But first a disclaimer: this article is purely about body composition (the amount of body fat and muscle in the body) and how to change body composition. This isn’t about health, or fitness, or strength even. We also don’t dictate goals to you, it’s your body and your rules. If you are interested in lowering body fat and building muscle then please read on.

The short answer is no, but let’s break it down and explain why the human body doesn’t work like that and where these ideas come from.

I’m going to ramble on a bit but I promise there is some practical advice for you to follow, and hopefully you will understand how to affect your body composition much more after reading. 

Can you turn fat into muscle?

There isn’t a mechanism in the human body for this to happen.  Fat cannot directly be turned into muscle.  Only amino acids (protein) can be turned into muscle and furthermore for most people this doesn’t happen particularly effectively, unless carbohydrates are present.  Low levels of dietary fat can however make building muscle harder and if this is combined with having a low bodyfat percentage, even more so. This is where the myth comes from.

Like a lot of myths in the fitness industry, it comes from the world of professional bodybuilding circa 1980s.  If you watch a professional bodybuilder’s body transformation (especially back then) they tend to go from very lean, to slightly chubby and then to very muscular and lean again.  They do not however convert the bodyfat into muscle, in fact they gain the fat whilst building the muscle and reveal the newly gained muscle as they lose the fat.  The reason for this is that to build muscle it’s best to be in a calorie surplus.  In fact, for most people it’s essential. 

In scientific studies around skeletal muscle hypertrophy (building muscle) people are usually divided into 3 hypertrophic groups: non responders, moderate responders, and hyper responders.  As with all things in the human body it is much more complex than that, there are many mechanisms in the human body that contribute towards hypertrophy, not limited to: androgens (like testosterone, and human growth hormone), endogenous inhibitors, osteocalcin, and plasma membrane mechanosensors (these are the ones that become more active after weight training). These are active to differing levels in people and they make up the genetic component of muscle building.  Hyper responders are 4-5 times better at building muscle. 

Insulin can be your trump card though (assuming you aren’t going to take anabolic steroids).  Spiking your insulin through diet, along with negating the muscle wasting effects of being on a low calorie diet (or low carb or low fat diet) should lead to a significant amount of muscle growth (assuming adequate rest etc is also happening). 

Unless you are a ‘hypertrophic hyper responder’ (yes this is a real term) it is unlikely that you are going to build a significant amount of muscle whilst following a reduced calorie diet. 

Being in a calorie surplus will also mean that you gain some body fat too.  How much muscle and how much body fat you gain will depend again on many factors (some of which you can affect): hormone profile (influenced heavily by age, bodyfat percentage, starting muscle mass, and gender), training routine, rest and recovery, exact amount of the calorie surplus, and macronutrient breakdown (percentage of fat, protein and carbohydrates). 

Losing the fat without losing muscle

Toning is just fat loss really.  A toned body is a description reserved for a body or body part that has low levels of body fat along with visible muscle.  There is no real difference between toning a body part and losing fat from it, apart from the fact that getting a toned composition is harder than starting your fat loss journey.  In other words the last 10lbs of weight loss is harder than the first 10lbs. 

Losing the fat/toning without losing the muscle

When you are losing weight you can’t decide whether you lose fat or muscle just by wishing it to happen. However the more body fat you have the more likely it will be that you lose fat ahead of losing muscle mass.  Just like when building muscle, losing fat is a multivariate experience.  With respect to many of the hormonal factors the same hormones that help with muscle building also help with retaining muscle.  We’ve spoken about these factors in enough depth. 

Let’s look at things you can control in terms of maximising the fat loss/toning section of your journey. 

Unless you are in the hypertrophic hyper responder category mentioned above it is very likely that you will lose some muscle mass along with the body fat.  Just like the muscle building phase, the key is to preserve muscle mass whilst maximising the amount of body fat you lose.   The biggest factors that will affect how much body fat you lose vs muscle will be: starting body fat percentage, calorie deficit, macronutrient breakdown down, weight training (not over or under training), genetics, stress, rest and recovery. 


What it all actually means.  If you want to gain muscle and lose fat it’s best to do one and then the other.  You will gain some fat when you build muscle and you will lose some muscle when you lose fat.  Your body also builds muscle best if your body fat isn’t too high and isn’t too low, because this sweet spot tends to lead to a beneficial hormone profile.  As a guide if your body fat is above 20% for men and 25% for women you might be best starting with a fat loss routine, and if it’s lower than that then you might be best starting with a muscle building routine.  After that, slow and steady wins the race. 

For muscle building try upping your calorie intake by 400kcals and see what happens on the scale.  This can easily be done by adding a large snack and maybe a protein shake if you are struggling to hit a good total protein figure.  You also want to have enough protein in your diet to provide the amino acids to allow your body to build muscle. 1.5-2g per kg of lean bodyweight tends to be the number here, with the rest of your calories coming from a mixture of fats and protein (probably in a 2-1 ratio of carbs to fat but this is a bit more subjective).

Similarly to lose fat and maintain muscle mass a slower approach is best.  A 400kcal deficit should do the trick.  Protein demands for maintenance of muscle mass as much less.  You might only need a gram per kg of bodyweight as long as you don’t drop your calories too low so that your body needs to break down dietary protein for fuel. 

To build muscle you want to train your body pretty hard 3-5 times a week, although you should still get some results with twice a week (especially if you are relatively new to weight training). 

To lose fat then you need to back off the intensity just slightly.  You can still train 3-5 times a week but be aware that your ability to recover is impaired.  So maybe drop the last set or 2.  Walking and other lower intensity activities will be your friend here too.  Take that 10000 step a day guideline seriously!

Hopefully that explains some body composition training and diet myths and gives you the nuts and bolts of what you would need to do to change your own body composition. 

In my next posts I’m going to go into greater detail on how to gain muscle and how to maintain muscle whilst losing fat.