Can muscles turn into fat?

Monday, May 14, 2007
What kind of shape are you in? Do you have a rippling six-pack or a wobbling keg?

Most us try and stay in good shape but it's easy to be busy, feel tired and let exercise fall to the bottom of the priority pile. So what happens to that hard-earned body if you stop pumping the iron? If you don't move it, will you really lose it?

Michael Slater finds out if muscle can really turn into fat.

The test

We've all seen it, or we think we've seen it. Top athletes or dedicated gym junkies stop training and all the bits that used to be buffed soon look stuffed.

Tony D'Agosto, a former amateur body builder who's given it away, is a case in point: "I was very happy with my body, it was lean, very athletic, it was in good shape, felt really good … the diet was so hard but the look was something I really appreciated. I really enjoyed it."

But then Tony decided that starting a family was his priority and he stopped working out. But his appetite didn't stop: "Pizza was my favourite — I really couldn't wait to get a pizza, I definitely enjoy eating a whole pizza. I'd probably get to the point I'd make myself sick I'd eat that much."

So should we all be worried about this? Could it happen to you?

There's only one way to find out: we've found a bunch of guys who have just come to the end of a hard season with the Sydney Uni Lions rugby league team: Daniel, Murat, Marco and Matt.

"The training and diet is hard to stick to but we're all mates and we go out together so we all know what it's like and keep each other intact," says Matt.

Now, though, their lives will be different. For the next five weeks, we've asked them to do no exercise and personal trainer BJ Linderman will measure the changes.

Michael: Now BJ, given that we're trying to find out whether muscle can turn into fat, these guys are in their off season so I'm expecting them to have a lot of partying, bad diet, boozing and all the rest of it. So how are we going to test that?
BJ: We're going to use a couple of different methods, the first one is the tried and true tape measure, later on we're going to use the bio impedance machine which sends an electronic pulse through their body. It basically gives us pretty good feedback on what their body fat is.

The initial readings are impressive for all the men — but after five weeks of chips and beer will those fat figures be a lot higher?


After five weeks of doing no exercise and eating whatever they like, it's time to see what has happened to our rugby league players' bodies.

BJ is ready to measure their changes: "I expect their body fat levels go up a bit and their lean muscle mass to decrease a bit."

What do the boys think will have happened?

Marco: I think I've put on a lot of fat, don't know if I've kept any muscle but I think we'll find out today
. Murat: Clothes have been getting tighter, especially around the waist — I've been struggling to put jeans on.

BJ takes the same measurements as last time — puts the boys on the scales, then gets them to lie down so the bio-impedance machine can calculate their body fat and muscle mass.

Marco: gained 1.1kg body fat, lost 0.5kgs of muscle.

BJ to Marco: We've got your results here mate, you've put on a little bit of body fat — 1.1 kilos and you've lost about half a kilo of muscle.

Matt: gained 3kgs body fat, lost 0.5kg muscle.

BJ: You went pretty good if putting on body fat was what you were trying to do — you put on about three kilos of body fat and lost about half a kilo of muscle.

Murat: gained 0 kilos of fat, gained 1kg of muscle.

BJ: Okay Murat, got your results. They were a little bit surprising — your body fat has maintained it's levels and your muscle has increased by about a kilo.

Murat hasn't got fatter — he's put on muscle. That wasn't supposed to happen!

BJ: is there anything you need to tell us?
Murat: I'll come clean. I have been working out a bit.
BJ: At least that explains what we got here.

Daniel: lost 2kg body fat, lost 0.7kgs muscle.

So Daniel lost body fat too, plus a bit of muscle mass. But there was a good reason why — a new job.

Daniel: My new job has had a real big impact on the reason I've lost weight — I'm very active in my new job, I walk around a lot.

So the two guys who did what we asked lost muscle and gained fat. But did the muscle turn into fat?

Time to lay this one to rest and Associate Professor Gordon Lynch, an expert in muscle physiology at the University of Melbourne, can give us the answers.

Michael: What about this notion that muscle can turn to fat? Do you go along with that?
Associate Professor Lynch: I completely reject it. Muscle is one type of tissue and fat is a completely other type of tissue.

Here's what Associate Professor Lynch means — muscle can't turn into fat because they're two different things. Muscle is designed to contract, pulling on tendons, which move our bones and give our bodies movement. Fat on the other hand, is the body's way of storing energy. The less energy we use, the more fat we store, ready for when we need it.

So what happens when you stop exercising?

"When we're exercising heavily, we're working our muscles hard, we're eating a lot of food usually to fuel those workouts. If we stop exercising and we're still eating the same amount of food, quite naturally the energy balance between energy in, as food, and energy out, as exercise, or energy expenditure, changes. And so the idea is the balance shifts towards increasing body fat," says Associate Professor Lynch.

So that's it — stop exercising and keep eating as much and on goes the fat. The best solution is to keep exercising because there are benefits to having lean muscle if you want to keep your independence as you get older.

"Regardless of age, you can still maintain muscle mass … to perform the task of daily living we need to have muscle strength," says Associate Professor Lynch.

If you want muscles at 67 or 77 then you'll need to do weights and get protein from vegies, fish and lean meat, and lay off the junk food.

So that's why Tony turned to fat — too much junk food. But he's turned that around and though he'll never be an Arnold Schwarzenegger look-alike again, he's now a personal trainer and keeping his muscle mass up.


So if you don't use it you really will lose it. Your muscles can't turn to fat but you will pile on the pounds if you stop working out.

Fast facts

  • Is it inevitable that we lose muscles and pile on the kilos as we get older? Unfortunately, yes. Our metabolism slows by 10 percent a decade from the age of 20. That creates a decrease in muscle function and because we use them less, muscles begin to waste away. The solution is to eat less and increase your exercise — yes, move it or lose it.

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