"OK, team! After age 40 we can start losing muscle—8 percent every 10 years," warns an animated bottle of the nutritional drink Ensure Muscle Health in a TV ad. "But you can help fight muscle loss with exercise and Ensure Muscle Health," the bottle shouts as it pumps resistance bands in a refrigerator.
The drink, part of the Ensure line of nutrition shakes, contains a trademarked amino-acid metabolite called Revigor. The manufacturer claims in its ad that Revigor can "help rebuild muscle and strength naturally lost over time" when added to exercise. There's no question that regular strength training can slow muscle loss and build new muscle. But more research is needed to prove whether adding Ensure Muscle Health provides an additional benefit. Revigor is a source of hydroxymethylbutyrate (HMB), a byproduct created when the body metabolizes the amino acid leucine. Some small, short-term studies have suggested that supplements of HMB might help adults gain more lean muscle mass from strength training, particularly if they're not fit to begin with. But overall, the results of the studies are conflicting.
In addition, our experts point out, most people need fewer calorie-dense foods in their diets, not more. An 8-ounce bottle of Ensure Muscle Health contains 250 calories. To get the 3 grams of HMB tested in the studies, you'd need to drink two bottles, or 500 calories' worth. (The label recommends drinking two bottles a day.)
Bottom line. The benefits of strength training are well established, but research on HMB is still preliminary. And getting the ingredient through a high-calorie shake could lead to weight gain if you don't account for the extra calories in your diet.