Muscle vs Fat – Some Home Truths

I suspect this may be a deeply unpopular post, but what the hey, I didn’t come here to be popular, I came here to be honest (and jacked, and buff, and so on, but I got that side covered).
One of the things I see come up time and time again, on running forums, in exercise groups, weight loss communities, as advice from personal trainers, supposed Health and Fitness magazines and websites, “qualified nutritionists” and even doctors, is a basic misunderstanding about the nature of muscle and fat in your body, and the ways in which we gain and lose both. It is always the same myths being regurgitated and recirculated, so let’s muscle down and chew the fat and deal with them once and for all:

1.) You cannot ‘turn fat into muscle’. By the same token, if you stop working out your muscles will not ‘turn into fat’.

This one does the rounds all the time, particularly on the running groups among new runners.
“I have been running for 8 weeks now and to my horror I have not lost any weight, in fact I have put on 7lbs!”
“Don’t worry, you are building muscle and muscle weighs more than fat.”

or, in discussions on lifting weights and doing resistance training, this gem:
“I wouldn’t want to build muscle, because the moment you stop it will all turn to fat.”

No. Stop it. Fat does not turn into muscle. Muscle does not turn into fat.

Let’s look at an example of some fat and some muscle.

Mmmm, ribeye. Now, put your tongues back in your mouths, and you vegans uncover your eyes. Look at the bits that are fat – they are fat. Look at the bits that are lean meat – they are muscle. Look at what they are actually made up of. By what alchemy do you imagine it is possible to ‘convert’ one into the other?
Muscle tissue is made up of protein fibres, fat is made up of adipocytes, hence the term adipose tissue. There is no way of converting one to the other, as they are different at a molecular level. No amount of exercise, or lack thereof, will make this happen, just as I cannot convert a packet of lard into meat by chucking it around the room a bit, and my nice ribeye steak is not going to be a block of pure fat if I leave it overnight.

I suspect that everyone actually knows this, or would realise this if they stopped to think about it for a moment, and yet this ‘turning fat into muscle’ myth persists, and woe betide anyone who should contradict it.

Interestingly, well to me anyway, the etymology of the word ‘muscle’ comes from the Latin ‘musculus’, meaning ‘little mouse’, possibly because the Romans were out of their gourds on wine and orgies most of the time, and randomly made up names for things, whereas the word ‘fat’ derives from the Old English/Germanic ‘fǣtt’, meaning ‘fat’. Presumably because the Olde English didn’t give a hoot about political correctness and called a spade a spædu and fat, fat.

but back to the main subject, if you can’t turn fat into muscle, how do you get from fat to jacked? Well you can lose the fat and then replace it with new muscle. That works. but leads us onto our next unpalatable truth:

2.) You cannot burn fat and build muscle at the same time.

The simple thing is this: to burn fat you have to be in caloric deficit. Calories in: calories out. That is how it works. To build muscle you have to be in caloric surplus. If all of your calorie intake has been burned up by your daily activity there is nothing left to create new muscle fibres. Calories in: calories out. You cannot be in deficit and in surplus at the same time. That’s just maths.
Your muscles may look and feel bigger after you have burned off a few pounds of fat. That is because the squidgy fat that was coating them has gone and the muscles are actually visible. The muscles themselves have not grown. You can, to an extent, get stronger while burning fat, and you can certainly maintain strength. You can increase endurance while burning fat. You just can’t get bigger and smaller at the same time.

I’m sure there will be disagreement with this and citing of numerous web articles that claim the reverse. I just had a quick Google and found several in well-known fitness magazines, even. Notably all of these articles were accompanied by pictures of models who were clearly using a shit-ton of steroids. So, okay I will concede slightly: if you were to take a cocktail of Tren, Testosterone, Human Growth Hormone and Winstrol, and also work out like a beast and have everything else on point you perhaps could simultaneously gain mass and lose fat for a while. But realistically, that is not something you or I are going to be doing.

3.) Running does not build muscle.

