–58] and 7) muscle anabolism in response to resistance exercise is reduced in older adults but this problem is mitigated by protein intake after the exercise bout. These data show that, relative to younger individuals, older adults require more protein and physical activity to achieve an anabolic response in skeletal muscle.…”

“…However, these previous studies have not observed benefits of protein supplementation on measures of physical function or muscle size. A limitation of many of the previous studies is that subjects were not provided or did not consume a sufficient amount of protein in a given meal [30, 67, 68]. The inadequate distribution of protein might have reduced the benefits of protein supplementation on muscle strength and function [69, 70].…”

“…The inadequate distribution of protein might have reduced the benefits of protein supplementation on muscle strength and function [69, 70]. Older adults require a greater amount of protein, in particular the amino acid leucine, than younger individuals to adequately stimulate muscle protein anabolism [29, 30, 54, 71–75]. One clinical trial carried out in frail, yet otherwise relatively healthy, older adults has reported that adequate doses of high quality protein throughout the day (15 g protein supplement at breakfast and lunch) can increase measures of physical function [76].…”

A Geriatric Exercise Program May Yield Multiple Benefits

“…At final follow‐up, total calorie and carbohydrate intakes had decreased in the intervention group, whereas protein intakes had increased in the control group. Timing of meals relative to training sessions was not evaluated; addressing this element may be important to optimize muscle protein synthesis for improving and maintaining lean mass and physical function …”