GLP-1 medicines: keeping muscle, and keeping the weight off

GLP-1 medicines have changed weight loss for a lot of people. They reduce appetite and make it possible to feel satisfied on much less food. In the main semaglutide trial, people lost about 15% of their body weight over 68 weeks, and for many it was the first time eating less had ever felt manageable.[1]

This guide is about the two things the prescription doesn't do for you. Your prescriber stays in charge of the medicine itself: this isn't advice about starting, changing or stopping it.

One: some of what you lose is not fat

When you lose weight, some of the loss is lean mass. Lean mass is everything that isn't fat or bone: muscle, but also water, organs and other tissue. In a body-composition study inside the semaglutide trial, fat mass fell by about 19% and lean mass by about 10%, so roughly two fifths of the weight lost was lean mass rather than fat.[2]

Two things are worth saying about that number, because it often gets repeated as "39% of the weight you lose is muscle".

• Lean mass is not the same as muscle. A body scan measures lean mass, not muscle alone, so part of that loss is water and other tissue.
• Some lean mass loss happens with any large weight loss, with or without a medicine. In that same study, people ended up with a higher proportion of lean mass than they started with, because they lost so much more fat.[2]

Still, losing strength while you lose weight is worth avoiding. Muscle is what lets you carry shopping, climb stairs and train hard, and it supports blood sugar control. Its effect on how many calories you burn at rest is smaller than the internet suggests, so the honest reason to protect it is capability, not metabolism.

Two: the medicine doesn't teach you anything

GLP-1 medicines quiet appetite. They don't change what you know about feeding yourself or training. In the follow-up to that trial, people who came off the medicine regained about two thirds of the weight they had lost within a year.[3] That isn't weakness, it's what happens when the only thing that changed was the prescription.

The window while your appetite is quiet is the best time you will ever get to practise the habits that hold the result: a way of eating you can repeat, and training you actually do.

While you're on it: protect your strength

• Lift weights two or three times a week. Resistance training plus enough protein is the best-supported way to limit muscle loss while losing weight. Full-body sessions are enough. My free 3-day full-body programme is built for this.
• Aim at the higher end of 1.6 to 2.2g of protein per kg of body weight a day. Across the research, extra protein stops adding much benefit at about 1.6g per kg, with the upper end of the useful range around 2.2g.[4] On a GLP-1, hitting it is the hard part, so eat the protein part of your meal first, lean on dairy and eggs, and don't be precious about shakes on low-appetite days. The protein guide has practical numbers.
• Eat enough. The common problem on these medicines is not overeating, it's under-eating for weeks. If you're losing more than about 1% of your body weight a week, or you can't get near your protein target, tell your prescriber and your coach.
• Keep your daily steps up. It's the easiest habit to keep when energy is low, and it protects how much you move day to day.

Coming off: plan it, don't endure it

If you and your prescriber decide to stop, the transition is where the result is won or lost. This is coaching advice, not a medical rule.

• Start four to six weeks before you stop. Practise the eating pattern and the training while appetite is still quiet, so the habits are in place before hunger returns.
• Expect appetite to come back. It's physiology, not failure. Decide in advance what you'll do: protein-anchored meals, a consistent eating window and a short list of filling foods for hungry days.
• Find your maintenance calories. Hold your weight steady for a few weeks and you have your number. Most people can stop logging once the pattern is automatic.
• Watch the trend, not the day. Weigh yourself first thing, judge the weekly average, and agree with yourself in advance what happens if the trend climbs. It's a two-week correction, not a crisis.

Where coaching fits

None of this is complicated, but most of it is easier with someone watching the trend with you: adjusting training as your weight changes, checking the protein maths, and saying "this is normal, hold the line" in the week the appetite comes back. If you're on a GLP-1 medicine, or planning to come off one, you're welcome here, and your prescriber stays in charge of the medicine.

References

1. Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). New England Journal of Medicine 2021;384:989-1002.
2. Wilding JPH et al. Impact of semaglutide on body composition in adults with overweight or obesity: exploratory analysis of the STEP 1 study. Journal of the Endocrine Society 2021;5(Suppl 1):A16-A17. Read the study
3. Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism 2022;24:1553-1564. Read the study
4. Morton RW et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine 2018;52:376-384. Read the study