By Barbara Berkeley
The common wisdom tells you to build it. Most people think they don’t have enough of it. Fitness experts tout it as something almost magical. But what’s the real deal with muscle?
I have the strange habit of reading certain research papers repeatedly. The tendency to read things over and over may be inherited. My father loves to read certain books dozen of times. We have a copy of “Shogun” at my house that is literally falling apart; ditto “Prizzi’s Honor,” “Lonesome Dove,” and “The Godfather.” But research papers? I can only say that there are just some articles that I enjoy as much as a novel! When I found myself re-reading (for the umpteenth time) my favorite paper on muscle, it occurred to me that perhaps I should share the love.
My dog-eared, underlined, thinning favorite paper is called “The Underappreciated Role of Muscle in Health and Disease.” It was published in the American Journal of Clinical Nutrition in 2006 and is one of the only reviews I’ve ever read that focuses on exactly what muscle does. We talk an awful lot about muscle, but its real importance – the vital role that muscle plays – is virtually never discussed. For those of you who would like to slog through the scientific jargon, I’ve provided a link to the paper. If you’d prefer the CliffsNotes version, read on.
The story of muscle starts and ends with protein. Proteins, made up of various amino acids, are the materials that build our organs and repair the damage we incur every day just from living. We cannot survive without a steady supply of proteins because this daily wear and tear causes unavoidable organ breakdown. Proteins repair this damage. Think of yourself as a building that is exposed to the environment 24/7. As your paint starts to wear away and your façade starts to weather, there are workmen who are constantly repairing the damage. They are fixing you up with buckets of protein.
Eating foods with proteins provides a flood of amino acids to your body. These are reassembled into new combinations to form the exact proteins needed for that day’s repair. The need for amino acids is a 24 hour-a-day situation. So here’s a question: Where do amino acids come from if you’re not eating or if you are asleep? The answer is: from muscle. Muscle is a bank. Your body withdraws protein from muscle to accomplish repairs. When you eat, most of the protein you ingest actually goes to replace what’s been “borrowed” from your muscle in the hours before.
People who are obese actually have larger stores of muscle than lean people. Studies have shown that these big banks of muscle can keep protein levels normal after as many as 60 days of fasting! On the flip side, when muscle shrinks to about half of its normal amount, life can no longer be supported. Observation of people who have undergone starvation conditions has shown that it is the critical loss of muscle mass that leads to death. Once there is no longer enough protein in the bank, repair ceases and so does life.
Muscles are even more important protein “lenders” when we suffer from conditions that greatly accelerate the body’s need for protein. Injuries, illnesses, operations, burns, cancer, chemo, and other physical stresses greatly increase demands for repair proteins. Sometimes, a seriously ill person can have protein needs that can be as much as four times those of a healthy person. These can’t be met through diet alone, so the muscle bank is accessed for massive withdrawals. Those who start out with a large amount of muscle mass will have a greater likelihood of getting through such an event.
Since our muscular bank account is so vital, we need to worry about that fact that we can lose muscle as a consequence of aging. Loss of muscle is called “sarcopenia” (sarco=muscle, penia=impoverished) and it is a common problem for older people. Sarcopenia is estimated to occur in about 30% of those over 60. Sarcopenic people are frail, tend to have more falls, and have more difficulty with daily activities. As we saw above, decreased muscle mass not only means weakness, but an inability to fight off serious illness.
What about the much touted ability of muscle tissue to burn calories? Muscle burns calories when it remodels itself by either adding to or breaking down its mass. These processes take energy and, as we’ve discussed, are constantly occurring because of the withdrawal and redeposit of protein which is normal operating procedure. However, larger muscle masses have higher rates of turnover and calorie burn than smaller masses. A young man, for example, might have about 80 pounds of muscle which burns 485 calories per day. An elderly woman is likely to have just 30 pounds of muscle, providing only 120 calories of burn. This calorie burn is independent of exercise, by the way. It is part of the “resting metabolism”; calories which are burned when we simply sit still. You can see that the metabolic difference between the young man and the older woman is quite large. Now you know why your 17-year-old son can eat seemingly endless amounts of food without weight gain. You can also understand why building extra muscle might help you to maintain weight loss. Even at rest, the extra muscles and their turn over will burn extra calories for you. The problem is that building extra muscle is not all that easy, especially if you are a woman or are older.
When people become obese, they do not gain fat alone. They also gain muscle which supports the heavy fat tissue. This can potentially be used to the overweight person’s advantage. Theoretically, if this extra muscle can be preserved during weight loss, the calories it burns will make weight maintenance more likely. We also know that we can increase the rate of muscle turnover by providing a stream of amino acids in the diet. These amino acids start the muscles to work, but the fuel the muscle uses to build and rebuild itself actually comes from FAT. In fact, fat is “the preferred energy substrate of resting muscle.”
Thus, we have the rationale for recommending higher protein diets for weight loss. Theoretically, the hefty amount of amino acids gets that big muscle mass turning over. Turn-over then contributes to fat burning. In addition, dietary protein keeps muscle mass from disintegrating as weight is lost. The idea is to get fat to burn preferentially while leaving the dieter with a hefty amount of calorie-burning muscle. In our clinic, we use high-protein liquid drinks and one dinner meal to get weight loss. We find that the combination works very well, perhaps for this reason. We might also extrapolate that continuing to eat diets that focus on goodly amounts of protein will stimulate muscle to maintain itself, turn over actively, and burn fat calories in the process.
Muscle also plays a pivotal role in insulin resistance, which can lead to diabetes. Normally, insulin tells the muscles to accept sugar from the blood. This is one of the ways that insulin keeps blood sugar controlled. As weight gain progresses, many people develop insulin resistance; an inability of the muscle to take up sugar when insulin calls. The body compensates by making too much insulin which in turn leads to high blood pressure, cholesterol and triglyceride problems and eventually, high sugar in the blood.
The question is, why should muscles become resistant to insulin?
While we’re still not sure, this paper notes that people with insulin resistance have muscles which have become filled with fatty globules, visible on MRI. This inappropriate fat storage seems to be linked to insulin resistance and may reflect a problem with the muscle mitochondria, small cellular engines which normally burn fat. Instead of fat being burned, it is being deposited within the muscle. Physical activity seems to tell the mitochondria to work properly. “…As little as a single bout of exercise…can transiently reverse insulin resistance,” the paper reports. This is crucial information for those of you who either have or have experienced insulin resistance. Keep exercising to keep your mitochondria burning fat rather than storing it. This will lessen resistance problems.
What about ways to preserve or build the muscle mass you have? Once you become sarcopenic , it is very hard to reverse the loss. Efforts should focus on preserving the mass you have as a young- or middle-aged person. Remember that the goal of exercise should not be simply to grow big muscles. The effect that exercise has on getting the muscles to work efficiently at a cellular level is just as important even though it can’t be seen with the naked eye.
The bottom line? No one seems to have exact recommendations for protein intakes. Don’t be afraid to add some low-calorie protein shakes or bars to your regimen if you are trying to build and maintain muscle. Make sure that you are getting adequate protein, particularly if you are vegetarian and most specifically if you are vegan. Keep up your exercise, not only to preserve the muscle you have, but to assure that it works properly. Keep exercising throughout your life in order to minimize your chances of sarcopenia as you age. Maintain muscle at good levels in order to give yourself the best chance of weathering unintended storms like illness or injury.
Like most of our body parts, muscle is not as simple as it seems. We will benefit greatly by feeding it, building it and taking care of it. If I fall in love with any other research papers anytime soon, I’ll be sure to share them.
