Q: What exercise will help me stay trim as I get older?

A: Successful weight loss is never easy, and becomes more difficult with age. Most of us gain a pound or two each year during middle age. We also often begin naturally to lose some of our muscle mass.

This change in body composition matters, because as the percentage of our body composed of fat tissue rises, our metabolic rates fall and we burn fewer calories. We also become less strong as our muscles shrink.

So most experts agree that the ideal weight-loss program would maximize fat loss while sparing muscle mass. But this is difficult to achieve: Typically, when we drop a pound, as much as a third of that loss can come from muscle, with the rest composed of fat.

Training with weights could be more effective than a walking program, according to a new study in Obesity by researchers at Wake Forest University.

Study participants who had cut calories but not worked out lost an average of about 12 pounds. Those who had cut calories and walked dropped about 20 pounds, while those who had dieted and weight-trained also lost about 20 pounds. But body-composition scans showed that the weight trainers had lost about 2 pounds of muscle and 18 pounds of fat, while the walkers had dropped about 4 pounds of muscle and 16 pounds of fat.

“Walking is excellent exercise,” said Kristen M. Beavers, an assistant professor of health and exercise science and the study’s lead author. But it might not prompt older people’s bodies to hold on to muscle as effectively as weight training, she said.

— Gretchen Reynolds, The New York Times