What do muscle mass and strength have to do with how well we age?
After 30, your muscle mass dwindles some 3-8 percent each decade. Once you hit 60, these losses accelerate even more quickly. The consequences are far more serious than a change in your appearance. Declining muscle mass doesn't simply mean your shoulders are less toned or that you can't achieve the same results in sports that you did as a teenager. These muscle changes have implications that are much bigger than your new pant size. The effects are serious and far-reaching. They determine how healthy and active you'll remain for the rest of your life.
Decreased muscle mass means you'll burn far fewer calories. If you take in the same amount that you did when you were younger, you'll start accumulating body fat. Your muscles require a lot of calories to maintain: Think of them as a bunch of high-strung, active family members visiting your home. They're always up, moving around. As a result, they're hungry and require a lot of food.
Imagine that these demanding visitors gradually leave, one by one, and the remaining folks start lying on the couch. This is like your muscles becoming smaller and weaker. These relaxed visitors don't need as much food, but you keep buying the same amount of groceries that you bought when you had a big group of active guests. This is like eating the same amount of calories you did when you had more muscle. Gradually, your cupboards and refrigerator overflow with unused food. This is like storing up fat from those unnecessary calories.
Even if your body weight stays the same, less of your weight is from muscle and more is from fat. That's because calories are stored (as fat) when there is less muscle to burn them. More fat equals less calorie-burning muscle. Internally, the extra fat increases your risk of diabetes, stroke and some cancers. Externally, your body shape changes as muscle morphs to fat. This means bigger jeans and fewer fitted tops.
Also, the strength of your muscles is related to the strength of your bones. Women are likely more focused on keeping their bones dense and strong than on maintaining their muscles, because the medical establishment, society and the media have put more focus on preventing osteoporosis. However, when your muscles are weak, your bones are more likely to be weak. Exercise that helps your muscles helps your bones, too.
Declining muscle mass and strength also mean you'll be less likely to get around in your later years. Being able to move freely is a crucial component of healthy aging. Whether it's continuing your workout schedule at the gym, carrying groceries, cleaning your home, getting in and out of a chair or stepping in and out of your shower, your ability to do these activities helps determine your independence.
Finally, shrinking muscles may grow less responsive to insulin. Your muscles are avid consumers of glucose, or blood sugar, but they need to use the hormone insulin so the blood sugar can enter their cells. When they become insulin resistant, the sugar can't enter. This puts you at greater risk for Type 2 diabetes, which in turn raises your risk of heart disease, stroke and, perhaps, Alzheimer's.
So, maintaining your muscles isn't just an exercise in vanity. It's about staying fit, vital, independent and free of disease. Best of all, you have a lot of control over your muscle mass and strength -- more than you realize. Experts have seen that declining muscle isn't just an unpreventable fact of aging. In large part it's due to lack of use. Still, even people in their 90s can show impressive strength gains with exercise. Most women -- whether young, boomers or seniors -- are in a prime position to prevent the serious consequences of muscle loss.
As you age, a number of changes occur in your skeletal muscles, which are the ones that move your arms, your legs and the rest of your body. You lose muscle mass -- you simply have less of the stuff. Your nervous system becomes less efficient at prompting your muscles to move. Fat and connective tissue start developing within your muscles, leaving less muscle tissue to contract to move your body.
However, it's worth repeating: Although hormonal processes cause some muscle changes over the course of your life, shrinking muscle mass and decreasing strength aren't caused by age alone. Here are some of the factors that contribute to declining muscles as you venture into your later years.
Lack of use. Your body is designed to move and lack of movement is a significant factor in muscle decline. Studies have shown that even young people's muscle mass and strength quickly deteriorate when they're confined to bed rest. And research has found that older men and women who are less active have less muscle mass and more disability. Conversely, training programs of just a few months in duration have been shown to significantly increase older people's strength. Even frail people who've already passed their 90th birthday can add muscle mass and strength. And if you can improve your muscles' capability deep into your 90s, there's no excuse for slacking off now whether you're 30-, 50- or 70-something!
Insufficient protein. The current RDA (Recommended Daily Allowance) for protein -- the amount that people are supposed to get each day -- is 0.8 grams per kilogram of body weight for adults. So if you weigh 130 pounds (59 kilograms), you need 47 grams of protein daily. I recommend that 30 percent of your daily calories come from lean protein (with 45 percent from complex carbs and 25 percent from good fats). This is a little higher than the RDA, but you will be exercising and building muscle as a part of the "Biggest Loser" plan.
Experts are discovering that many older people aren't getting enough protein in their diets and that the 0.8 grams per kilogram recommendation may not be enough in the first place. Whether or not your goal is weight loss, if you're trying to build muscle (and burn fat), it's crucial that your protein needs are being met. Individual protein recommendations vary per person, depending on weight and body composition. If you have any health conditions, such as kidney disease, that may affect your protein requirements, consult with your medical provider to determine your personal protein requirement.
Hormonal changes. Women -- if you're on hormone replacement therapy (HRT), you've probably learned firsthand that extra estrogen can cause a weight gain in fat, not muscle. Discuss the estrogen and progesterone balance of your HRT with your doctor and be sure to stay on top of your exercise routine, even if that means consulting a personal trainer to get you started.
Next week I'll continue with ways to measure (and build!) your muscle.
Cheryl Forberg RD is a James Beard award-winning chef, Nutritionist for NBC's The Biggest Loser and NYT bestselling author. Her latest book is Flavor First (Rodale). She lives on a farm in Napa, California. For more nutrition and cooking tips, visit Cheryl's website