How Many Calories Should I Eat on Mounjaro? UK Guide

You've had your second injection and the hunger has gone quiet. Breakfast doesn't appeal. Lunch feels like an obligation you keep postponing. By eight in the evening you realise the day's food has amounted to a yoghurt and half a sandwich, and you can't work out whether that's brilliant news or a problem.

So you go looking, and the question you type is some version of how many calories should I eat on Mounjaro to lose weight without running myself into the ground. Most people on tirzepatide land on that question within the first month. Not because they want to count anything, but because the appetite signal they'd relied on their whole life has stopped reporting for duty.

How many calories should you eat on Mounjaro?

There isn't a Mounjaro-specific calorie number. The medication doesn't change the arithmetic of weight loss, it changes how easy that arithmetic is to live with. So the honest answer starts with standard NHS weight loss guidance and adjusts from there.

The NHS puts average daily energy needs at 2,000 calories for women and 2,500 for men, and advises anyone trying to lose weight to reduce their intake by around 600 calories a day. Do that subtraction and you get the numbers you'll see quoted across most UK pharmacy sites.

Treat that middle column as a rough landing zone, not a target to hit precisely. A 5ft 2in woman with a desk job and a 6ft man who lays bricks are both "average" on paper and nowhere near each other in reality.

The floor in the right-hand column matters more than most people realise, and we'll come back to it.

Work out your own number in three steps

If you want something better than an average, the calculation takes about two minutes. Start with your basal metabolic rate, the energy your body burns doing nothing but existing. The Mifflin-St Jeor equation is the one most UK dietitians use, and it's noticeably more accurate for people carrying extra weight than the older Harris-Benedict formula that still floats around online.

First, calculate your BMR.

For women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

For men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5

Then multiply that figure by your activity level. Sedentary, meaning a desk job and little deliberate exercise, is 1.2. Lightly active, so a walk or two most weeks, is 1.375. Moderately active, exercising three to five times a week, is 1.55. Very active, training six or seven days, is 1.725. Most people overestimate this. If you're unsure, drop a level.

Finally, subtract 600.

Take a 42-year-old woman weighing 92kg at 165cm tall, who works at a desk and walks twice a week. Her BMR comes out at 1,580. Multiplied by 1.375 for light activity, her total daily energy expenditure is roughly 2,170. Take off 600 and her starting target is about 1,570 calories a day.

Now a 55-year-old man at 118kg and 180cm, on his feet most of the day at work. His BMR is about 2,035. At 1.55 for moderate activity that's roughly 3,150, so his target lands near 2,550. Considerably more than the 1,900 average, and a fair illustration of why the average is only ever a starting point.

Both numbers are high enough to keep someone fed and low enough to lose weight steadily. Our full guide to calculating your BMR walks through the maths more slowly if you'd rather see it laid out.

Why the floor matters more than the ceiling

Advice for people on tirzepatide has to part company with ordinary diet advice at this point.

On a conventional diet, the enemy is eating more than you meant to. On Mounjaro, especially from 7.5mg upwards, plenty of people find the opposite. Food stops being interesting, the stomach empties slowly, and a day can pass on 700 or 800 calories without any conscious restriction at all. Patients often describe it with some surprise: they aren't white-knuckling anything, they simply forgot.

Sustained under-eating causes problems. Fatigue that doesn't lift. Hair shedding a few months in, which is often a delayed response to a steep energy deficit. Nutrient gaps, particularly iron, B12 and calcium, because there's no room in a 700-calorie day for everything a body needs. And a stall on the scales, which feels like the medication has stopped working when the actual problem is that you've asked your body to run a household on a fraction of its budget. If that pattern sounds familiar, our piece on why weight loss stops in a calorie deficit covers what to look at first.

NHS England is direct about this. Its guidance for clinicians prescribing tirzepatide asks behavioural support services to help patients maintain nutritional intake "in the context of reduced satiety", and to make sure people get adequate macronutrients and micronutrients from what has become a much smaller plate. The concern is written into the national pathway.

The signs are easy to miss because none of them look like hunger. Feeling cold when nobody else does. Climbing the stairs and needing a moment at the top. Losing more than about 1kg a week once you're past the first fortnight. Bruising more readily, or noticing that a cut takes longer to close over. Any of those, alongside a week of very small plates, is worth taking seriously.

So: 1,200 calories for women and 1,500 for men, as a routine floor. Going below that occasionally, on a bad nausea day, is not a crisis. Living there for weeks is worth a conversation with your prescriber.

