Am I losing muscle on a GLP-1, and how do I stop it?

Any large energy deficit costs some lean tissue; that is not specific to these drugs. What is specific is that the mechanism works by making you want to eat less, and protein is the macronutrient people drop first when appetite falls, because it is the most filling and the least appealing when nauseated.

The result is a deficit that is large, sustained, and frequently low in protein — the exact conditions under which the body breaks down muscle.

Muscle is where most glucose is disposed of, so losing it worsens the metabolic problem the medication was meant to address. It is also the main determinant of resting metabolic rate, which means losing it makes regain easier and faster if you stop.

And it is the tissue that keeps you functional with age. Weight lost as muscle is considerably harder to put back than fat is to take off again.

Protein first, at every meal, targeted rather than hoped for — roughly 1.6 grams per kilogram of goal body weight per day is the usual working figure, which often means front-loading protein early in the day before appetite fades.

Resistance training two or three times a week is the other half, and it is not optional. Appetite suppression plus no training is the combination that produces the worst body composition outcome, even when the scale looks excellent.

Tracking body composition rather than weight alone is what makes this visible. Our nutrition work with Neil Burchill is built around exactly this problem.