DENVER — In addition to the established gastrointestinal side effects common with the highly effective anti-obesity drugs, there is growing discussion around their potential to contribute to the loss of lean mass, necessary to keep the metabolic engine running full-steam.
And although measures should be recommended to prevent those effects, experts also want to remind clinicians that the loss of lean mass is indeed expected with most weight loss interventions — when they’re successful.
“The bottom line is if you’re successful with weight loss, it’s a normal process that you’re going to lose some lean mass,” Angela Fitch, MD, associate director of the Massachusetts General Hospital Weight Center in Boston, said during a presentation on the issue at Obesity Medicine 2024.
“It’s what we would expect to see if you successfully lost weight with bariatric surgery or with an intense lifestyle intervention,” said Dr. Fitch, past president of the Obesity Medicine Association.
“The difference is, there haven’t been nearly as many people being successful with weight loss with those other interventions,” she noted. “But with the popularity of the glucagon-like peptide 1 (GLP-1) medications, people are hearing this for the first time and saying, ‘Oh my gosh, 30% of the weight loss is muscle mass — that’s horrible.’ “
, which have been reported in clinical trials of the GLP-1s semaglutide and the dual glucose-dependent insulinotropic polypeptide tirzepatide to range from about 25% to 40%, respectively, of weight loss.
“Excess adiposity is what makes us sick — not our weight,” Dr. Fitch underscored. “The amount of fat that people are losing [with anti-obesity medications] is far more beneficial than maybe the potential that they’ve lost a little bit of lean mass,” she said.
She cited research suggesting that significant weight loss from bariatric surgery is linked to increases in life expectancy, cardiovascular risk reduction, cancer risk reduction, and a wide array of other positive effects — despite the loss of lean mass that occurs with the weight loss.
Opportunity for Awareness
The increased attention on issues of body composition accompanying weight loss importantly provides clinicians the chance to underscore to patients the importance of offsetting the loss of lean mass through strength training, nutritional choices, and other measures.
However, patients should be prepared that achieving these goals can be more challenging than expected, said Dr. Fitch.
“It can be very hard to be in an energy deficit (due to a weight loss regimen) and gain muscle mass,” she said. “When athletes are trying to gain muscle mass, they’re increasing their intake to do so. It doesn’t come naturally in today’s world.”
Nevertheless, patients can be reassured that the losses can be reversed with some effort, Dr. Fitch noted.
She cautioned that for those who succeed in building or rebuilding lean mass, the evidence may be reflected on the scale, with numbers going up, not down — something they may not wish to see.
“Patients tend to freak out when they see the scale going up after losing all of that weight, but you can reassure them that it’s okay — this is healthier weight gain.”