What is Lean body mass?

Lean body mass is your total body weight minus the weight of your body fat. It includes muscles, bones, organs, skin and body water. When people talk about keeping lean mass, they usually mean holding on to muscle while losing fat.

It matters because muscle takes more energy to maintain than fat and supports strength and everyday movement. For example, someone weighing 70 kg with 20 percent body fat has about 56 kg of lean body mass. Body fat estimates from home scales are rough, so use them only to spot trends.