The 30-second summary
- There is no official calorie number for any GLP-1 medicine. A sensible target starts from what your body burns each day and takes off a modest deficit.
- Appetite often decides the total. These medicines cut how much people eat, sometimes below any target. When that happens, protein matters more than calories.
- Stay above the floor. An expert advisory warns that intakes under about 1,200 kcal a day for women and 1,800 kcal for men make it hard to get enough vitamins and minerals.
Why there is no official number
Wegovy's UK prescribing information describes it as an addition to "a reduced-calorie diet and increased physical activity". The NHS says you will need to eat a healthy, balanced diet while using semaglutide. Neither gives a figure, and for a good reason: the right number for a 60 kg woman who sits at a desk is not the right number for a 110 kg man who works on his feet.
The NHS does give a general guide. An average woman needs about 2,000 kcal a day and an average man about 2,500 kcal, and it says plainly that your own figure could be different depending on your age, weight, height and how much exercise you do. On a GLP-1 medicine, you want your own figure.
How a calorie target is worked out
The foodose calculator does it in three steps, and you can check each one on the method page.
- What you burn at rest. This comes from the Mifflin-St Jeor equation, which uses your weight, height, age and sex.
- What you burn in a day. The resting figure is multiplied up for how active you are.
- A modest deficit. A planned loss of half a kilo a week works out at about 550 kcal a day, using the common rule of 7,700 kcal per kilogram. The calculator keeps the target between 70% and 90% of what you burn, and never below 1,200 kcal for women or 1,500 kcal for men.
Two honest caveats. First, if you have already lost more than 5% of your starting weight, the calculator lowers its estimate of what you burn a little, because the body adapts as weight comes off. Second, the 7,700 kcal rule is a planning convention, not a promise. Modelling work led by Kevin Hall found that body weight responds slowly to a change in how much you eat, taking about a year to get half of the way to where it will settle. Weight loss slows over time even when you eat the same amount, and that is expected, not a failure.
Why you may not reach your target
GLP-1 medicines reduce appetite, and trials have measured how much less people eat as a result:
- Semaglutide 1 mg. After 12 weeks, people ate 24% less in total across a day of free-choice meals than they did on placebo.
- Semaglutide 2.4 mg. After 20 weeks, people ate 35% less at a free-choice lunch than on placebo.
- Tirzepatide. At week 3 of a phase 1 trial, people ate about 525 kcal less at a free-choice lunch than on placebo.
The calculator turns findings like these into an appetite ceiling: an estimate of the most you are likely to manage at your dose. When the ceiling sits above your target, the target is the number to aim for. When it sits below, your appetite is likely to decide the total, and chasing the calorie figure is the wrong instinct.
What the numbers look like
These are six worked examples from the calculator, each for a lightly active adult. Follow a link to see who the example is and the arithmetic behind every figure.
| Worked example | Calorie target | Appetite ceiling | Protein floor | Likely to set the total |
|---|---|---|---|---|
| Wegovy 1 mg, 88 kg | 1,568 kcal | about 1,609 kcal | 118 g | The target |
| Wegovy 2.4 mg, 95 kg | 1,669 kcal | about 1,443 kcal | 133 g | Appetite |
| Ozempic 1 mg, 82 kg | 1,488 kcal | about 1,549 kcal | 111 g | The target |
| Mounjaro 7.5 mg, 100 kg | 1,759 kcal | about 1,501 kcal | 133 g | Appetite |
| Mounjaro 15 mg, 92 kg | 1,639 kcal | about 1,095 kcal | 129 g | Appetite |
| Zepbound 10 mg, 110 kg | 2,214 kcal | about 1,658 kcal | 160 g | Appetite |
Look at the last column. At lower doses and smaller bodies the target and the ceiling sit close together. At the top of the tirzepatide range the ceiling falls well below the target, and appetite, not arithmetic, sets the day.
The floor to stay above
Eating very little is not a faster route to anything good. A 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society warns that the large, rapid drop in intake on these medicines can leave people short of vitamins and minerals, especially below about 1,200 kcal a day for women and 1,800 kcal for men.
The signs it lists include tiredness beyond what you would expect, a lot of hair loss, flaky or itchy skin, muscle weakness, wounds that heal slowly and bruising easily. If you notice them, talk to your prescriber. (See nutrient gaps on a GLP-1.)
Nausea, vomiting and diarrhoea can also cost you fluid. The prescribing information for both semaglutide and tirzepatide warns about dehydration and advises taking care to avoid it. If you cannot keep fluids down, contact your prescriber or NHS 111.
When calories and protein disagree, choose protein
On a small appetite, the calorie total is the least useful number to chase. The advisory suggests eating protein-rich foods first in a meal, so they get eaten before fullness arrives. Then fibre and fluid. Then whatever else you can manage.
In practice that means a plate that starts with chicken, fish, eggs, Greek yoghurt, cottage cheese, tofu or lentils, and a day where the protein floor is the target you actually track. The under 400 calorie GLP-1 recipes and the high-protein GLP-1 recipes are built for exactly that kind of day. (See protein on a GLP-1.)
What to do with this
A general number is a starting point, not yours. The calculator works out your calorie target, your protein floor and your appetite ceiling from your own weight, height, age, activity, medicine and dose, and shows its working.
Sources
- Wegovy 2.4 mg FlexTouch solution for injection in pre-filled pen: Summary of Product Characteristics. electronic medicines compendium. emc
- NHS. Semaglutide. nhs.uk
- NHS. Understanding calories. nhs.uk
- Mifflin MD, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990. PubMed
- Greenway FL. Physiological adaptations to weight loss and factors favouring weight regain. Int J Obes 2015. PubMed
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011. PubMed
- Blundell J, et al. Effects of once-weekly semaglutide on appetite, energy intake, control of eating, food preference and body weight in subjects with obesity. Diabetes Obes Metab 2017. PubMed
- Friedrichsen M, et al. The effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying in adults with obesity. Diabetes Obes Metab 2021. PubMed
- Martin CK, et al. Tirzepatide on ingestive behavior in adults with overweight or obesity: a randomized 6-week phase 1 trial. Nat Med 2025. PubMed
- Mozaffarian D, 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 Pillars 2025. PubMed
- Mounjaro KwikPen solution for injection in pre-filled pen: Summary of Product Characteristics. electronic medicines compendium. emc
Medical disclaimer: Articles in the foodose research library are educational, not medical advice. Talk to your prescriber or a dietitian about your own nutrition. See our full medical disclaimer.