Protein is the number that matters more than calories

If you only track one thing, track this.

Weight lost on a GLP-1 is not purely fat. In the body composition substudy of the SURMOUNT-1 trial, participants on tirzepatide lost 21.3% of their body weight over 72 weeks, and roughly three-quarters of that loss was fat mass with the remaining quarter coming from lean tissue. That ratio is broadly what you'd expect from any substantial weight loss. It's also the part you can influence.

Protein is the main lever. A review in the American Journal of Clinical Nutrition concluded that 1.2 to 1.6g of protein per kilogram of body weight per day supports the preservation of lean mass during energy restriction, while the standard 0.8g/kg is enough for losing weight but not enough to protect muscle.

In practice that means roughly 30 to 40g of protein at each meal, which is a chicken breast, or a tin of tuna and two eggs, or 200g of Greek yoghurt with a scoop of protein powder stirred through. When appetite is low, protein needs to go on the plate first, before the vegetables and before the carbohydrate, because it's the thing most likely to get crowded out.

Resistance training does the other half of the job. Two sessions a week is enough to change the outcome. We've written more on holding on to muscle while losing weight on a GLP-1, and if solid food is a struggle, protein shakes are a reasonable way to close the gap.

Your target moves as your dose goes up

Two things shift over the course of treatment, and they pull in opposite directions.

Appetite suppression deepens with each titration step. The 2.5mg starting dose is a four-week runway that barely touches hunger for some people. By 10mg or 15mg, the effect is a different order of magnitude. If you set a calorie target in month one and never revisit it, you may be well under it by month four without realising. Our Mounjaro dosage guide sets out what each step typically feels like.

At the same time, your energy needs fall. A smaller body burns less. Using the Mifflin-St Jeor coefficient, every 10kg you lose knocks roughly 100 calories off your resting metabolic rate before you account for the reduced effort of carrying yourself around. Lose three stone and the target that worked at the start is now noticeably too generous.

The practical version: rerun the calculation every stone, or every three months, whichever comes first. Adjust the number, then check that your protein target has moved with your weight too.

What to do when you can't physically eat enough

This comes up constantly and rarely gets a straight answer.

Smaller and more often works better than three meals. Four or five small plates spread across the day get more in than two large ones you can't face. Drink some of your calories, since a milk-based smoothie with yoghurt, oats and nut butter can carry 400 calories that a plate of the same food couldn't. Keep something easy in the fridge for the days when cooking feels like too much.

Watch what nausea is quietly steering you towards. Plain carbohydrate, toast and crackers and dry cereal, tends to feel most tolerable, which is exactly how a day ends up at 900 calories with 25g of protein in it. Our Mounjaro diet guide has a starter week built around this problem.

Two other things get mistaken for appetite loss. Dehydration blunts hunger and is easy to slip into when you're drinking less alongside eating less, so how much water you're getting is worth checking. So is constipation, which makes almost everyone feel too full to eat. Both are fixable, and both make the calorie question look harder than it is.

If you've tried all of that and still can't get past your floor for more than a week or two, tell your prescriber. Holding a dose rather than titrating up is a normal, sensible adjustment, not a failure.

Do you actually need to count calories on Mounjaro?

For a lot of people, no.

The medication is licensed as an adjunct to a reduced-calorie diet and increased physical activity, so the diet isn't optional. But "reduced-calorie" and "counted" aren't the same thing, and tracking every mouthful can be miserable for anyone with a history of disordered eating. If that's you, please talk to your clinician before starting any kind of log.

A middle path works well for most: track properly for two weeks, then stop. Two weeks tells you what your usual portions actually contain, whether your protein is anywhere near target, and whether your quiet days are quieter than you thought. After that, most people can eyeball it.

Weigh things during those two weeks rather than estimating, because portion sizes on packets are frequently smaller than the amount anyone actually serves. The NHS uses rice as the example: a packet may list a 75g portion at 260 calories, while the helping you cook comes out at 150g and 520. That gap is where a fortnight of careful logging earns its keep, and it cuts the other way too. People convinced they're eating 1,600 calories often find they're nearer 1,000.

Counting does earn its place in a few situations. If the scales haven't moved in six weeks on a stable dose. If you're feeling wiped out and suspect you're under-fuelling. If a clinician has asked you to track for a specific reason. And if you're heading into maintenance, where the target shifts from a deficit to a match and the margin for error narrows.

One thing counting won't fix is food noise, the mental chatter about food that many people find fades on tirzepatide. If it's still loud, that's information about your dose, not your diary.

This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting any treatment.