How to lose fat and gain muscle simultaneously

Losing fat and gaining muscle simultaneously (body recomposition) requires a coordinated approach to nutrition and resistance training. This article outlines practical, evidence-based strategies to achieve both goals together.

This article is from the Bodyweight section of our Library.

Articles in this series:

Article 1: What Is Body Recomposition?
Article 2: Training for Body Recomposition
Article 3: Nutrition for Body Recomposition
Article 4: Rest and Recovery for Body Recomposition

When most people think about changing their bodies, they’ll focus on the number on the scale. But that single number obscures something far more important: what your body is actually made of.

Body recomposition, which involves simultaneously reducing fat and increasing muscle represents a different approach to defining what constitutes a “healthy” physical change. Rather than simply making your body smaller, body “recomposition” focuses on improving what your body is made of.

This article is part of a four-part series on body recomposition — the process of losing fat while maintaining or building muscle. Across the series, we cover what recomposition is and how it comes about, the role of resistance training, nutrition, and rest. Each article builds on the previous one to provide a complete overview, so please read away!

Beyond Body Weight: Body Composition

Your total body weight consists of many different parts: fat mass, skeletal muscle, organs, bones, nerves, water, and connective tissue, to name a few.

When you step on scale, you're measuring all of these components together. Whereas body composition refers to how “much” of these different tissues you have, usually their relative proportions to each other (or sometimes your relative to your height).

The most commonly used body composition measure is the ratio of fat you have relative to your fat-free mass (i.e., muscle, bone, and other non-fat tissues). But many others are used as well.

The distinction between body weight and body composition is significant. Two people of the same height and weight can look completely different and have vastly different health profiles depending on their body composition.

The person with more muscle mass and less fat tissue generally has better health prospects, greater functional capacity, and lower disease risk — even if they weigh the same as someone with more fat and less muscle.

A Contradiction

For years, conventional wisdom has suggested that building muscle and losing fat are mutually exclusive.

The reasoning seemed logical: building new tissue (any type) requires excess energy (a calorie surplus), whilst burning fat requires an energy deficit. How could you possibly do both at once?

This apparent contradiction comes from viewing the body as a single, unified system with one energy system responsible for supplying and regulating all tissues in the exact same way.

In reality, muscle tissue and fat tissue are independently regulated and respond to different things. If this were false, you would simply not be able to grow muscle in an energy deficit [1].

Muscle Tissue vs. Fat Tissue

Fat tissue (adipose tissue) and muscle tissue are not simply passive storage depots. Both are metabolically active, independent organs with their own hardwired regulatory systems.

Fat tissue stores energy primarily as triglycerides and releases them when energy is needed. Whereas muscle tissue is composed of proteins that contract to produce force and movement.

These tissues respond to different hormonal signals and operate on different timescales. For example, fat breakdown can occur very quickly when energy is needed.

Whereas, building muscle is slower and requires specific “stimuli” and conditions for it to grow, and, unlike fat, not dependent on the amount of energy available.

This independence means that, under the right conditions, you can break down fat for energy while at the same time stimulating muscle growth.

Protein: a structural requirement

Here's a crucial point: whilst energy (or “calories”) and building materials (“dietary proteins”) are both necessary for life, they serve fundamentally different purposes.

Your body can use fat, carbohydrate, or protein for energy, but only protein provides the material required to build new muscle tissue [2].

Think of it this way: calories are like fuel, whilst protein is like bricks. To build a house (muscle), you need bricks, not just fuel for the builders.

Your body cannot make muscle proteins from fat or carbohydrate — they can only come from dietary protein. This is why adequate protein intake is essential for body recomposition, even when total calories are lowered to promote fat loss.

When protein intake is sufficient during an energy deficit, your body can maintain or even increase the rate at which it builds new muscle [3]. It can do this while breaking down stored fat to provide energy needs (which includes building muscle itself).

The Energy Deficit

An energy deficit is better understood as a boundary condition rather than an on-off switch. When you consume fewer calories than you expend, you've created a situation where your body must access stored energy to keep it going.

But this doesn't automatically mean you’ll start breaking down more of your muscle to use for energy.

