Energy balance myths: Why you can gain fat in a deficit

Categories: Articles, Nutrition

In my previous article I debunked the myth that you can’t lose fat and build muscle at the same time. You can and most people should. And that’s not the only major misconception surrounding thermodynamics and the energy balance principle.


Myth: Energy balance dictates weight change

If you are in negative energy balance, your body will burn some of its own energy. If you are in positive energy balance, your body will store energy. These are irrefutable conclusions that logically follow from the laws of physics, specifically the first law of thermodynamics.


As a result, being in an energy deficit equals weight loss and being in an energy surplus equals weight gain, right? No doubt you’ll have seen an image like the one below.


Energy balance


In fact, the following image, which is basically the same as the above image but uglier, appears in the respectable journal of Nutrition Reviews from Oxford University Press, the largest in the world.


Energy balance Schoeller 2009


Yet it’s wrong to equate energy balance with weight change. Within the context of a sedentary individual on a balanced diet that only changes his or her energy intake, it is generally correct. However, as a law, which is how most people perceive it, it is false.


The logical error is that not all bodily mass corresponds with stored energy. There are many ways to change your weight while remaining in energy balance.

  • When you go on a ketogenic maintenance diet, you will almost certainly lose body mass without being in a deficit. The lost bodyweight will mostly be water as a result of the lower carbohydrate content of your diet and changes in your body’s electrolyte balance.
  • Foods that cause abdominal bloating and water retention can similarly cause weight gain without a caloric surplus.
  • Not to mention diuretics, the menstrual cycle, drugs, changes in mineral consumption, colon cleanings, creatine, etc.

There are many ways to change your weight long term without changing your body’s amount of stored energy.


Moreover, you can be weight stable while being in a deficit. In my article on the myth that you can’t lose fat and build muscle at the same time, I showed evidence of complete body recomposition in a client and in many scientific studies. You can gain muscle (technically lean body mass, but that’s what most people mean when they say ‘gain muscle’) just as fast as you’re losing fat and a a result your weight will remain the same. This invalidates the idea that energy balance dictates weight change, since evidently being weight stable does not mean you are in energy balance. And being in a deficit does not mean you will lose weight.


And yes, that means the test of finding your ‘maintenance calories’ by seeing at which caloric intake you remain weight stable for 1-2 weeks is not universally correct. I’ve had some clients achieve nearly perfect body recomposition during contest prep. Obviously, their contest prep caloric intake wasn’t their maintenance intake.


And it gets better.


Truth: You can gain weight in a deficit

In true spirit of bodybuilding nihilism, I received the following comment on this site when I explained earlier that energy balance does not dictate weight change.


Nihilism cant gain 3 lb of muscle lose 1 lb of fat


Challenge accepted. In fact, how about we double the odds? Say 6 pounds of lean body mass gain while losing 2 pounds of fat? Ok, you’re on.


Here’s the DXA scan progress of one of my clients. Note how he gained 6.2 lb of muscle while losing 2.1 lb of fat in under a month. Here‘s the full anonymized DXA scan report of his progression.


DXA weight gain in deficit


Don’t believe my data? In my debate about protein requirements in a deficit with Eric Helms, I brought up the Maltais et al. study that showed no difference in body composition changes between protein intakes of 1.1 – 2.1 g/kg. In this study, one group lost 1.1 kg of fat while gaining 1.7 kg of lean body mass. Another group lost 0.9 kg of fat while gaining 1.4 kg of muscle. In other words, both groups gained lean body mass (‘muscle’, as people generally use the term in this context) faster than they lost fat. And these were elderly geezers.


And it gets better still.


Truth: You can lose fat in a surplus

“If someone gained more muscle than he lost fat, he gained weight and thus he was in a caloric surplus by definition.” This was the objection I received from several people when I tried to explain the above earlier. As we saw above, however, this is based on the flawed assumption that energy balance dictates weight change.


This isn’t just a semantic argument where people just have different definitions. The energy balance equation is a mathematical principle.


Change in body energy = Energy intake – energy expenditure


With the metabolizable energy densities of fat and lean body mass from Hall (2008) we can precisely calculate the deficit or surplus someone was in based on that person’s body composition change. Someone who gained 3 pounds of muscle and lost 1 pound of fat must have been in a net energy deficit of 1810 kcal. This is physics, not an opinion.


Taking this a step further, you can lose fat in a surplus. Fat loss occurs during a surplus when you gain muscle fast enough to offset the energy your body receives from the fat loss.


The caveat is that based on Hall’s calculations you have to gain muscle at a rate 5.2 times as high as your rate of fat loss. In other words, you have to gain 5.2 pounds of muscle for every pound of fat you lose. This is uncommon to the point that I used to say the body would simply not let this occur in a natural lifter. I have also never seen this occur in research in a situation where fat loss was significant.


However, based on an analysis of my own client data, I have to correct myself. It is possible to lose fat in a surplus for a natural lifter. For example, here’s the DXA progression report of one of my female clients. We only started working together in the last period of this report, so you can ignore the bottom 2 rows. In our coaching period, she lost 1.3 pounds of fat while gaining 6.8 pounds of lean body mass. That just puts her in positive energy balance during this period by 170 calories (kcal). Here is the full DXA documentation of her progression.


3 kg muscle gain in deficit


Truth: You can gain fat in a deficit

Following the same logic, you can also gain fat in a deficit. If you lose muscle 5.2 times as fast as you get fat, you gain fat while remaining in a deficit. Unless your weight loss program really sucks though, I should hope this only ever occurs if you stop training, you have a serious medical condition or there are drugs involved.



Energy balance and weight change are almost wholly distinct from each other.

  • Your weight can change without any change in bodily energy storage due to changes in water weight and mass in your digestive tract.
  • You can be weight stable yet be in a deficit. So you can gain muscle and lose fat at the same time.
  • If you’re gaining weight, you may still be in a deficit, because you can gain muscle faster than you lose fat.
  • If you’re losing weight, you may still be in a surplus if you lose a lot of muscle mass.
  • You can lose fat in a surplus if you rapidly gain muscle.
  • You can gain fat in a deficit if you rapidly lose muscle mass.


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About the author

Menno Henselmans

Formerly a business consultant, I've traded my company car to follow my passion in strength training. I'm now an online physique coach, scientist and international public speaker with the mission to help serious trainees master their physique.

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