How Much Protein on a GLP-1? The Numbers That Protect Muscle

Short answer: eat at least 1.2g of protein per kg of body weight a day. Make it 1.6g/kg if you’re lifting at all. For someone at 90kg, about 14 stone, that’s 108g to 144g daily. Split it across four feeds of 25g to 30g.

Why split it? Not because your body can’t handle a big dose. Because appetite-suppressing medication leaves you no room for one.

Protein calculator: how much protein do you need a day?

The muscle you lose is not a rounding error

The trials that made these drugs famous also body-scanned some of the people taking part. That’s how we know what the weight was actually made of.

In STEP 1, the big semaglutide trial, those scans showed 6.9kg of lean tissue lost alongside 10.4kg of fat. That’s about 40% of the total weight lost.

Tirzepatide looked kinder. In the SURMOUNT-1 scans the split was 5.6kg lean against 15.9kg fat, roughly 26%.

A review in Metabolism pooled 22 trials covering 2,258 people. Across the whole class of drugs, it put lean tissue at about a quarter of the weight lost.

One caveat: 40% is the scariest number here, and two things take the edge off it.

First, everyone who gets meaningfully smaller loses some lean tissue. It isn’t unique to the medication. Part of that “lean” figure is water and organ mass rather than muscle.

Second, in STEP 1 the proportion of the body made of lean tissue went up, because fat came off faster. Body composition improved.

So why act on it at all? Because of how little people eat on these drugs.

A 2025 study in the Journal of the International Society of Sports Nutrition measured intake in 60 adults using GLP-1 medication. Men averaged 88g of protein a day and women 74g. Only 43% cleared the 1.2g/kg floor, just 10% reached 1.6g/kg, and 5% reached 2.0g/kg.

The drug does its job on appetite. Total intake falls, and protein falls with it unless you protect it on purpose.

There’s a name for where that leads. Sarcopenic obesity is low muscle mass and strength sitting alongside excess fat. It got a formal definition in the 2022 ESPEN and EASO consensus statement, and it’s a worse place to land than where most people start.

Lean mass also drives your resting metabolic rate, which is the calories you burn doing nothing. Lose weight and that rate falls.

A 2022 study in the International Journal of Obesity worked out why. About 60% of the fall was losing calorie-hungry tissue. The other 40% was the body quietly running more efficiently.

Keep the scale of it in mind. The whole fall came to about 101 kcal a day after losing 7.3kg. Worth protecting, but it isn’t proof your metabolism is broken.

The protein target, and where it comes from

Here’s the honest position: no trial has settled how much protein you need on a GLP-1.

The authors of a 2025 International Journal of Obesity paper say so themselves. They call the right dose during GLP-1 use an urgent gap in the research.

What we have instead are two proposals, borrowed from people with the same problem after weight-loss surgery:

• 0.8g to 1.6g per kg a day, or 80g to 120g a day in plain grams
• 1.2g to 2.0g per kg a day based on adjusted body weight while eating in a deficit

Here’s where it gets misread. Adjusted body weight is a calculation used for people well above their ideal weight. It isn’t the number on your scale.

Apply 2.0g/kg to a 130kg starting weight and you get 260g of protein a day. That’s neither achievable on a suppressed appetite nor what the guidance meant.

So here’s what it looks like at real body weights:

If you started heavy, lean on the 80g to 120g anchor more than the per-kg sum. Take the floor column seriously before you chase the target column.

Hitting 1.2g/kg every day beats aiming at 1.6g/kg and landing on 0.9g/kg three days out of five.

Why 25g to 30g at a time beats one big hit

The usual explanation is that GLP-1s slow your digestion to a crawl, so protein has to be drip-fed or it goes to waste. That’s not quite right, and the real reason is more useful.

These drugs do slow gastric emptying, which is the rate food leaves your stomach for your gut. That’s part of how they blunt your appetite. But the slowdown is smaller than the folklore suggests.

Researchers measure it by timing how fast you absorb paracetamol. Those studies put the delay mostly in the first hour after eating. Total absorption over five hours was unchanged.

On long-acting drugs like semaglutide the effect also fades over months, though some of it stays. That comes from a 2025 review in the Journal of Clinical Endocrinology & Metabolism.

The short version: your protein isn’t going to waste.

