Ketone supplementation preserved muscle and its energy-producing machinery during weight loss induced by a GLP-1 drug in mice. Digest
Weight loss can look successful on the scale while concealing whether the body lost fat or muscle. Researchers tested whether raising ketone levels during treatment with semaglutide, the weight-loss drug sold under brand names such as Ozempic and Wegovy, could protect skeletal muscle without interfering with fat loss.
Male mice with diet-induced obesity and poor blood sugar control entered a three-week rapid-weight-loss experiment as they switched from a high-fat diet to regular food under calorie-deficit conditions. They were randomly assigned to inactive saline control injections, semaglutide, or semaglutide plus a ketone ester that raised blood ketones to levels that can occur naturally during fasting.
- The ketone ester preserved lean tissue during semaglutide-driven weight loss while allowing the same fat loss. As a result, the group receiving the combined treatment lost less weight overall but potentially retained more total muscle mass.
- Skeletal muscle weighed more and muscle fibers were larger with ketone cotreatment than with semaglutide alone.
- The ketone ester also protected grip strength and improved exercise endurance.
- Differences in total calorie intake did not explain muscle preservation. At the times when muscle loss was greatest, semaglutide-only mice consumed more total calories than the combination group.
Muscle requires a steady supply of usable energy to maintain and rebuild its proteins. During rapid weight loss, ketones can serve as an alternative fuel when energy from food is limited. In the semaglutide-only group, levels of several components of the cellular machinery for processing ketones and generating energy fell, while several gene signals tied to muscle protein breakdown rose. The ketone ester preserved these molecular patterns. Keeping ketone fuel available may therefore help muscle meet its energy needs and avoid shifting toward tissue breakdown. However, this remains a mechanistic interpretation rather than proof of the precise pathway.
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Taken together, ketone cotreatment allowed semaglutide-treated mice to lose fat while retaining more muscle mass, strength, and endurance. The divergence suggests that the composition of rapid weight loss may depend on whether muscle can preserve the flexibility to switch toward alternative fuels when energy intake falls.