Lean body mass

Lean body mass Glossary: Lean body mass refers to the part of the body made up of non-fat tissues, mainly muscle but also bone, organs and body water, standing in contrast to fat mass. Lean mass, particularly muscle, plays a key role in mobility, metabolism and general health, and preserving it is important, notably in older animals where muscle wasting can occur, sometimes independently of total weight (WSAVA muscle condition score). This is the counterintuitive part: an animal can be [overweight](/glossary/overweight) yet have insufficient muscle mass, which is why veterinarians use a muscle condition score distinct from the [body condition score](/glossary/body-condition-score). Diet plays a role, with adequate protein in quantity and quality to support lean mass, and physical activity also helps maintain it. During a supervised weight-loss programme, the aim is to reduce fat mass while preserving lean mass, which is why slimming diets are formulated to stay high in protein while limiting energy, helping the animal lose fat rather than valuable muscle tissue. The marker: lean body mass, especially muscle, is what weight management should protect even while shedding fat, linking it to [sarcopenia](/glossary/sarcopenia) in seniors and to the protein-quality discussions throughout the [Petipedia glossary](/glossary).

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