Macro partitioning

Hypocaloric diets cause greater total body weight loss than exercise training, but this weight loss includes skeletal muscle mass reduction, whereas exercise may increase lean body mass.

If you want to lose total pounds quickly, a calorie-restricted diet will be more effective than exercise alone. However, be aware that diet-induced weight loss often includes muscle loss, while exercise can help preserve or even build muscle. For long-term metabolic health, preserving muscle via exercise while managing calories is often a better strategy than rapid weight loss from dieting alone.