Protein preserves your muscles
Dairy products are rich in protein, along with lean meat and poultry, fish, seafood, eggs, nuts and seeds, beans and soy. (Fotolia.com / December 5, 2012)
Some muscle mass loss with aging is inevitable, but that doesn't mean you have to end up with sarcopenia, a condition in which loss of muscle mass is associated with a decline in muscle function, according to Roger Fielding, Ph.D., director of the Nutrition, Exercise Physiology, and Sarcopenia Laboratory under the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University.
Not surprisingly, experts advise adequate protein intake as part of a balanced diet and exercise, with a focus on strength training, to manage or prevent sarcopenia. Is avoiding sarcopenia that simple? To find out, EN explores the science behind muscle mass and function loss, and provides answers to common questions about how to preserve your muscles as you age.
HOW MUCH MUSCLE DO YOU LOSE?
We know from observing elite athletes as they age that they experience declines in performance, telling us that some muscle loss occurs in our 30s and 40s. Yet, how much we lose is unclear. Population studies reveal that at around age 50, muscle mass loss averages one to two percent per year.
We may not notice acute losses, because "muscle is a dynamic tissue, and there's a tremendous reserve capacity," says Fielding. "If you simply lose muscle mass, it may have very little impact on your body's ability to function. In your early 60s, we start to see that this loss may begin to affect physical ability." This makes sense, given muscle strength declines at an average rate of three percent per year after 60, and by our 70s we've lost an estimated 20 to 40 percent of our strength.
Why do you lose muscle mass and strength? Activity and dietary patterns play important roles in muscle maintenance, but they don't paint the whole picture. Natural physiological shifts take place during aging that correlate to declines in muscle health, including the following:
1. Loss of nerve cells that tell the brain to move your muscles. Fast-twitch muscle fibers, which give you strength and mass, become smaller and fat infiltrates into the muscle.
2. Hormonal changes associated with muscle loss. Men lose testosterone, women lose estrogen, and both lose growth hormone and insulin-like growth factor.
3. Vascular changes. Blood vessel function becomes impaired, affecting the delivery of blood and nutrients to the muscles.
4. The body becomes slightly more acidic as the kidneys age. Acidic environments trigger protein breakdown.
HOW MUCH PROTEIN DO YOU NEED?
Compelling research indicates that with age your ability to utilize protein to support and synthesize muscle may be blunted. Consequently, the adequacy of the recommended dietary allowance (RDA) for protein of 0.8 grams per kilogram per day (g/kg/d) for older people has come into question. But no scientific consensus has been reached.
A new position paper on the nutritional needs for older adults (age 60 and older) published in the August 2012 Journal of the Academy of Nutrition and Dietetics suggests a range of protein intake between 1 to 1.6 g/kg/d. Fielding advises 1 to 1.2 g/kg/d for people over 60 to maintain and build muscle mass, as well as to ensure adequate intake of the essential amino acid leucine.
Fielding explains, "Leucine has a potent effect on stimulating muscle protein synthesis. If you consume protein foods that are rich in leucine, they seem to stimulate muscle protein synthesis more than other comparable protein foods." Sources of leucine include milk, whey, tuna, beef, chicken, soy, peanuts, and eggs.
For a man weighing about 154 pounds, 1 to 1.2 g/kg/d of protein equates to 70 to 84 g, compared to 56 g recommended at the current RDA level. With this kind of increase in protein, should you be concerned about kidney health? In the absence of kidney disease, Fielding reports no safety concerns. He adds, "The effects of protein intake on renal function are largely overstated."
The Academy of Nutrition and Dietetics position paper suggests an intake of about 25 to 30 g of protein at each meal for older adults. You can achieve this intake level by including protein-rich foods, such as lean meat, poultry, fish and seafood, eggs, dairy products, beans, lentils, soy foods, nuts, and seeds at each meal. In addition, servings of whole grains and vegetables can also help you meet your protein goals.
THE BOTTOM LINE
There are no approved medications at this time to manage or prevent sarcopenia, although researchers are attempting to identify safe and effective treatments. In the meantime, balanced diets with adequate protein and strength training are the best and only tools we have to combat muscle mass and strength losses.