Body recomposition, defined as concurrent fat loss and muscle gain, is physiologically possible in trained individuals during a state of energy deficit.

Study: Resistance training as a key strategy for high-quality weight loss in men and women

People who lifted weights while eating fewer calories lost fat and even gained muscle, while those who did cardio or nothing lost muscle too. So yes, you can lose fat and gain muscle at the same time—if you lift weights.

Study: Endocrine, Metabolic, and Skeletal Muscle Proteomic Responses During Energy Deficit With Concomitant Aerobic Exercise in Humans

Even while eating less, the muscles of these men became better at burning fat and less stiff, which means their bodies were getting healthier and more efficient — this shows it’s possible to lose fat and improve muscle function at the same time.

Study: Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial.

Yes, people can lose fat and gain muscle at the same time, even while eating fewer calories — but only if they eat lots of protein and lift weights hard. This study showed that men who ate more protein while dieting and training gained muscle and lost more fat than those who ate less protein.

Study: The impact and utility of very low-calorie diets: the role of exercise and protein in preserving skeletal muscle mass

Even when eating very few calories, people who lift weights can keep their muscle — and with the right conditions, they might even build more muscle while losing fat. So yes, it’s possible to lose fat and gain muscle at the same time.