Fri: Time to Take Back Wisconsin

There's No Such Thing as a Free Light Lunch.

The newest and much-hyped obesity drugs are, at their core, powerful appetite suppressants. When you eat fewer calories than you burn, the body starts scavenging itself, breaking down fat, of course, but also muscle. About a quarter to a third of the weight shed is lean body mass, and most of that is muscle.

Muscle loss is not inherently bad. As people lose fat, they need less muscle to support the weight of their body. And the muscle that goes first tends to be low quality and streaked with fat. Doctors grow concerned when people start to feel weak in everyday life—while picking up the grandkids, for example, or shoveling the driveway. Taken further, the progressive loss of muscle can make patients, especially elderly ones who already have less muscle to spare, frail and vulnerable to falls. People trying to slim down from an already healthy weight, who have less fat to spare, may also be prone to losing muscle. “You have to pull calories from somewhere,” says Robert Kushner, an obesity-medicine doctor at Northwestern University, who was also an investigator in a key trial for one of these drugs.

Kushner worries about patients who start with low muscle mass and go on to become super responders to the drugs, losing significantly more than the average 15 to 20 percent of their body weight. The more these patients lose, the more likely their body is breaking down muscle. “I watch them very carefully,” he told me. The impacts of losing muscle may go beyond losing just strength. Muscle cells are major consumers of energy; they influence insulin sensitivity and absorb some 80 percent of the glucose flooding into blood after a meal. Extreme loss might alter these metabolic functions of muscle too.