Building muscle and losing fat at the same time

Building muscle and losing fat at the same time. Is that possible? If so, how can it work if you need a calorie surplus to build muscle and a calorie deficit to lose fat? That actually contradicts "at the same time", doesn't it?

Definition "At the same time"

Let's start from the beginning: "At the same time" means to build muscle and lose fat while being on maintenance calories. We'll get to whether that's possible in a moment by looking at the theory behind it and, of course, the practice. However, let's define "maintenance calories" first.

Maintenance calories

Most people think a constant body weight on a weekly or monthly basis means that we have been on maintenance calories. However, this is not correct. Maintenance calories only means that you take in as many kcal through food as you burn. This does not mean that your body weight has to remain constant. Even if it remains constant, it does not mean that you are on maintenance calories.

Sure, body weight can fluctuate due to temporary water fluctuations. However, we're not talking about that now. These fluctuations even out over several weeks or months anyway. We are talking about a change in body weight due to a changing ratio of muscle to fat mass.

Losing muscle and gaining fat at the same time

Now imagine your body is this energy-storing refrigerator. 1 kg of body fat has about 7,700 kcal and 1 kg of muscle mass has about 1,800 kcal. Let's assume that you have caught a bad flu and have to lie in bed almost all day for 3 weeks.

During this time you will definitely lose some muscle mass. Let's say you lose 1 kg of muscle mass. So your energy storage is reduced by 1,800 kcal. If you eat in a way that you maintain your body weight during the flu, you will have gained 1 kg of fat (the compensation for the 1 kg muscle mass loss). The body fat increased your energy storage by 7,700 kcal. So, in total, you were in a net surplus of 5,900 kcal, WHILE your body weight remained constant.

This is an absolutely realistic example to show that a constant body weight is not a perfect indicator that you were on maintenance calories.

Building muscle and losing fat at the same time

The principle works similarly in the other direction as well. Let's say you start lifting weights and you do it for 3 months. Your body weight remains constant the entire time. As a beginner, you will certainly gain muscle mass during this time. Let's say you built 1 kg of muscle and lost 1 kg of fat. In that example, you weren't on maintenance calories either.

Required energy for building muscle

When it comes to building muscle, the calculation is a bit more complicated. Your body has to expend a relatively large amount of energy for the muscle-building process. Although 1 kg of muscle mass contains 1,800 kcal, your body must spend an additional 4,500 kcal to build this 1 kg of muscle mass. However, it is not yet known precisely how many kcal are required to build muscle.

If we assume this number is about accurate, around 6,300 kcal are required to build 1 kg of muscle mass. If you now build 1 kg of muscle and lose 1 kg of fat, you were in a net deficit of about 1400 kcal over the entire period, ALTHOUGH your body weight remained constant.

Nevertheless, in many cases, a constant body weight is an indicator that you were on maintenance calories indeed – just not always.

First law of thermodynamics

So, as you've already noticed in the last example, there are definitely cases where you can build muscle and lose fat at the same time. Let's take a look at the theory behind this.

Fat and muscle gain require energy and fat and muscle loss release energy. So, for muscle gain you need to be in a calorie surplus and for fat loss you need to be in a calorie deficit.

Simultaneously in a calorie surplus and deficit

Nutrient partitioning

So, to build muscle and lose fat at the same time, you need to be in caloric surplus and deficit at the same time. This sounds unrealistic and is mostly the reason why many people don't believe that you can build muscle and lose fat at the same time. However, this is definitely not a paradox, because muscle and fat tissue must be considered separately.

These are 2 different systems. Your body distributes kcal to muscle and fat tissues independently. This effect is called "Nutrient partitioning" or "Calorie partitioning". So, for example, one tissue type can be in a calorie surplus and the other in a calorie deficit.

For example, if you are in a surplus of 100 kcal, then it is not mandatory that 50 kcal go into fat tissue and 50 kcal into muscle tissue. It can also be that 100 kcal go into muscle tissue and 0 kcal into fat tissue or the other way around. Or - and now it gets interesting - even 200 kcal can go into the muscle tissue. 100 kcal then come from the surplus through food and 100 kcal come from the fat tissue etc.

Calories from food vs. stored in the body

Yes, you have to be in a calorie surplus to build muscle. However, it does not necessarily have to come only from the kcal in food, but can also come from the kcal stored in the body. If you have 20 kg of body fat, you have 154,000 kcal stored in that body fat. You can use this "surplus" for building muscle, even if you eat exactly on maintenance (so no more surplus comes in through food).

This is the reason people with more body fat lose less muscle mass during a diet. They have much more energy stored in their body that can be used. With 20 kg of body fat, you have 154,000 kcal stored in your body, and with only 5 kg of body fat, you have only 38,500 kcal stored. This is a big difference.

Just a little confusing info on the side: If you add the kcal stored in your body to the kcal you consume through food, then you can never be in a deficit - even with the most extreme crash diet. Your kcal needs are always covered by the food and the energy stored in the body.

But sure... if we talk about "calorie deficit", we usually mean that you take in less calories from food than you currently expend. This is how we continue to define deficit/surplus/maintenance - always in terms of calories from food.

Practice

Scientific evidence

That's enough on theory. What does reality show us? Is simultaneous muscle gain and fat loss observed often? Yes! There are countless studies showing this. Before you ask, yes, there are also a lot of studies showing it's even possible in advanced lifters.

A very recent literature review by Barakat et al. (2020) summarizes the results of all these studies. By the way, this literature review does not only show that you can build muscle and lose fat at the same time even as an advanced athlete, it also shows that other factors such as smart and hard training and sleep are much more important than determining the exact amount of calorie intake.

Smart and hard training

And here we are at a very important topic that gets far too little attention from many lifters: Smart and hard training! Without a strong training stimulus, it doesn't matter what or how much you eat. Muscle mass is only built when your body experiences the need to do so. It only experiences this during smart and hard strength training.

Placebo effect

Another important point is the placebo effect. If you want to diet moderately in the next few months and it's already clear to you that you won't be able to build muscle during this time anyway, guess what happens then? That's right, you actually won't build muscle, because you consciously or unconsciously put less effort into your workouts. That's a self-fulfilling prophecy.

However, after reading this article, hopefully, you know that there is no justification at all for this thinking. You can build muscle and lose fat at the same time - even in a non-excessive deficit. Of course, this becomes more difficult when you are very advanced, but it is possible.