People lose body cells as they add years, and that translates into a lower metabolism rate because there aren't as many muscle cells to consume calories, contend researchers at the Human Nutrition Research Center on Aging at Tufts University in Boston.
"For a lot of people, the amount they eat doesn't go down as fast," says Dr. Ronenn Roubenoff, a Tufts scientist. The result: The elderly eat more than their bodies need, and they gain weight or they at least see their levels of body fat increase, Roubenoff says.
Various theories have existed as to why metabolism decreases in older people, Roubenoff says. Some scientists have argued that cells don't require as many calories because their energy needs change, perhaps because they get signals through the release of hormones.
But the nutrition center's latest research supports the idea that metabolism decreases because cells die, apparently when they commit "pre-programmed" suicide after reaching a certain age, Roubenoff says. Results of the study appear in a recent issue of the Journal of Gerontology.
The researchers at Tufts studied the metabolic rates and body compositions of 131 healthy men and women from 18 to 87 years of age. They compared changes in muscle mass between people of different ages, Roubenoff says.
Changes in the body's metabolism clearly begin after age 60, he says, and may even start in the 50s. But the good news, Roubenoff says, is that they're reversible.
The key is to build up muscles so they consume more calories, leading to loss of fat, he says.
"You may think, 'I'm trying to lose weight, and I don't want to gain another 20 pounds [in muscle],' " Roubenoff says. "But that may be exactly what you want to do."
Weight lifting is the best way to build muscles, even for the very old, he says. "It's something we've been pushing for the last six to eight years," he says. "And you don't need high-tech, fancy gyms to do it."
Bruce Craig, a professor of exercise with the Human Performance Laboratory at Ball State University, says that, as late as the 1980s, scientists were skeptical that older people could increase muscle mass by lifting weights. But research since has shown that specific types of weight-lifting programs truly can build muscle mass, he says.
The elderly should use a three-set program, in which they lift three weights one that represents 30 percent of their total strength, the next at 50 percent and the next at 70 percent, Craig says.
"You need to work at your maximum strength," he says. "Lifting a 5-pound weight 25 times won't do as good."
Even 80- and 90-year-old people can double or triple the amount of weight they can lift, Craig says.
But all senior citizens should get training in weight lifting for a week before hitting a program with gusto, he says.
"For most of the older people I've dealt with, weight lifting is extremely strange to them." Craig says. "You get a 65-year-old woman and you tell her to lift weights, she can do it, but it's strange to her."
Variation is important, he says. Exercise machines and group activities help reduce the tedium.
"The problem with most routines is that they are boring," he says. "But once you see some positive results, you've got them."
What to do:
Weight lifting is a healthy activity at virtually any age, but experts say it's especially important for senior citizens. Besides helping the body get rid of fat, weight training strengthens muscles around joints, Craig says.
Research also has shown that weight lifting helps the heart.
It's best to find someone to teach you how to lift weights. Technique is important because doing an exercise incorrectly not only can waste time, but can cause injury. But if you want to do it on your own, there are a variety of books available about weight training.
And if you're a senior citizen, remember that your goal is to increase muscle mass, not just strength.
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