Mounjaro & Muscle: Staying Strong During the Big Change

So you've started Mounjaro. First off , well done. That's a big decision, and it takes courage to commit to a significant change like this.

I'm Matt, and I work with people at all stages of their fitness journey , including plenty of clients who are using weight-loss medications like Mounjaro, Wegovy, or Ozempic. And there's one conversation I find myself having again and again:

"I'm losing weight, which is great… but I'm worried I'm losing the wrong kind of weight."

That worry? It's completely valid. And the good news is, there's a lot you can do about it.

Let me walk you through what's actually happening in your body right now, why strength training matters more than ever, and how to make sure you come out of this journey stronger , not just lighter.

What's Actually Happening When You Lose Weight on Mounjaro

Here's the thing about Mounjaro (and other GLP-1 or GIP/GLP-1 medications): they work brilliantly at reducing your appetite. You eat less. You feel satisfied sooner. The weight starts coming off.

But here's where it gets tricky.

When you eat significantly fewer calories, your body doesn't just burn fat for fuel. It also starts breaking down muscle tissue , especially if you're not eating enough protein or doing any resistance-based exercise.

Studies suggest that up to 39% of the weight lost on these medications can come from lean muscle mass, not fat. That's a pretty significant chunk.

And this isn't just about how you look (though we'll get to that). Losing muscle affects how you function , your energy levels, your metabolism, your ability to do everyday stuff without feeling knackered.

The "Skinny Fat" Problem

You've probably heard the term "skinny fat" before. It's not the most scientific phrase, but it describes something real: when someone loses a lot of weight but ends up with very little muscle underneath.

The result? You might hit your goal weight on the scales, but your body composition hasn't actually improved that much. You might feel weaker. Clothes might still fit strangely. And your metabolism , the rate at which your body burns calories at rest , has slowed right down because muscle is what keeps it firing.

This is the outcome we want to avoid.

Because here's the frustrating part: research shows that people who stop taking GLP-1 medications often regain about two-thirds of the weight within a year. And when that weight comes back, it tends to come back as fat , not muscle.

So if you've lost muscle during the weight-loss phase, you're left in a worse position than when you started. More fat, less muscle, slower metabolism.

Not ideal.

Why Strength Training Is Your Best Friend Right Now

This is where I get a bit passionate (fair warning).

If you're using Mounjaro or any similar medication, strength training isn't optional , it's essential.

I'm not talking about bodybuilding or spending two hours in the gym six days a week. I'm talking about consistent, resistance-based movement that tells your body: "Hey, we still need this muscle. Don't break it down."

When you do some form of resistance training : whether that's bodyweight exercises, resistance bands, dumbbells, or machines : you're sending a signal to your muscles that they're still needed. Your body responds by preserving them, even when you're in a calorie deficit.

Without that signal? Your body assumes the muscle is spare capacity and starts using it for energy.

What Does "Strength Training" Actually Mean?

It doesn't have to be complicated. Here's what works:

• Bodyweight exercises : squats, lunges, press-ups, glute bridges
• Resistance bands : great for home workouts and travel
• Light dumbbells or kettlebells : even 2-3 sessions a week makes a difference
• Gym machines : perfect if you're newer to training and want guidance on form

The key is consistency over intensity. Three 30-minute sessions per week will do far more for you than one massive gym session followed by two weeks off.

And if you're not sure where to start, that's exactly what I help people with. We can build a simple plan that fits around your life : no complicated routines, no gym intimidation, just movement that works.

Protein: The Other Half of the Equation

Strength training is crucial, but it only works properly if you're giving your body the raw materials it needs to maintain muscle. That means protein.

When you're on Mounjaro, your appetite drops. Which is the point : but it also means you're likely eating less protein than your body needs.

Here's a rough guide: aim for around 1.6 to 2 grams of protein per kilogram of your target body weight each day. So if you're aiming for 70kg, that's roughly 110-140 grams of protein daily.

That might sound like a lot, especially when your appetite is suppressed. But you can get there with some simple swaps:

• Prioritise protein at every meal : eggs, chicken, fish, Greek yoghurt, cottage cheese, tofu
• Add protein snacks : a handful of nuts, some jerky, a protein shake if you're struggling
• Front-load your day : a high-protein breakfast sets you up better than trying to cram it all in at dinner

If you're finding it hard to hit your protein targets, let me know. We can look at your meals together and find easy wins.

What About Muscle Aches and Cramps?

Some people experience muscle cramps or general achiness when they start Mounjaro. If that's you : don't panic. It's usually temporary and tends to settle within 2-4 weeks as your body adjusts.

A few things that help:

• Stay hydrated : aim for 8-10 glasses of water a day
• Watch your electrolytes : magnesium-rich foods (spinach, nuts, seeds) can help
• Gentle stretching : nothing intense, just regular mobility work
• Sleep : your muscles recover while you rest, so don't skimp on this

If you're getting severe muscle pain alongside fever, swelling, redness, or weakness that stops you doing normal activities, get that checked by a doctor. That's not normal adjustment : that needs attention.

This Journey Is About More Than the Scales

I know how tempting it is to obsess over the number on the scales. I get it. But I'd encourage you to measure progress in other ways too:

• How do your clothes fit?
• How do you feel when you climb stairs?
• Can you carry the shopping without getting winded?
• Do you feel stronger, more capable, more energised?

These things matter. And they're directly tied to maintaining : or even building : muscle while you lose fat.

The goal isn't just to weigh less. It's to feel better, move better, and set yourself up for long-term success. That means protecting your muscle mass now, so that when you reach your goal weight, you actually like how you look and feel.

You Don't Have to Figure This Out Alone

Look : Mounjaro is a powerful tool. But it's just that: a tool. It works best when combined with the right movement and nutrition.

If you're currently using Mounjaro (or thinking about it) and you want some guidance on how to train alongside it, I'd love to help. We can put together a simple strength plan that fits your life, your energy levels, and your goals.

No judgement. No pressure. Just practical support from someone who genuinely wants you to succeed.

Get in touch and let's chat about your plan →

You've already taken the first step. Let's make sure the rest of the journey takes you somewhere you actually want to be.