Why GLP-1 users need different math
Every traditional calculator helps people eat less. On GLP-1 medications the problem inverts: appetite suppression makes it hard to eat enough — and studies of rapid weight loss consistently find that without countermeasures, a meaningful fraction of the weight lost (commonly cited at 25–40%) can be lean tissue, not fat. The two evidence-based countermeasures are a high protein intake and resistance training. This calculator runs that logic in the right order: protein is locked first, then fat for hormones and absorption, and whatever calories remain go to carbohydrate.
The protein numbers, honestly sourced
The target is 1.6–2.2 g of protein per kilogram of lean body mass — the range supported by muscle-retention research during energy deficits. (Beware advice quoting grams per pound of lean mass; at suppressed appetites those targets are physically impossible and discredit themselves.) Your lean mass comes from your body fat percentage if you know it — the body fat calculator takes two minutes with a tape measure — or is estimated with the Boer formula if you don't.
What the warnings mean
If your real-world intake can't fit the protein floor plus essential fat, or sits below commonly cited safe minimums, this tool says so plainly and points you to your prescriber or a registered dietitian — because dose, timing and nutrition support are medical decisions, not calculator outputs. Rapid loss beyond ~1.5% of bodyweight per week also gets flagged, since lean-loss risk climbs sharply past that pace.
Make the plan work in practice
Eat protein first at every small meal, lean on protein-dense and liquid options when solid food is hard, train with resistance 2–3 times a week, and verify reality monthly: the actual TDEE calculator turns your logged intake and scale trend into your true burn. The full playbook is in our guide to avoiding muscle loss on GLP-1 medications.
This tool supports nutrition planning during medically supervised weight loss. It is not medical advice and never replaces guidance from your prescriber, pharmacist or dietitian.
Frequently asked questions
How much protein should I eat on Ozempic or Zepbound?
The research-supported range during rapid weight loss is 1.6–2.2 g per kilogram of lean body mass per day — for most people roughly 90–150 g. Spread it across your small meals, protein first on the plate.
I can't physically eat that much protein. What now?
Prioritise protein-dense foods (Greek yogurt, eggs, lean meats, cottage cheese), use liquid protein when solids are hard, and raise it with your care team — dietitians routinely solve this, and dose timing can sometimes help. Don't quietly accept months below the floor.
Do I really need to lift weights on GLP-1 medication?
Resistance training is the other half of muscle preservation — protein provides the bricks, training provides the signal to keep them. Two to three sessions a week of basic, progressive work is the evidence-based minimum.
Is losing weight fast on GLP-1 medication dangerous for muscle?
Faster loss means a larger share tends to come from lean mass, especially without protein and training. Beyond roughly 1.5% of bodyweight per week, the risk climbs — worth discussing pace with your prescriber rather than maximising it.
More calculators
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BMR Calculator
Estimate the calories your body burns at complete rest, compared across the three standard equations
Calorie Deficit Calculator
Choose a weekly weight-loss rate and see the exact daily calories that achieve it
Macro Calculator
Split your daily calories into protein, carbs and fat
Maintenance Calorie Calculator
Find the daily calories that keep your weight stable
Sources
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021. [link]
- Mettler S, Mitchell N, Tipton KD. Increased protein intake reduces lean body mass loss during weight loss in athletes. Med Sci Sports Exerc. 2010. [link]
- Morton RW, Murphy KT, McKellar SR, 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. Br J Sports Med. 2018. [link]
- World Health Organization. WHO guidelines on physical activity and sedentary behaviour. 2020. [link]