• Emilina Lomas

Can you build muscle and lose fat at the same time?

Perhaps the most debated, most asked fitness question of all time: can you build muscle and lose fat at the same time?




To answer it we have to look at the law of thermodynamics. Thermodynamics is the relationship between heat and energy, in particular how thermal energy is converted to and from other forms of energy, like energy from food. But without getting too deep into the science, we’re going to focus on the first law: that heat is energy, it cannot be created or destroyed, only converted.


In terms of exercise science, assume that if you’re in a caloric deficit (i.e. a negative energy balance), muscle can not be gained because energy can not be created, because of the law of thermodynamics. Furthermore, muscle can only be gained if there is an energy surplus, to allow energy to be converted into muscle.


Seems to make logical sense right?


But it’s not accurate. When we consume calories, your body sends energy to muscle mass and fat mass independently, fueling them both. The assumption, according to broscience is that you need an excess of calories to fuel muscle protein synthesis. But when we look at what is actually needed to build muscle, it’s a bit more complex.


Numerous studies show that to build muscle you need five key things:


  • Water - the majority (65 percent) of our body is water, in a dehydrated state our cells atrophy and we shift into a catabolic state (muscle breakdown).

  • Protein - amino acids are the building blocks of protein, without sufficient protein consumed on a daily basis, we shift into a catabolic state.

  • Glycogen (carbs) and triglycerides (fat) - these two nutrients are non-essential, meaning they can be stored and created by the body.

  • Exercise stimulus - sufficient muscle damage needs to be elicited during training to initiate muscle hypertrophy.

  • Rest - the body needs rest to properly recover from the exercise stimulus to repair and grow damaged muscles.


So now we know how muscle is gained, we can go back to the point in question: can you gain muscle and simultaneously lose fat?


The answer is yes. All five of the mechanisms of muscle protein synthesis can be achieved in a caloric deficit. Sufficient protein can and should be consumed during the cut to ensure muscles are fueled. Carbs and fat will still be consumed during a cut but likely to a lesser extent, however as mentioned, we have ample amounts of glycogen and triglycerides stored in tissues. One pound of body fat equates to 3,500 calories of energy.


In terms of the research, there is a solid amount of evidence to prove it’s possible too. A 12 week study put a group of participants in a caloric deficit, high protein and resistance training schedule. The group lost on average 9.3 pounds of fat and gained 8.8 pounds of muscle mass.


Another similarly laid out study saw the participants lose fat mass and increase muscle mass, again, consuming a high protein diet. A study by the Journal of the International Society of Sports Nutrition studied a group of elite gymnasts who were put on a hypocaloric ketogenic diet for 30 days whilst also continuing professional physical training.


Participants lost on average 2.6 percent body fat and gained 0.9 pounds of muscle mass. These elite athletes were training more than four hours per day and only consuming 22 grams of carbs, and were still able to lose fat and gain muscle mass.


I hope this cleared some things up for you. If you want to build muscle and lose fat simultaneously, ensure you’re eating enough protein, are consistently training at a high enough intensity, drinking water and allowing for proper recovery. Even while in a deficit, if these are followed, you can gain muscle.

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