Muscle mass typically declines with older age
The aging US population faces increased risk of sarcopenia, the progressive loss of muscle mass and strength, and frailty. Sarcopenia predicts higher mortality, lower Quality of Lifespan, reduced independence, and greater inability performing activities of daily life. Thus, identifying practical ways to maintain muscle mass and strength in older people could have major positive personal and public health consequences.
Muscle strength greatly affects the ability of older people to accomplish activities of daily living. How much does muscle strength change with time in older people? Researchers measured knee and elbow flexor and extensor muscle strength of 190 older adults with an average age of 60 years. Ten years later, 120 members of the original group were re-tested. For men and women combined, the strength of knee extensor and flexor muscles declined by an average of 14 and 16 percent, respectively, over ten years. That notwithstanding, some participants increased their knee flexor or elbow flexor strength over 10 years, as much as 32 percent for women and 13 percent for men. Thus, advancing age does not automatically signal loss of knee or elbow flexor muscle strength. This group of older people was relatively active compared to typical Americans, who might have exhibited even greater average losses in knee and elbow muscle strength.
Does the recommended daily allowance for protein apply to seniors?
Some researchers have suggested that the recommended daily dietary intake of protein should be increased. A study that used data from 2,066 community-dwelling adults with an average age of 74 years in Pittsburgh, PA, and Memphis, TN, addressed this matter. Diet was assessed using an interviewer-administer food-frequency questionnaire during year 2 of the 3-year study. Researchers used dual x-ray absorptiometry data to determine total lean (non-fat) mass and lean mass of arms and legs. On average, participants ate slightly more daily protein (0.9 grams / kg of body weight) than the recommended daily allowance (RDA, 0.8 grams / kg of body weight). After adjusting for confounding factors, higher daily protein intake predicted greater total lean mass and greater leg and arm lean mass. This relationship arose from animal protein but not vegetable protein intake. Compared to participants in the lowest quintile of protein intake (59 grams per day), participants in the highest quintile (91 grams per day) lost significantly less total lean mass and leg and arm lean mass over three years of follow-up. Participants who gained body weight during follow-up also gained significant lean mass, while participants who lost body weight lost significant lean mass.
Seniors may need at least 1.2 grams of protein per kg of body weight per day
Researchers in Canada and the US used radioactive amino acid, phenylalanine, to follow the rate of muscle (myofibrillar) protein synthesis in 43 healthy older (average age 71 years) and 65 healthy younger (average 22 years) men in a laboratory. Varying amounts of easily digestible animal protein with radioactive phenylalanine were administered followed 3-4 hours later by muscle biopsy. After adjusting for body mass, the rate of muscle protein synthesis stopped increasing at 0.24 grams protein per kg of body weight for younger men and at 0.4 g protein per kg of body weight for older men. Thus, older men needed more protein intake to maximize the rate of muscle protein synthesis. These findings suggest that, for a 75 kg (165 lb.) older man, such as yours truly, animal protein intakes of 30 grams at each of three daily meals (90 grams per day) would optimize muscle protein synthesis
Declines in skeletal muscle mass and strength are major contributors to increased mortality, morbidity and reduced quality of life in older people. Recommended dietary allowance for protein does not adequately consider the needs of elderly with regard to maintaining muscle mass and function. Current recommended protein intakes for older people do not account for the compensatory loss of muscle mass that occurs on lower protein intakes. Older people have lower rates of muscle protein synthesis in response to eating protein (or to resistance exercise). Randomized controlled trials show a clear benefit of increased dietary protein on increased muscle mass and leg strength, particularly when combined with resistance exercise. Consistent evidence favors consumption of 1.0 to 1.3 grams of dietary protein per kg of body weight combined with twice-weekly progressive resistance exercise to reduce age-related muscle mass loss.
A more recent review also found that older people likely need considerably more that the current recommended daily allowance of protein (0.8 grams per day). This increased need arises from lower ability of older compared to younger people to convert dietary protein into muscle protein. The review found no merit in the idea that higher protein intakes would lead to kidney problems. Leucine, an essential amino acid, appears to be especially important in stimulating muscle synthesis. The authors of this review recommend at least 1.2 grams of protein per kg of body weight per day for older people. Older people should favor leucine-rich foods such as salmon, chickpeas, brown rice, eggs, nuts, and soybeans.
A new, short narrative review found that the preponderance of the evidence supports the effectiveness of older adults increasing daily protein intake (1.0-1.6 grams per kg of body weight per day) to build muscle mass or reduce its loss – but only for certain persons. The benefit of increasing protein intake beyond the recommended daily allowance occurs when accompanied by resistance exercise training. The benefit may also accrue for older adults with diagnosed medical conditions. Finally, a benefit would likely occur for the substantial fraction of older Americans that under-consumes protein-rich foods and may not consume enough protein to reach the RDA. On a per weight basis, animal protein likely provides a greater protein synthesis response than plant protein.
How much protein in a single meal?
Researchers in Arkansas reviewed evidence regarding protein intake for older people. Research suggests that protein intake is a crucial aspect of maintaining muscle mass and avoiding sarcopenia. Alas, older people respond less to dietary protein in terms of muscle protein synthesis than younger people. This finding points toward older people consuming more protein than younger people to maintain muscle mass. Research by the authors of the review suggests that daily intake of between 1.2 and 2.0 grams of high-quality protein per kg of body weight will stimulate maximum muscle protein synthesis. Contrary to other authors, these authors do not find an upper physiological limit to daily protein intake as it relates to muscle protein synthesis. Thus, they disagree with the idea of spreading daily protein intake into three more or less equal amounts each day.
A recent review summarized the controversy that exists regarding how much protein in a single meal can be used to build muscle. Much of the relevant research has focused on body-builders who want to add muscle mass. One idea is that muscle protein synthesis maxes out with 20-25 grams of protein consumed shortly after a weight-training session. Other findings suggest that 0.4 grams of protein per kg of body weight optimally foster muscle protein synthesis. For me, at 75 kg of body weight, that translates to 30 grams of whey protein at each training session. According to the authors of the review, the current evidence supports a target intake of protein of 0.4 grams per kg of body weight four times daily or 1.6 grams protein per kg per day, twice the RDA. For me, this translates to 120 grams of protein per day. Because I’m not a body-builder, I probably don’t need that much protein.
What to do?
Based on this and other studies, I've increased my daily protein intake to about 1.2 grams / kg of body weight or about 90 grams per day. My daily protein intake comes largely from low-fat Greek yogurt, whey powder, peanut butter, soy milk, cow’s milk, and beans. Plus, I head to the gym twice each week for one hour of resistance exercise training. I believe that the combination of boosting my daily protein intake and resistance exercise training will allow me to continue my long-distance hiking and cycling adventures.
