Some patients find that medication-induced weight loss lessens rather than improves fitness, because another side effect is muscle loss. Several trials have reported that 35% to 45% of GLP-1 weight loss is not fat, but “lean mass” including muscle and bone.
Bill Colbert’s cherished hobby for 50 years, reenacting medieval combat, involves “putting on 90 pounds of steel-plate armor and fighting with broadswords.” A retired computer systems analyst in Churchill, Pennsylvania, he started on Mounjaro, successfully lowered his blood glucose, and lost 18 pounds in two months.
But “you could almost see the muscles melting away,” he recalled. Feeling too weak to fight well at age 78, he also discontinued the drug and now relies on other diabetes medications.
“During the aging process, we begin to lose muscle,” typically half a percent to 1% of muscle weight per year, said Zhenqi Liu, an endocrinologist at the University of Virginia who studies the effects of weight loss drugs. “For people on these medications, the process is much more accelerated.”
Losing muscle can lead to frailty, falls, and fractures, so doctors advise GLP-1 users to exercise, including strength training, and to eat enough protein.
Patients 65 and older were 20% to 30% more likely than younger ones to discontinue the drugs and less likely to return to them.
What explains this pattern? As many as 20% of patients may experience gastrointestinal problems. “Nausea, sometimes vomiting, bloating, diarrhea,” Anderson said, ticking off the most common side effects.
