Glucagon-like peptide-1 receptor agonists, a class of peptides that mimic a gut hormone involved in appetite and blood-sugar regulation, have become widely studied tools for obesity research. The weight loss they produce in clinical trials is substantial. But a growing body of evidence raises a specific concern: a large share of the weight that disappears during treatment may not be fat. According to a recent abstract published in JCI Insight, as much as 45 percent of the total weight lost with one of these peptides could come from skeletal muscle rather than stored body fat.
Skeletal muscle is not just a cosmetic concern. It drives everyday movement, supports metabolic health, and helps the body regulate blood sugar. Losing a meaningful portion of it during a weight-loss intervention could create problems that outlast the treatment itself. Researchers set out to ask a straightforward question: could adding an oral ketone ester supplement to the regimen prevent that muscle loss, and if so, how?
The study used obese, glucose-intolerant mice as a model and ran for three weeks, tracking body composition, muscle strength, and endurance alongside detailed molecular measurements. The results, the researchers argue, point to a specific biological mechanism and suggest a potential strategy worth testing in humans.
The muscle-loss problem with GLP-1 receptor agonists
GLP-1 receptor agonists work largely by reducing appetite, slowing how quickly the stomach empties, and improving the body's response to insulin. In obese animal models and in human trials, they reliably reduce total body weight. The complication is that the body does not shed weight selectively. When calorie intake drops sharply, the body draws on multiple tissue stores, and muscle is vulnerable.
The abstract notes that semaglutide, a well-studied GLP-1 receptor agonist, reduced lean mass in mice and impaired both muscle strength and endurance. At the molecular level, the researchers found suppressed expression of genes associated with mitochondrial function inside muscle tissue and elevated expression of genes linked to muscle atrophy, the cellular process by which muscle fibers break down. This combination, impaired energy production at the cellular level alongside an active breakdown signal, gives researchers a working hypothesis about why the muscle loss occurs.
What ketone esters are and why researchers tried them
Ketone bodies are small molecules the liver produces when carbohydrate availability is low, such as during fasting or prolonged exercise. The best-studied ketone body is beta-hydroxybutyrate, often abbreviated BHB. In normal metabolism, muscle tissue can use BHB as a direct fuel source, and some research suggests it also carries signaling properties that influence gene expression related to muscle maintenance.
Ketone esters are synthetic compounds that, when consumed orally, are broken down in the gut to release BHB quickly and predictably. Because they raise blood ketone levels without requiring fasting or strict dietary change, researchers have used them as a controlled tool to study ketone biology in isolation. The JCI Insight study used a BHB-generating ketone ester added to the diet of the same obese mouse model already receiving the GLP-1 receptor agonist.
The logic behind testing this combination is that if mitochondrial defects and impaired ketone metabolism are contributing to muscle breakdown during GLP-1 treatment, then supplying an exogenous ketone source might restore the missing fuel signal and interrupt the atrophy pathway.
What the mouse study measured
Three groups of obese, glucose-intolerant mice were compared over three weeks. One group received a vehicle control, one received the GLP-1 receptor agonist alone, and one received the GLP-1 receptor agonist together with the ketone ester supplement. Body composition was tracked over time, along with functional measures of muscle strength and endurance.
The researchers also analyzed gene expression in skeletal muscle tissue at the end of the study, looking specifically at markers of mitochondrial activity and markers of muscle atrophy pathways. This molecular layer is important because it connects the physical changes in body composition to a plausible mechanism rather than leaving the observation at the level of weight alone.
Key findings from the combination group
In the group that received both the GLP-1 receptor agonist and the ketone ester, skeletal muscle mass was preserved relative to the group that received the GLP-1 receptor agonist alone. Muscle strength and endurance measurements also remained closer to baseline in the combination group. Critically, the fat loss associated with the GLP-1 receptor agonist was not diminished. The ketone ester appeared to protect muscle selectively, without blunting the metabolic effect the researchers were trying to preserve.
At the gene-expression level, the combination treatment prevented the changes seen with the GLP-1 receptor agonist alone. Mitochondrial gene expression was maintained closer to normal levels, and the upregulation of atrophy-related genes was attenuated. The researchers interpret this as evidence that the ketone ester was acting on the specific molecular pathways disrupted by the GLP-1 receptor agonist, rather than simply adding calories or changing energy balance in a nonspecific way.
Proposed mechanism
The abstract points to two interrelated processes as likely contributors to GLP-1-induced muscle loss. First, mitochondrial dysfunction within muscle fibers reduces the cell's capacity to produce energy efficiently. Second, when the muscle cannot adequately metabolize ketone bodies, it may lose a key protective signal that normally suppresses atrophy pathways.
By supplying BHB through the ketone ester, the researchers hypothesize that the muscle receives the metabolic substrate it needs to maintain mitochondrial function and, as a downstream consequence, resists the atrophy signals that the GLP-1 receptor agonist appears to amplify. This is still a mechanistic hypothesis grounded in mouse data, and the authors are careful to call these preclinical findings that require human evaluation before any clinical conclusions can be drawn.
Limitations and the road to clinical evidence
Mouse models of obesity are useful for establishing biological plausibility and identifying mechanisms, but they do not map directly onto human physiology. Obese, glucose-intolerant mice differ from diverse human populations in drug metabolism, hormonal environment, and baseline muscle composition. The three-week timeline is also short relative to the months or years over which these treatments are typically studied in humans.
The authors explicitly call for clinical evaluation to assess whether the findings translate. Until controlled human trials are completed, the literature suggests only that the hypothesis is mechanistically coherent and that the preclinical evidence is promising. Early data points at ketone supplementation as a candidate strategy, not a confirmed intervention. Researchers in this area will likely focus next on dose-finding in humans, safety monitoring for the combined regimen, and longer-term body-composition outcomes.
