Introduction
On a weight loss jab? Here's how to lose fat, not muscle:
Weight loss jabs are everywhere. Friends are on them, colleagues are on them, and the results can be dramatic. If you're on Mounjaro or Wegovy, or thinking about it, I'm not here to talk you out of it. For the right people, these medicines have their place.
But there's a question hardly anyone asks when they start: what are you actually losing? And the one that follows: what happens when you stop?
Weight Loss Jabs and Muscle Loss
What are GLP-1 weight loss jabs?
GLP-1 medicines copy a hormone your gut releases after you eat. It tells your brain you're full and slows down how quickly your stomach empties. The two you'll hear about most in the UK are:
- Wegovy (semaglutide), a weekly injection
- Mounjaro (tirzepatide), a weekly injection that also acts on a second hormone, GIP
The effect is simple: you feel less hungry, so you eat less, so you lose weight. And they work. In the main semaglutide trial, people lost an average of 17.3% of their body weight over 68 weeks (Wilding et al., Diabetes, Obesity and Metabolism, 2022).
Many people pay privately, typically around £130 to £350 a month depending on the dose, according to a September 2026 UK price comparison. The NHS is rolling Mounjaro out slowly. Under NHS England's guidance, GP prescribing in the first year is limited to people with a BMI of 40 or more (lower for some ethnic groups) and at least four weight-related health conditions, widening over the next few years.
What the jab doesn't do is choose what you eat, build your strength, or teach you how to live once you stop. It turns the volume down on hunger. Everything else is still down to you.
Why a jab on its own isn't enough
You can lose both muscle and fat. When you're barely hungry, it's easy to eat very little, and protein is usually the first thing to go. A 2025 review in Acta Diabetologica found that around a quarter to a third of the weight people lose from these jabs can be lean mass, including muscle. That's the muscle that keeps your metabolism ticking over, protects your joints, and keeps you strong as you get older. Lose too much of it, and you can end up lighter but weaker, and softer rather than toned.
The weight tends to come back when you stop. In the follow-up to the main semaglutide trial, people who stopped their injections had regained around two-thirds of the weight they'd lost within a year. The jab turned their hunger down. When it stopped, their hunger came back, and nothing else had changed.
That's the bit that worries me most...
As I see it, a jab suppresses your appetite, but it doesn't teach you anything. If you haven't changed how you eat while you're on it, you can still smash into a family-sized bar of chocolate and lose weight. So what happens the moment you stop? What's the plan for coming off? And once you've hit your goal weight, what then?
The support around it is patchy. NHS England guidance says that everyone prescribed Mounjaro by their GP must receive wraparound support, including dietary advice and help with changing habits. That's a good start. But it isn't someone in the gym with you twice a week, making sure you're building strength while the weight comes off. And if you're paying privately, you may get nothing at all beyond the pen and a check-in.
How to protect your muscle and keep the weight off
The research points to the same two things I've been banging on about for years: resistance training and enough protein. Here's how I work with people on a jab.
1. Start with the real numbers. Everyone begins with a two-hour consultation. I take body measurements, body fat, blood pressure, lung capacity, and photos. On a jab, that matters more than ever, because the scales can't tell you whether you've lost fat or muscle. Body fat measurements can. We repeat them every three to four months, so you can see what's actually changing.
2. Lift, don't just shrink. You'll train with me twice a week, built around proper strength work. Lifting tells your body to hold on to its muscle while the fat comes off. The aim isn't just a smaller you. It's a stronger one.
3. Make every mouthful count. When your appetite is low, what you do eat has to work hard. I don't hand out meal plans that last two days. Instead, you'll send me photos of what you eat, and I'll help you get the protein, vitamins, and nutrients your body needs. If the photos stop coming, I'll be on to you.
4. Learn it, so it lasts. Knowledge is power. I'll teach you how your body works: what visceral fat is, what a healthy body fat looks like for you, and how the little things add up. There was a TV documentary where a mum couldn't understand why she wasn't losing weight. It turned out she was eating an extra 2,500 calories a day just from picking at the kids' leftovers. Small habits like that don't disappear because you're on a jab. They're waiting for you when you come off.
5. Plan your exit from day one. We'll talk about your goal, what your ideal weight looks like, and how you'll live when the injections stop. By the time you come off, the habits, the strength and the knowledge are already yours.
I'm upfront about one thing. You'll earn every pound you lose. But you'll be glad you did.
Who this is for
This kind of support is for you if:
- You're on Mounjaro, Wegovy, or another GLP-1 jab and want to make sure you're losing fat, not muscle
- You're about to start one and want to get it right from the beginning
- You're planning to come off, and you're worried the weight will come back
- You're paying a lot of money every month and want the results to last
- You're ready to put the work in, not just wait for the pen to do it
It's not for you if you want a quick fix before a wedding or a holiday. There are plenty of trainers who'll do that. I'm interested in long-term change.
I train people in person at my private gym in Mortimer Common, near Reading. If you're further afield, I also offer online personal training.
And a word of care: your jab is a medicine. Anything to do with your dose, side effects, or when to stop is a conversation for your prescriber, not me. My job is everything around it.
Proof that strength and habits last
What a jab can't give you is what makes weight loss stick. My clients show what that looks like.
Backed by science
The science backs it up too. The researchers behind that 2025 review of muscle loss with these medicines recommend tailored resistance training to preserve lean mass while losing fat, along with roughly 1.2 to 1.6g of protein per kilo of body weight per day. That's exactly what I do with my clients.
Conclusion
A weight loss jab can give you a head start. What you do with that head start decides whether the results last.
If you want to come out the other side leaner, stronger, and knowing exactly how to keep the weight off, let's talk. Find out more about my GLP-1 support, or book a free consultation.
Ready to lose fat, not muscle? Work with Steve >
