Already prescribed a GLP-1 or dual-agonist medicine such as semaglutide or tirzepatide? Use this free guide to protect your muscle while the weight comes off: a daily protein target, small high-protein meals for a low appetite, tips for common stomach side effects and a simple strength plan. It does not advise on whether to take these medicines or on doses.
A small-appetite day that hits it
| When | What to eat | Protein |
|---|
Eat the protein part of each plate first. Values are approximate (USDA) and vary by brand; check the label on shakes and powders.
Your strength starting point
Why protecting muscle matters on these medicines
Semaglutide (sold under brand names such as Wegovy and Ozempic) and tirzepatide (such as Zepbound and Mounjaro) cut appetite, so many people eat far less than before. Part of the weight that comes off is lean mass, which includes muscle. In the body-composition substudy of the STEP 1 trial, total fat mass fell by 19.3% and lean body mass by 9.7% with semaglutide. A 2025 joint advisory from four US nutrition and obesity societies worked out that, of an average 13.6 kg (30 lb) lost, about 5.3 kg (38%) was lean mass, and estimated that roughly a fifth of the total weight lost was muscle. In the SURMOUNT-1 body-composition study of tirzepatide, about 75% of the weight lost was fat and 25% was lean mass, a similar split to the placebo group.
Lean mass is not all muscle (it also includes water and organs), and some lean loss happens with any large weight loss: in SURMOUNT-1 the placebo group, who lost less weight with lifestyle changes, showed the same 75/25 split. But muscle keeps you strong, mobile and able to stay active, so it is worth protecting. The same advisory says that eating more protein alone is likely not enough: it recommends regular strength training at least 3 times a week plus at least 150 minutes of moderate aerobic activity, alongside adequate protein. WHO recommends muscle-strengthening activities for all major muscle groups on 2 or more days a week for every adult.
How the protein target is worked out
The joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society notes that targets of 1.2–1.6 g of protein per kg of body weight a day have been proposed during active weight loss. It also points out that using your full current weight can overestimate needs in people with obesity. So, exactly as in our protein calculator, if your BMI is above 30 we use a reference weight at a BMI of 25 for your height. Your target is the middle of that range, or the top of it if you already lift weights. The advisory also suggests a simple absolute target of 80–120 g a day, so we show how your number compares. It advises against long periods at or above 2 g/kg a day, and this tool stays below that.
Eating when your appetite is small
- Protein first. Start each meal with the protein part of the plate so it gets eaten before you feel full.
- Small and often. If you feel sick, small meals every 3–4 hours with enough fluids are easier than three big plates.
- Choose dense, low-volume protein. Fish, eggs, Greek yogurt, cottage cheese, nuts and seeds pack a lot of protein into a small portion. Lentils, beans, tofu, tempeh and edamame work for vegetarians and vegans.
- Drink some of it. A shake made with milk or soy milk and a scoop of protein powder is often easier than solid food on low-appetite days.
- Keep quality high. Favour dairy, seafood, eggs, poultry and plant proteins, with red and processed meats in moderation, and fill the rest of the plate with vegetables, fruit and whole grains.
For more ideas, browse our high-protein foods list or build a plate with the protein plate builder.
Fluids, fibre and common stomach side effects
Feeling sick, vomiting, diarrhoea, constipation and stomach pain are among the most common side effects of these medicines. Food and fluid habits can help, and your prescriber or pharmacist can advise if they don’t settle.
| If you have | What often helps |
|---|---|
| Nausea | Small, bland, low-fat meals such as toast, crackers or soup. Eat slowly, don’t lie down straight after eating and get some fresh air. Ginger or peppermint tea may help. Go easy on fatty and very high-fibre foods in the first few days after starting. |
| Constipation | Raise fibre gradually from vegetables, fruit (prunes and other dried fruit), beans, lentils, oats and whole grains, drink enough fluids and take a daily walk. Ask your pharmacist or doctor before using fibre supplements or laxatives. |
| Diarrhoea | Avoid large or high-fat meals and replace lost fluids. If it doesn’t stop, contact your prescriber, as it can lead to dehydration. |
| Not drinking enough | One NHS weight-management service advises 2–3 litres (about 8½–12½ cups) of water or sugar-free drinks a day while on tirzepatide, unless your doctor has told you to limit fluids. Our hydration calculator can help on training days. |
A beginner strength plan: 2–3 days a week
Do this on 2 non-consecutive days a week for the first two weeks, then add a third day, as the joint advisory suggests. Choose a weight you can lift 8–12 times with good form (the American College of Sports Medicine’s starting range for beginners). Do 1 set of each exercise at first, building to 2–3 sets. When 12 reps feel easy, add a little weight.
