Introduction

It’s one of the most popular fitness goals out there: “I want to lose fat and build muscle.” And on the surface, it sounds like a smart and efficient plan. After all, why not kill two birds with one stone?

But here’s the truth: Trying to do both at once is a mistake for most people. While body recomposition (losing fat while gaining muscle) can occur in specific situations, trying to chase both goals simultaneously often leads to frustration, stagnation, and mediocre results.

This guide breaks down the science, the physiology, and the exceptions to the rule—so you can finally take the right path toward your transformation.

1. Physiological Conflict: You’re Sending Mixed Signals

To lose fat, you must be in a calorie deficit—consuming fewer calories than your body burns.
To build muscle, you need a calorie surplus—eating more than your body burns to provide the fuel and resources for growth.

These two goals are inherently conflicting. You can’t be in both states effectively at the same time. When you try, the body lacks a clear directive and progress in either direction is typically slow.

Think of it like trying to drive in two opposite directions—you stay stuck in the middle.

Scientific Backing:

• Hall et al. (2016): Demonstrated impaired lean mass gains in energy-restricted states.
• Phillips & Van Loon (2011): Confirmed that optimal muscle protein synthesis occurs in energy balance or surplus.

2. Your Hormones Won’t Cooperate

Calorie deficits increase cortisol, a catabolic hormone that breaks down tissue (including muscle). At the same time, testosterone and insulin—both anabolic hormones necessary for muscle growth—are suppressed in long-term deficits.

This hormonal state is hostile to muscle gain and recovery, even if you’re training hard.

Scientific Support:

• Tremblay et al. (2003): Chronic energy deficits lead to hormonal imbalances that impede muscle growth.

3. Muscle Protein Balance: The Real Limiting Factor

Muscle growth requires that Muscle Protein Synthesis (MPS) exceeds Muscle Protein Breakdown (MPB). This is known as a positive Net Protein Balance.

In a deficit:

• MPS is reduced
• MPB often rises

The result: It’s incredibly hard to gain muscle unless you’re new to training or significantly overweight.

Scientific Support:

• Phillips & Van Loon (2011): High-protein diets can mitigate muscle loss but rarely support full hypertrophy in a deficit.

4. Body Recomposition: Possible, But Limited

Body recomposition can happen—but only in very specific circumstances:

• Beginners: Untrained individuals respond quickly to resistance training due to neural adaptations and a novel stimulus.
• Detrained Individuals: If you’ve lifted before and taken time off, “muscle memory” allows for rapid regrowth while in a deficit.
• Overweight/Obese Individuals: Excess body fat provides enough stored energy to support muscle growth during fat loss.

Bret Contreras: “Recomping is absolutely possible—but only for beginners, detrained lifters, or those with a high body fat percentage.”

5. Psychological and Practical Downsides

• Progress feels slow: The scale barely moves. Physique changes are subtle.