Not 5k, not 10k, not a marathon, not a hundred mile ultra. No matter how far you run, you are not building muscle. If anything your muscles will reduce in size.  If it were true that running distance made your muscles bigger, then marathon and ultra runners would have massively jacked legs. Take a look at Paula Radcliffe or all the Kenyan and Ethiopian marathon elites. Have a look at Kilian Jornet. Are you struck by the huge bulk of their quads? Their calfs like hams?

No, not so much. Distance runners tend to have very slender, wiry physiques. That is not to say they do not have strong leg muscles, obviously, but strength and size are not the same thing. Big muscles would be a great hindrance to an endurance athlete, because the bigger the muscles, the heavier the athlete, and endurance sports are about having a very high power-to-weight ratio.

The exercises people who build their leg muscles do are things like squats, leg presses, deadlifts and so on, using heavy weights, whilst eating really large amounts of food.

What this unfortunately means is, if you are exercising to lose weight, and you are just doing cardio, and have seen an increase in scale weight, then it is not muscle you have put on. It could be water weight if you have just started, but if you are progressively increasing in weight, then it is because you are gaining fat, and the reason that is happening is because you are in caloric surplus. You are eating too much. This may be disheartening to hear, but if you understand what the problem is you can do something about fixing it. If you comfort yourself (or others) with the old ‘fat turning to muscle’ myth, then you are simply just lying to yourself, and you are not going to achieve your goals. If you are doing a lot of cardio and gaining weight, then go back to your TDEE calculator and do the maths again, Make sure you have your maintenance calorie intake correct. Make sure you have calculated what deficit you are aiming for correctly. Then look carefully at your calorie tracker. Are you recording your daily food intake correctly? Some calorie trackers can be a rather blunt tool. My Fitness Pal is generally pretty good but you can get significant errors which result in underestimating your calorie totals. If you are not tracking calories and do not know your daily target and deficit. well, that is probably going to be the answer, right there, rather than some fat to muscle magical hocus pocus.

Typically whenever this point is made in a forum (usually a little more diplomatically than I have been here, but hey, this is my blog and I will be as blunt as I feel necessary), there is a flurry of retorts, invariably along the same lines, so, lastly…

4.) Yes, we are ‘all different’. Some of us like opera and some of us don’t, some of us like running and some of us don’t; some of ‘them’ like Marmite, and we don’t, but in many other, really essential ways we are all the same. Basic biochemistry being one of the latter. Indeed we do “all have our own opinions and are entitled to them”, but metabolism is not a matter of opinion, it is a matter of fact. If you are serious about losing bodyfat, or building muscle, you are going to have to deal with facts rather than opinion in order to achieve success.


  1. Julia Holman

    Yes this makes sense. As a runner I always thought I was growing muscles as my legs were firmer and stronger, but now I see I was losing fat and perhaps using the ones I do have more effectively? I do think alot of the debate stems from wanting to look better, or become the ultimate image we have of ourselves. I am not really fussed what the science is but if something takes me closer to my body / running achievement goal then great. For example I will be starting dry brushing on my thighs and bum as it has been proven to reduce the visibility of cellulite ( the vigorous brushing just moves it around I am guessing). As for calories, I would prefer to get my teeth around that tasty steak than the latest offering from M and S- the cauliflower steak for £2.50….. WTF is all this coming to.

  2. Abi

    Nicely put!

    But gosh it can be hard to convince people that they aren’t losing weight because they eat too much. Or in fact that they aren’t gaining weight because they eat too little, for that matter. People. 🙂

    Just a thought, but have you ever noticed how, when the bicep is working it kind of looks like a little mouse is running up and down the arm under the skin? Or is that just me? Or is that just gross?

    1. Post
      Billy Rhomboid

      I think the little mouse in the bicep thing may in fact be what the Romans were alluding to, rather than it just being a drunken whimsy on their part.
      I confess I was one of those ‘eats too little and still expects gainz’ people. In fact I was one of those ‘2 hours of cardio and HIIT a day on 1400 calories and wondering why I wasn’t gaining muscle’ people. But now those days are gone and I’m all about ALL THE FOODS

      1. Abi

        What did the Romans ever do for us, eh? I used to like seeing that bicep move up and down, now I’m not so sure 🙂

        I’m very interested in the difference between muscular mass gain and strength gain, I’d not really thought about it before – so thanks for that anyway!

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