Weight loss results in more than just a loss of fat, it causes loss of muscle as well. Because of this, dieting without exercise is not typically recommended for older adults, as muscle loss can lead to frailty and a decline in physical function. However, recent research determined that overweight, postmenopausal women who embarked on controlled weight-loss programs did not suffer adverse physical affects.
The conclusion was made as the result of two projects from Wake Forest University Baptist Medical Center, Winston-Salem, NC, both of which are part of the larger Diet, Exercise and Metabolism in Older Women (DEMO) study.
One study evaluated 23 obese, postmenopausal, sedentary women with a mean age of 58 who participated in the DEMO study. For five months, their meals and snacks were provided by the study and contained 400 fewer calories than they needed to maintain their weight. Participants' body composition and physical function were measured before and after the five-month period. Tests of physical function measured knee strength, hand-grip strength, walking speed, aerobic fitness and ability to quickly rise from a chair without using their arms. The women lost an average of 25 pounds, with muscle representing about 35% of the total loss.
“Despite the large amount of muscle loss, their aerobic fitness and their ability to rise from a chair showed a trend toward improvement,” says Dr. Jamehl Demons, lead investigator on the project evaluating the effects of weight loss on physical performance. “Their strength and walking speed did not change. This suggests that their weight loss through dieting wouldn't be expected to lead to increased disability.”
But losing weight is only part of the equation. Most people who successfully lose weight tend to regain most or all of it, and little is known about whether the regained weight is fat or muscle. In older adults, regaining a significant amount of fat could be risky because of the potential to end up with less muscle than when they started.
The second study evaluated 30 women from the DEMO study to determine body composition when weight was regained. Body composition was measured before and after the five-month period of calorie restriction. A third measurement was taken 12 months later. The women lost an average of 25 pounds; about 32% of the lost weight was muscle; 68% was fat. The women regained an average of 11 lbs. About 27% of the regained weight was muscle; 73% was fat.
“Weight regain in the year following an intensive weight-loss program is accompanied by gain of both fat and lean mass, with relatively more fat gain and less lean gain,” says Mary F. Lyles, lead investigator on an analysis exploring how dieting affected body composition. “It looks like they are better off than if they had never tried to lose weight.”
