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Exercise on Mounjaro is about keeping muscle, not burning calories
Here's the thing most people miss. When you eat a lot less, some of the weight that drops is muscle, not fat. It happens on any diet. Mounjaro and exercise work well together because the medicine handles the appetite side while movement protects the tissue underneath.
That matters more than people think. Muscle keeps your metabolism ticking over, so the more you hold onto, the more fuel you burn even sitting on the sofa. Lose it and your body quietly lowers the bill. That's exactly how the weight creeps back once you stop.
In the SURMOUNT-1 trial, Mounjaro led to average weight loss of up to 20.9% of body weight at 72 weeks. A chunk of that can come from muscle rather than fat if you don't lift anything. You can read more about how the medicine itself works in our guide to buying Mounjaro.
Strength training is the part most people skip, and it's the part that matters
Cardio gets the glory because it makes you sweat. It's good for your heart and lungs, and it does help with weight loss. But cardio alone won't protect your muscle the way resistance work does.
The good news is you don't need a gym, a trainer, or anything that plugs in. Squats, lunges, press-ups against the wall, and a pair of resistance bands cover most of it. Two short sessions a week is enough to make a real difference.
The NHS guidance backs this up. Aim for 150 minutes of moderate activity a week, like a brisk walk, or 75 minutes of vigorous activity, and add strength exercises on two days. Most people I speak to are doing the cardio and quietly dropping the lifting.
You don't need a gym membership or a marathon
A patient of mine with type 2 diabetes lost about a quarter of his body weight over nine months on Mounjaro. His exercise was walking and a bit of hiking. No marathons, no daily hour on the treadmill, no one shouting at him to push harder.
The lesson isn't that you should do nothing. It's that moderate, consistent movement beats a punishing regime you'll abandon by February. A brisk walk most days, cycling, swimming, a bit of yoga. All of it counts.
Start small. Ten to twenty minutes of light activity a few times a week is plenty in the first fortnight while your body settles in. You can build from there.
Protein and water do the other half of the job
Strength training tells your body to keep the muscle. Protein gives it the raw material to actually do it. The two go together, and skipping either one wastes the other.
Aim for at least 0.8 grams of protein per kilogram of body weight a day, more if you're training. That's a chicken breast, a fish fillet, a tub of Greek yoghurt, and some lentils spread across the day. I've written a longer guide to what to eat on Mounjaro if you want the full plan.
Water is the bit everyone forgets. Mounjaro can dull your sense of thirst, so you can be dehydrated mid-workout without feeling especially thirsty. Drink before, during, and after. It's the boring advice that prevents the most avoidable problems.
When to take it easy, and when to stop
In the first two to three weeks, nausea and low energy are common. That's not the moment for a personal best. Keep it gentle, and don't train on the day you inject, when the nausea is usually at its worst. The day after is often easier. If you want the full list of what's normal and what isn't, I've covered slimming injection side effects separately.
A few warning signs mean stop and get help. Severe pain in the upper part of your stomach that spreads to your back can be pancreatitis. Persistent vomiting you can't keep water down with, or feeling faint and unusually weak, should be checked. Call NHS 111 for advice, or 999 if it's sudden and severe.
And to be straight about it, Mounjaro isn't for everyone. It's prescribed for adults with a BMI of 30 or above, or 27 and above with a weight-related condition like high blood pressure or type 2 diabetes. The NICE guidance is clear on that. If you're pregnant, breastfeeding, or you've had pancreatitis or a certain type of thyroid cancer, it's off the table. A proper online assessment tells you before a single pen leaves the pharmacy.
Cost-wise, Mounjaro starts at £174.99 a month, with the assessment, prescription, and cold-chain delivery all included. No hidden fee at checkout, which shouldn't be a selling point but somehow is.
