Protein on GLP-1 medication: how much and UK sources

Why everyone suddenly wants to talk to you about protein

If you're on a GLP-1 medication — Mounjaro, Wegovy or similar — you've probably been told to "get your protein in" by roughly everybody, usually without anyone explaining how much, or what that looks like when you're standing in front of the fridge with no appetite. So let's do the useful version.

Here's the short of it. When weight comes off, some of what you lose is fat and some of it is lean tissue — muscle included. That's true of every method of losing weight quickly, including very-low-calorie diets and surgery. It matters more here because appetite is small enough that protein is often the first thing to fall out of the day.

Protein, alongside actually using your muscles, is how you hold on to that lean tissue. That's the whole argument.

What the evidence actually shows

Across weight-reduction studies of all kinds, 11–50% of the weight lost can be lean body mass — a wide range, because it depends enormously on how fast the weight comes off, how little you eat, and whether you're doing any resistance work.

The joint advisory from four US nutrition and obesity bodies puts numbers on it. In the semaglutide trial, 5.3kg of the weight lost was lean body mass — about 38% of the total. Since roughly half of lean body mass is muscle, that works out at around 20% of total weight lost being muscle. Modelling suggests muscle accounts for 10–15% of total weight lost in women and 20–25% in men in the absence of structured exercise. That last clause is the actionable part of the sentence.

There's also a measured gap between advice and practice. Overall energy intake on these medicines falls by 16–39% — and in one of the studies in that review, protein intake fell by around 17% too. Protein doesn't protect itself.

And it's the official UK position that these medicines come with food and activity support, not instead of it. The British Dietetic Association and British Nutrition Foundation say in their joint position statement that people should have "dietary and physical activity advice, that promotes maintenance of muscle mass and function", and that "people should not be prescribed the medication alone".

So how much protein do you actually need?

Two numbers get quoted at you, and they answer different questions.

The UK reference intake is 0.75g per kilogram of body weight a day — about 45g a day for an average woman and 56g for an average man. That figure exists to prevent deficiency in the general, weight-stable population. It was never designed as a target for someone losing weight quickly on a medication that has flattened their appetite.

During active weight loss, higher targets of around 1.2–1.6g per kilogram a day are commonly proposed. For a 90kg person that's roughly 110–145g. The same advisory is clear about the boundaries in both directions: don't let intake fall below 0.4–0.5g/kg, and don't sit above 2g/kg for long periods either — more is not better.

Please don't get too hung up on the numbers. Some online calculators will hand you a daunting figure like 200g, which is hard to achieve and not necessary for most people.

Here's how I handle it in practice. I'd rather you reliably hit a floor of around 60g a day — a palm-sized portion of protein at two to three meals — than aim at 145g, miss it, and feel you've failed by Wednesday. Sixty grams is a realistic, defendable minimum when appetite is genuinely small. If you're eating comfortably, doing resistance work, or you're older, the number I'd want for you sits higher — and that's a conversation about your body rather than a number read off a website.

What protein looks like in ordinary UK food

This is the bit that changes anything. "30g of protein" means nothing in a kitchen. Here's what it looks like on a plate.

A few more that live in most fridges: a 145g tin of tuna in spring water is around 26g, a 150g pot of Greek-style yoghurt around 15g, 100g of cottage cheese around 12g, 100g of firm tofu around 15g, 200ml of semi-skimmed milk around 7g and 30g of cheddar around 7.5g.

So two eggs on granary toast with half a tin of beans gets you to roughly 30g at breakfast. A palm of chicken with lentils stirred through the sauce does something similar at dinner. Add a yoghurt and a glass of milk across the day and you're at your floor without a shaker bottle in sight.

Making it work on a small appetite

• Protein first on the plate. If you're only going to manage half of what's in front of you, make the half you eat the half that counts. Eat the chicken before the potatoes.
• Drink some of it. Milk, milky coffee, a yoghurt drink, a smoothie made with milk or yoghurt. On days when chewing feels like work, liquid protein is the most reliable route in.
• Spread it out. Two to three protein portions across the day suits your muscles better than loading everything into dinner.
• Keep the easy stuff in. Tinned fish, eggs, ready-cooked chicken, frozen prawns, tinned beans and lentils, longlife milk. When appetite is low, the deciding factor is almost always what needs no effort.
• On the days nothing appeals at all, protein is the second priority — fluid comes first. There's more on that in what to eat on Mounjaro when nothing appeals.
• Batch it when you feel well. The version of you who feels fine on a Sunday can cook for the version who doesn't on Wednesday.

Protein alone doesn't do it

This is the part that gets left out. Protein gives your body the material; using your muscles is what tells it to keep them. Structured resistance training — or resistance plus aerobic — is well established for preserving lean mass during weight loss, and aerobic exercise on its own has a noticeably smaller effect. The UK guidance is muscle-strengthening activity on at least two days a week, and it doesn't have to mean a gym: carrying shopping, standing up out of a chair without using your hands, resistance bands in front of the television, a set of stairs. Two sessions of something beats none, and for most people reading this it's the highest-value thing they aren't doing.

What about protein shakes and "high protein" products?

They're a tool, not a requirement. A balanced diet gives most people everything they need, and real food brings the fibre and micronutrients a shake doesn't. That said, if a shake is the only thing that goes down at 7am during a step-up week, a shake is a perfectly sensible answer — I'd rather that than nothing.

Be a bit sceptical of "high protein" on things that are essentially confectionery. The label rule is that high protein means 20% or more of the energy comes from protein — worth a glance at what else is in there.

If you want this worked out for your body

Everything above is general. How much protein you need depends on your weight, your appetite, what else you're managing and what you're doing with your muscles — and it's the kind of thing that takes twenty minutes to settle properly and then stops being a worry.

If you'd like to talk it through, that's what a free 15-minute call is for.

Sources

1. Christensen S, Robinson K, Thomas S, Williams DR. Dietary intake by patients taking GLP-1 and dual GIP/GLP-1 receptor agonists: a narrative review and discussion of research needs. Obesity Pillars 2024;11:100121. doi.org/10.1016/j.obpill.2024.100121
2. Mozaffarian D, Agarwal M, Aggarwal M, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society. Obesity 2025;33:1475–1503. doi.org/10.1002/oby.24336
3. British Dietetic Association / British Nutrition Foundation. Joint position statement regarding weight loss drugs in people living with obesity and/or type 2 diabetes, April 2024. nutrition.org.uk
4. British Nutrition Foundation. Protein — UK Reference Nutrient Intake 0.75g/kg body weight/day. nutrition.org.uk/nutritional-information/protein
5. UK Chief Medical Officers' Physical Activity Guidelines — muscle-strengthening activity on at least two days a week. gov.uk