05 May 2012

Nevermind body fat; put focus on muscle with age

With all the attention given to body fat, a result of the high prevalence of obesity and type 2 diabetes, skeletal muscle is often given the back seat. Yet holding on to lean muscle mass alone, in itself, may be the most important factor in avoiding health problems above. What's often forgotten is that skeletal muscle is a metabolically active tissue that plays a critical role in consuming energy and determining metabolic rate, it's the large site for fat burning, and it's a primary site for blood glucose disposal. It's time to give muscle its due.

When you reach age 60 or older, it gets harder to keep, let alone build, muscle. The reasons are a combination of lack of energy, exercise, dietary protein, and hormones. One more is a blunted protein synthesis response that is described as anabolic resistance in aging. Left to run their course, these factors eventually bring on a decrease of muscle mass over time, or sarcopenia. The loss is also often accompanied with an increase in fat mass, or sarcopenic obesity. Sarcopenic obesity brings along with it the lack of both mobility and physical function, with compounding effects, that eventually lead to increased risk of chronic disease.

The typical recommendations for adults as they lose muscle and gain weight by nutritionists is to simply exercise at least 30 minutes three times a week, eat fewer calories, and get the recommended daily intakes of protein (0.8 g per kg). But this advice has had little to offer for guarding against the heavy toll that time has on muscle. However, in the last few hours of Experimental Biology 2012 on April 25, I was fortunate enough to meet a scientist who gave a lecture on a different approach to overcoming anabolic resistance in aging.

 Kinesiologist Stuart Phillips, a professor McMaster University, is a lifelong athlete who has participated in several sports enjoying everything from hockey, football, rugby to swimming and triathlons. "Muscle has always been near and dear to my heart (no pun) and my passion," he told me via email after the event. "I don’t compete in sports much anymore except with my wife and my three boys (13, 10, and 7), who are my stiffest competition yet! So now it's about staying healthy, active, and maintaining my muscle mass, strength, and health and high-quality protein is a big part of that."

Anabolic resistance, as Phillips defines it, "is the inability of skeletal muscle in aged persons to mount a full protein synthetic response similar to that seen in the young. In other words, older people just don’t put the protein they eat into their muscles as efficiently as young people. That means as we age that our muscles gradually begin to make less protein and so out muscle mass declines otherwise called sarcopenia." But according to Phillips, the quality of protein and how much can make all the difference for holding on to muscle with age. Specifically proteins with a higher concentration of branched-chain amino acids including leucine are key to repairing and gaining muscle with age. That means a greater reliance on animal-sourced proteins like whey protein. Plant-based sources just don't cut it because of the difference in amino acid profile. Now, there's something to think about before ever considering a completely plant-based diet.

Phillips explains, for example, that soy is an excellent high quality protein as its PDCAAS (protein-digestibility corrected amino acid score) would suggest. But whey is superior for repairing and gaining muscle, as shown in several studies (1-4). Even milk protein (containing a combination of whey and casein) is better than soy for promoting lean mass gain (2; 3).

 "Our work, and that of other research groups also, suggests that it's the high leucine content of whey protein, which is an amino acid that is highly stimulatory for muscle protein synthesis and muscle growth," Phillips told me, "that along with all of the other ‘essential' (i.e., we need to eat them because we cannot make them ourselves) amino acids are present in just the right quantities to support an optimal rate of protein accretion."

Adults at an age past 60 will also need dietary protein in amounts that exceed RDIs, Phillips adds. Consuming greater quantities of proteins high in leucine such as whey can help aging adults "'overcome' (or at least minimize)" the anabolic resistance of aging and slow sarcopenia. "I'd never say you could reverse sarcopenia, but good food choices and good high-quality proteins, along with physical activity, are a big part of slowing it down!"

Exactly how much protein per day and when to get it? According to two dose-response studies by Phillips and his colleagues (5;6) young men required 20g of quality protein to maximally stimulate muscle synthesis after exercise; older men needed approximately double the dose, 40g, to gain the same maximal stimulation. That, Phillips thinks, suggests that the young should eat at least 20g per meal and older people 40g per meal.

 This is a far cry from the typical American diet of which usually consists of about 5-6g of protein at breakfast, 10-12g at lunch, and upwards of 60g at dinner. "That’s not the best way to hang onto your muscle mass," Phillips said.

 Exercise certainly is an important factor, too. Because it increases the sensitivity to leucine in muscles, Phillips suggests that it be physical activity needs to happen every day in aging adults. "In a sense, exercise, for a short-time, 'reverses' aging! In fact, what it really does is reverses the effects of inactivity, but oftentimes aging and inactivity are one and the same! So even aged muscle, when exercised, becomes sensitive to leucine and amino acids again." 

Summing up his advice, Phillips offers four steps to keep muscle (again, a critical metabolically active tissue), important to guard against sarcopenic obesity and chronic disease:
  1. "Exercise and get some form of physical activity every day"
  2. "Consume protein at levels higher than the current RDA" 
  3. "Consume three equal protein-containing meals throughout the day containing at least 20g to 40g of high-quality protein" -- high quality meaning proteins high in BCAAS like whey, fish, or other animal-sourced proteins; simply put, most plant-based proteins have poor concentrations of BCAAs 
  4. Lastly, "it should maybe go without saying, but fruits, vegetables, and dietary fiber are also important – I like the DASH [eating plan], for example, but with more protein." -- a DASH (Dietary Approaches to Stop Hypertension" eating plan is a diet rich in low-fat, low-sodium dairy products, fish, chicken, lean meats along with a large amount of whole grains, fruits, and vegetables. 
Ultimately, the research of Phillips and his colleagues could have large implications considering that the world's population of people ages 60 and older will reach an estimated two billion people by 2050 -- all who could benefit from holding on to muscle as long as possible.  

References provided by Dr. Phillips 

  1. Burd NA, Yang Y, Moore DR, Tang JE, Tarnopolsky MA and Phillips SM. Greater stimulation of myofibrillar protein synthesis with ingestion of whey protein isolate v. micellar casein at rest and after resistance exercise in elderly men. Br J Nutr 1-5, 2012. 
  2. Hartman JW, Tang JE, Wilkinson SB, Tarnopolsky MA, Lawrence RL, Fullerton AV and Phillips SM. Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters. Am J Clin Nutr 86: 373-381, 2007. 
  3. Josse AR, Tang JE, Tarnopolsky MA and Phillips SM. Body composition and strength changes in women with milk and resistance exercise. Med Sci Sports Exerc 42: 1122-1130, 2010. 
  4. Tang JE, Moore DR, Kujbida GW, Tarnopolsky MA and Phillips SM. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol 107: 987-992, 2009. 
  5. Moore DR, Robinson MJ, Fry JL, Tang JE, Glover EI, Wilkinson SB, Prior T, Tarnopolsky MA and Phillips SM. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr 89: 161-168, 2009.

  6. Yang Y, Breen L, Burd NA, Hector AJ, Churchward-Venne TA, Josse AR, Tarnopolsky MA and Phillips SM. Resistance exercise enhances myofibrillar protein synthesis with graded intakes of whey protein in older men. Br J Nutr 1-9, 2012.

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