Protein and muscle on a GLP-1 programme

How much muscle is lost?

Studies disagree sharply. A 2024 review of GLP-1 based therapies found some reporting lean mass loss at 40 to 60 per cent of total weight lost, and others at around 15 per cent or less.

Part of the reason is that lean mass on a scan isn't the same thing as muscle. It includes organs, bone, and the fluid in fat tissue, so when you lose fat, you lose some of the water that came with it, and the scan calls that lean mass.

So there isn't one number to give you. What matters is the direction, which is that some of what you lose will be muscle unless you make it otherwise.

Does losing muscle matter?

Yes, and not for the reason most people assume. It's not about looking toned.

Muscle is where you put glucose. It's what keeps you strong enough to do the things you want to do at seventy. And it's a big part of what you burn at rest, which is exactly what you want protected when you're trying not to regain.

Losing weight and losing muscle at the same time is how people end up lighter, weaker, and more likely to gain it back. That's the outcome worth avoiding.

How much protein do I need?

Higher than usual, because you're eating less overall and asking your body to hold on to muscle at the same time.

The figure that comes up in the review literature is 1.2 to 1.6 grams per kilogram of body weight a day, alongside resistance training. I'd treat that as a reasonable target rather than a proven prescription, because it's a recommendation from reviews rather than something a trial has tested in people on these medicines.

What matters more than hitting a precise number is that protein doesn't get squeezed out. When appetite drops, protein is usually the first thing to go, because it's the part of the meal that feels like effort.

What if my appetite is tiny?

Then you change the order, not the amount.

Eat the protein first. Fish, chicken, egg, tofu, dairy, whichever it is, before the rice and before the vegetables. If you only manage half the plate, you want the half that was doing the work.

Spread it across the day rather than trying to get it all in at dinner, because a small appetite and a big evening meal don't go together.

Best protein sources

The ones that are dense rather than bulky, and the ones you'll actually eat.

• Eggs, in any form, and cheap everywhere
• Fish and seafood, which sit lighter than red meat when you're nauseous
• Chicken and lean pork, skin off if fat is making you queasy
• Tau kwa and tempeh, and beancurd skin, which work in almost any local dish
• Greek yoghurt and milk, useful when chewing feels like too much
• Dhal, beans and edamame, though you'll need more volume for the same protein
• A protein shake or protein bars as needed for a workout, or when protein intake is lower on that day

Two things I'd avoid. Don't let a shake replace meals routinely, because you lose everything else that came with the food.

What resistance work is enough?

Less than you might think. Two sessions a week, covering the whole body, done consistently, gets you most of the way.

If a couple of hour-long sessions are hard to fit in a busy week, the same total effort split into shorter 15 to 20-minute sessions works too. Rotate through different muscle groups, and try not to work the same muscles two days running; give them at least a day to recover. What counts is the effort you build up across the week, not how it's carved up.

You don't need a barbell or a gym membership. Bodyweight work, resistance bands, and the machines at the community centre all count. What matters is that the effort goes up over time, so that the last couple of repetitions are genuinely hard.

The trap is doing only cardio because it feels like it's doing something. Walking is excellent and you should be doing it, but it won't protect your muscle. Losing weight quickly takes muscle with it. Resistance work is what tells your body to hold on.

Is there evidence for this?

There's real randomised evidence, and more of it than you'd expect.

A one year trial in 195 adults who'd already lost about 13 kilograms compared exercise alone, liraglutide alone, both together, or neither. The combination roughly doubled the fall in body fat percentage compared with either on its own.

What matters is what only the combination achieved. Improvements in blood sugar control, insulin sensitivity and cardiorespiratory fitness showed up in the exercise-plus-medication group and not in the medication-only group.

It was liraglutide rather than the newer molecules, and the programme was mostly aerobic rather than pure lifting, so it isn't a perfect match. It wasn't purely aerobic either, though. The circuit training in that programme carries a resistance element, and some strength work sits inside zone 2 intensity anyway. It's still the strongest answer available to whether training alongside treatment is worth it.

Why the scans matter

Because the scale can't tell you what you lost, and that's the only question worth asking.

Two people can lose the same six kilograms. One loses five of fat and one of lean, the other loses three and three. The scale says the same thing about both, and their next year looks completely different.

That's what a body composition scan is for. Monthly is often enough to see a trend, and the trend is what we act on rather than any single reading.

If the fat is coming down and the lean mass is holding, you're doing it right and you can stop worrying about the number on the scale.

Can I get it back?

Mostly, yes, and it's worth starting now rather than waiting until treatment ends.

Muscle responds to resistance training at every age, and it responds while you're losing weight, not only afterwards. Protein plus progressive resistance work is the whole answer.

It's slower than losing the fat was. Give it months rather than weeks, and judge it on strength and on your scans, rather than on the mirror.

The bottom line

Protein and resistance training are what protect your muscle while the weight comes off. Your body composition scan is what tells you whether it's working.