Your body has a choice between two major energy reserves: your fat tissue and the protein in your muscle tissue.

Which one it chooses to increase the breakdown of depends on several factors, like how large the deficit is, your energy needs, hormones, your physical activity level, and the availability of other nutrients.

Moderate energy deficits combined with resistance training and an adequate supply of dietary protein can lead to the body preferentially using fat for energy while maintaining (or even building) muscle [4].

“Energy Partitioning”: Where Does It All Go?

The concept that ties this all together is energy or nutrient partitioning, where your body decides to send incoming energy and nutrients to.

Will they be metabolised for energy straightaway? Will they be stored? In your liver, fat tissue, muscle or elsewhere? Or should they be used to build new tissue? If so, what tissue? Liver tissue, fat, muscle tissue or something else?

The answer to these questions is determined by a combination of factors, including your hormones, genetics, environment, and other lifestyle choices.

When you combine resistance training with an adequate supply of dietary protein and a (moderate) calorie deficit, you are essentially instructing your body to send nutrients towards your muscles (for maintenance and growth). You are also asking stored fat to be broken down and used for energy.

Who Can Achieve Body Recomposition?

The potential for body recomposition isn't uniform across all people or circumstances. Those who are new to exercise and resistance training will likely have greater room to increase their muscle mass (in relative terms).

Likewise, those who have larger amounts of body fat have greater potential to change their body composition.

Age and health status will also likely affect the amount of “recomposition” you can achieve. However, this does not mean that those who are older, leaner, have certain diseases, have more muscle or are already well-trained can’t achieve body recomposition — because they can [5].

However, although still possible, there is probably a point where it becomes more “efficient” (i.e., quicker, easier and/or better results) to dedicate specific periods to building muscle (in an energy surplus) or reducing fat (in an energy deficit) than trying to achieve both at the same time.

Some people may also just want to focus primarily on one component recomposition. For example, you may want to build a lot of muscle while losing only a little fat, or you may want to lose a lot of fat while maintaining (rather than gaining) muscle. You’ll need a specific plan for that.

What’s Next

Fat loss and muscle gain aren't in opposition with one another; they are controlled by separate processes that respond to separate biological signals. Sure, there are overlapping factors that may affect both processes. However, the key is to tip the biological conditions in your favour if body recomposition is your overall aim.

In the next few posts in this series, we’ll discuss how to create these favourable conditions. What specific signals trigger these changes? How much protein, what type of exercise, and what degree of energy deficit are required for the recomposition process?

3 Quick Questions

Q: Can I build muscle and lose fat at the same rate?

You can build muscle and lose fat at the same time, but not necessarily at the same rate (or speed). Technically, you could change both tissues at the same rate, but because they’re controlled by independent processes and influenced by different factors, most people tend to be able to lose fat a lot quicker than they can gain muscle.

Q: Is body recomposition only possible for beginners?

No, but because the magnitude of change is typically largest for training novices or those who are already carrying a lot of fat. Leaner, well-trained people can still achieve recomposition, but the changes will probably be more modest. There could still be room to improve your training and nutrition.

Q: If the scale doesn't move much, am I making progress?

Possibly, yes. If you're gaining muscle whilst losing fat in roughly equal amounts, your total body weight might change less than expected, but your body composition will improve significantly. There are more important things than scale weight. We’ve written a separate article on it.

Sources

1. Areta JL et al. Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit. Am J Physiol Endocrinol Metab. 2014 Apr 15;306(8):E989-97. PMID: 24595305

2. Tipton KD, Wolfe RR. Exercise, protein metabolism, and muscle growth. Int J Sport Nutr Exerc Metab. 2001 Mar;11(1):109-32. PMID: 11255140.

3. Pasiakos SM et al. Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. FASEB J. 2013 Sep;27(9):3837-47. PMID: 23739654

4. Garthe I et al. Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. Int J Sport Nutr Exerc Metab. 2011 Apr;21(2):97-104. PMID: 21558571

5. Bonilla DA et al. Editorial: New insights and advances in body recomposition. Front Nutr. 2024 Sep 3;11:1467406. PMID: 39290563