Some weight regain is common after weight loss, but in older women many of those regained pounds return as fat mass rather than muscle mass, according to a new study.
How this affects strength and health needs further study, but experts said the findings underscore the downside of so-called yo-yo dieting.
The study included 78 women, average age 58, who had lost about 25 pounds during a previous diet study. Looking at data on the regainers, the researchers found a change in body composition.
"A third of the weight lost was muscle," said Dr. Barbara Nicklas, a gerontologist at the J. Paul Sticht Center on Aging and Rehabilitation at Wake Forest Baptist Medical Center in Winston-Salem, N.C.
"The proportion of weight they gained 1/8back3/8 as muscle was 20 percent." That left them with more fat and less muscle.
The researchers evaluated the women's body weight, lean mass and fat mass before the diet, right after weight loss, and six and 12 months later. At one year, the researchers zeroed in on 68 women for whom complete records were available. Fifty-two (76 percent) had regained some weight, including 11 who weighed more than at the study's start. Sixteen were still losing weight.
The study was published Dec. 13 in the American Journal of Clinical Nutrition.
The women in the study were sedentary, and their average body mass index (BMI) at the start was 33. BMI is a calculation based on height and weight, and a BMI of 30 is considered obese.
The finding may not apply to women who are less overweight, Nicklas said. She suspects the results would also apply to older men, but perhaps not to younger men or women.
"Some research shows (younger people) regain their weight in the same muscle-fat proportion they lost (it)," she said.
There is a possibility, Nicklas said, that a higher proportion of fat with the regained weight may simply reflect normal aging.
The study of regain after weight loss is a relatively new area, said Dr. Alice Lichtenstein, a professor of nutrition science at Tufts University, Boston, who is familiar with the study.
"There was a wide range of variability in both weight loss and regain among the postmenopausal women studied," she said. The shift in body composition toward more fat than muscle didn't occur in all women, she said.
Even so, she said the clear message is to try to avoid becoming overweight to begin with, and to keep off the excess weight once you lose it.
"For those women who have gained excess body weight and are then successful in losing it, this finding may add a bit more impetus to maintain the weight loss," Lichtenstein said.
But the study shouldn't deter overweight individuals from trying to slim down, she said.
Protein consumption is important to help minimize the amount of muscle loss, Nicklas said.
U.S. dietary guidelines recommend 0.8 grams of protein (or more) for every 2.2 pounds of body weight. For instance, a woman who weighs 200 pounds should take in about 70 to 90 grams of protein, Nicklas said. A 5.3-ounce container of Greek yogurt has about 13 grams or more of protein, she noted.
Exercise and a balanced diet can help maintain weight loss, Nicklas advised.