On Ozempic or Mounjaro? Lose the Fat. Keep the Engine.

Im on Ozempic or Mounjaro. Do I need to train differently?"

I get asked this a lot now. On the gym floor, in DMs, from clients who quietly mention it halfway through a set.

So if you're on a weight loss medication, this one's for you.

No judgement. You're far from alone. A UNSW study published this year estimates about half a million Australians use GLP-1 medicines regularly, and private prescriptions have exploded since 2020.

These drugs work. They quiet the food noise, and the scale moves.

But there's a part of the story most people aren't told when they get the script. And it matters more the older you are.

What these drugs actually do

Ozempic and Wegovy (semaglutide) and Mounjaro (tirzepatide) mimic gut hormones that tell your brain you're full. Your appetite drops. Digestion slows. You eat less without white-knuckling it.

That's the whole trick. A big, sustained calorie deficit, made easier.

Which is great for fat loss. The problem is your body doesn't only pull from fat when you're in a big deficit. It pulls from whatever it decides it can spare.

And if you're not using your muscle, your body decides it can spare a lot of it.

The part nobody mentions at the pharmacy

In the big clinical trials, a sizeable chunk of the weight people lost wasn't fat.n the big clinical trials, a sizeable chunk of the weight people lost wasn't fat

Trial	Drug	Share of weight lost that was lean mass
STEP 1 (body composition substudy)	Semaglutide (Ozempic, Wegovy)	About 40%
SURMOUNT-1 (body composition substudy)	Tirzepatide (Mounjaro)	About 25%

So roughly a quarter to two-fifths of the weight that came off was lean tissue. Source

Now, let's be honest about what that number means, because the internet loves to scare people with it.

"Lean mass" isn't all muscle. It includes water, organs and other tissue. So these figures are the worst case, not a pure muscle count.

And losing some lean tissue happens with any serious weight loss. Diet alone typically costs you 20 to 30% lean tissue too. Fat still comes off faster, so most people end up with a better ratio of muscle to fat than when they started.

So no, the drug isn't secretly melting you.

But "normal" isn't the same as "fine." Especially if you're over 40, when you're already losing muscle every year just by getting older. Stack a big drug-assisted deficit on top of that and you can lose muscle you will work very hard to get back.

There's also early data suggesting the people at most risk are the ones who are already less mobile. One large real-world analysis (not yet peer reviewed) found people with joint pain like knee or neck pain tended to lose more lean mass.

The less you move, the more your body treats muscle as optional.

Why you should care about the muscle

Muscle isn't vanity. It's the engine.

It's what gets you up off the floor, carries the shopping, lifts your kid, and keeps your knees and back from doing all the work. Lose too much and you get weaker. Everyday things start feeling harder.

It's also one of the biggest drivers of how much energy you burn just existing. Less muscle means a smaller engine, which makes keeping the weight off harder.

And here's the uncomfortable bit. Many people don't stay on these medications forever. If you come off them with less muscle than you started with, the appetite comes back but the engine doesn't. That's a recipe for regaining fat, not muscle.

You can end up lighter on the scale and weaker in real life.

That's not the trade anyone signed up for.

The fix isn't complicated

You don't need a special "GLP-1 workout." You need the same things that protect muscle in any fat-loss phase. You just can't afford to skip them.

1. Lift weights. Two or three times a week.

This is the big one. Resistance training is the signal that tells your body this muscle is being used, so don't break it down.

A report from Les Mills and ukactive recommends strength training two to three times a week for people on these medications. Full-body sessions built around the big movements: squat, hinge, push, pull, carry.

And it has to get progressively harder over time. More weight, more reps, better control. Waving pink dumbbells around while scrolling doesn't count.

Start early, too. Don't wait until you've lost 15 kilos to decide you want to keep your muscle.

2. Prioritise protein at every meal, even when you're not hungry.

This is where the medication works against you. When your appetite disappears, protein is usually the first thing to go. A few bites of toast and you're done.

So flip the order. Eat your protein first, before your appetite shuts the shop. Aim for a solid serve at each meal, roughly 25 to 40 grams for most people, rather than one big hit at dinner.

Greek yoghurt, eggs, fish, chicken, tofu, a shake if you have to.

Your daily target depends on your size, kidneys and medical history, so get your GP or a dietitian to set the number.

3. Measure body composition, not just the scale.

The scale can't tell you what you lost. It just tells you that you lost.

Get a body composition scan (DEXA or InBody) at the start and every few months. Track your strength numbers in the gym. Watch how your clothes fit. If the scale is dropping and your lifts are going backwards, that's your early warning.

4. Fuel and hydrate around training.

Training completely empty on these drugs is a fast way to feel dizzy and flat. Have something small and protein-rich an hour or so before, drink plenty of water, and back off the intensity on days the nausea is bad. Consistency beats heroics.

Your doctor's job vs your job

Let's be clear about the lines here.

Your doctor manages the medication. The dose, the side effects, whether it's right for you. That's not my lane and it's not yours to freelance on. Talk to them before you start a new training program, especially if you've got heart, joint or blood pressure issues.

Your job is everything the medication can't do for you.

The drug can turn down your appetite. It can't lift the weight. It can't eat the protein. It can't build the habits you'll need on the day you stop taking it.

That part's on you. And on whoever's coaching you.

The bottom line

The medication helps you lose weight.

Lifting decides what kind of weight you lose.

Lift two or three times a week.

Eat your protein first.

Measure what matters.

Lose the fat. Keep the engine.

Message me if you want a strength plan built around your medication.