The real case for splitting it is muscle. Schoenfeld and Aragon’s 2018 paper in the Journal of the International Society of Sports Nutrition landed on 0.4g per kg per meal across at least four meals.

That’s the practical way to reach 1.6g/kg and get the best muscle-building response, rather than packing it into one or two big meals. For most adults it works out at 25g to 35g of good protein per feed.

That suits a suppressed appetite rather well. Four modest feeds are doable when one large dinner isn’t.

Protein alone won’t do it, so lift

Protein only supplies the raw material. Resistance training is the signal that tells your body the muscle is worth keeping. Without it, the protein does far less for you.

The research on holding on to muscle through GLP-1 weight loss is blunt about this. Resistance training, 3 to 5 days a week, is the most powerful tool there is that isn’t a drug. Every set of nutrition recommendations for this group pairs the protein target with it.

You don’t need a bodybuilding programme. Two or three sessions a week covering the major movement patterns will do. Take them close enough to hard that the last few reps are genuinely difficult.

Weight training beats cardio for this job. The protein and lifting combination is what the evidence supports, not either one on its own.

Which protein goes down when your appetite doesn’t

Once you accept that you need 25g to 30g a feed on a stomach that doesn’t want it, format matters more than brand. Three are worth knowing.

Whey protein isolate. Filtered to strip out most of the fat and lactose, which is the whole point when you feel sick. MyProtein’s Impact Whey Isolate lists 26g of protein per 30g scoop at 82g per 100g, with under 0.5g of fat and 0.6g of sugar.

Optimum Nutrition’s Gold Standard leads its blend with isolate and lists 24g per serving plus 5.5g of naturally occurring BCAAs. It’s a blend rather than a pure isolate, so it carries more lactose than the isolate above.

Clear whey. Mixes like a cordial rather than a milkshake. That helps when the thought of a thick, creamy drink turns your stomach, which is a common complaint on these drugs.

MyProtein’s version lists 20g of protein per 25g serving at 83 kcal, with no fat and no sugar. You pay more per gram of protein for the texture.

Essential amino acids. A fair fallback on days when nothing else will go down. They cost a lot per gram, and the evidence favours whole protein where you can manage it. Treat them as a gap-filler, not a plan.

✓ marks the better figure in each row. Prices on both move constantly, so don’t read the table as a permanent ranking.

Do this instead. Divide the price by the grams in the tub, then by the protein percentage on the label. That gives you cost per 100g of protein, the only number that compares products honestly.

Anything sold as “was £67.99, now £48.99” deserves the same arithmetic rather than the benefit of the doubt.

Want to compare more widely first? Our guide to the best protein powders for weight loss goes deeper on isolate versus concentrate. There’s also a wider range of whey isolate on Amazon UK if you want to see the field.

Hitting the number without feeling stuffed

Practical tactics, roughly in order of how much they help:

• Front-load the day. Appetite suppression is usually weakest first thing, before the day’s nausea builds. A high-protein breakfast or a shake before 9am banks 25g to 30g while it’s still easy.
• Upgrade what you already drink. Oats cooked in high-protein milk. Coffee with a scoop of collagen or whey. Soup with a spoon of skimmed milk powder stirred through. Same calories, more protein.
• Spend your appetite on the protein first. When you can only manage half a plate, eat the chicken, white fish or turkey before the potatoes. The highest-protein foods earn their place on a small plate.
• Cold and thin beat hot and thick. Nausea puts up with a chilled clear drink far better than a warm, creamy one. Ice helps more than flavour does.

The bottom line

The scale going down is the easy part on these drugs. Keeping the muscle underneath it decides whether you end up strong and smaller, or just smaller.

Get to 1.2g of protein per kg as a floor, and 1.6g/kg if you train. Split it across four feeds of 25g to 30g so it’s actually achievable. Then lift something heavy two or three times a week.

Pick whichever protein format you’ll finish. Isolate if creamy drinks still work for you, clear whey if they don’t. Judge it on cost per 100g of protein rather than the sticker price.

Ready to choose one? Our head-to-head on MyProtein vs Optimum Nutrition runs both brands through the same per-protein maths. The 2026 protein powder brand rankings widen the field if neither suits.

This is nutrition guidance, not medical advice. Anything to do with your dose, your side effects, or whether a GLP-1 medication is right for you belongs with the clinician who prescribed it.