| Muscle groups | Day A | Day B |
|---|---|---|
| Legs (squat) | Sit-to-stand from a chair, then goblet squat | Split squat or step-up |
| Hips and back (hinge) | Glute bridge | Dumbbell Romanian deadlift |
| Chest and arms (push) | Incline or wall push-up | Dumbbell overhead press |
| Back (pull) | One-arm dumbbell row | Band row or lat pulldown |
| Core and grip | Farmer’s carry | Plank or dead bug |
See how to do each move in the exercise library, get a session built around your equipment with the workout generator, and when you are ready for a structured plan, move on to the 12-week strength program. New to training? Read how to start working out after 40 and strength training after 35.
Track the right things
The scale only tells you how much weight you lost, not what it was. Track these as well:
- Strength: note the weights and reps you lift. Holding or improving them is a good sign you are keeping muscle.
- Waist: measure every 2–4 weeks and check your waist-to-height ratio.
- How clothes fit, your energy and how you sleep.
- Protein and training days: how many days a week you hit your target and lifted.
Log it all in our free progress tracker, and read how to lose fat and keep muscle after 35.
When to call your doctor or get urgent help
Contact your prescriber, pharmacist or local urgent care service (NHS 111 in England) straight away if you have:
- Severe pain in your stomach area that will not go away, with or without vomiting, sometimes spreading to your back (a possible sign of pancreatitis).
- Pain in your upper stomach, yellow skin or eyes, fever or pale, clay-coloured stools (possible gallbladder problems).
- Nausea, vomiting or diarrhoea that will not go away, or signs of dehydration: very dark pee or peeing much less than usual, dizziness when you stand that does not pass, unusual tiredness or confusion.
- Signs of low blood sugar if you also take insulin or a sulfonylurea: shakiness, sweating, dizziness, confusion or blurred vision.
- Changes in your vision, or new, worse or worrying changes in your mood.
Also tell every healthcare provider that you take one of these medicines before any planned surgery or procedure. Women using tirzepatide should ask about contraception, because the prescribing information says birth control pills may not work as well after starting and after each dose increase.
Call your emergency number (911, 999 or 112) if you have swelling of your face, lips, tongue or throat, trouble breathing or swallowing, a very fast heartbeat or you feel faint.
Only use these medicines as prescribed for you and dispensed by a licensed pharmacy. Regulators warn that unapproved and counterfeit versions sold online may contain the wrong ingredients.
Sources
- Mozaffarian et al. (2025), American Journal of Clinical Nutrition: Nutritional priorities to support GLP-1 therapy for obesity, joint advisory from ACLM, ASN, OMA and TOS
- Wilding et al. (2021), New England Journal of Medicine: once-weekly semaglutide in adults with overweight or obesity (STEP 1), including the DXA body-composition substudy
- Look et al. (2025), Diabetes, Obesity and Metabolism: body composition changes with tirzepatide in the SURMOUNT-1 study
- US FDA: Wegovy (semaglutide) prescribing information and medication guide
- Zepbound (tirzepatide) medication guide, FDA-approved patient information
- NHS: tirzepatide, side effects and when to get help
- Cambridge University Hospitals NHS: your obesity treatment with tirzepatide, managing side effects and fluids
- NHS 111 Wales: symptoms of dehydration in adults
- US FDA: concerns with unapproved GLP-1 drugs used for weight loss
- World Health Organization: physical activity recommendations for adults
- American College of Sports Medicine (2009): progression models in resistance training for healthy adults
- National Academies: Dietary Reference Intakes for fibre and macronutrients
- USDA FoodData Central (SR Legacy): protein content of the foods
This guide gives general education, not medical advice, and is not affiliated with any drug maker. Brand names belong to their owners. Always follow the advice of the clinician who prescribed your medicine, and check with them before changing your diet or starting exercise, especially if you have a health condition.
More free tools: Protein calculator · Macro calculator · Progress tracker · Workout generator · All tools