Fat-Free Mass Index
The fat-free mass index (FFMI) shows how much lean tissue — muscle, bone and water — you carry relative to your height, like a BMI for your muscle.
Plain English
Patient-Friendly Explanation
The fat-free mass index (FFMI) is a number that shows how much lean tissue — muscle, bone and water — you carry relative to your height. It is like a BMI for your muscle, and it helps doctors see whether weight loss is coming from fat or from precious muscle. Protecting muscle during weight loss keeps your strength and metabolism intact.
Medical
Clinical Definition
FFMI is calculated as fat-free mass (kg) divided by height in metres squared (kg/m²), mirroring BMI but using lean mass. Typical healthy ranges are approximately 17–21 kg/m² in men and 14–17 kg/m² in women; low values suggest sarcopenia, especially below about 17 kg/m² in men and 15 kg/m² in women, though interpretation requires clinical context. During caloric restriction, monitoring FFMI quantifies obligatory lean-mass loss, which resistance training and adequate protein intake attenuate. FFMI is derived from body-composition techniques such as bioelectrical impedance analysis (BIA) or dual-energy X-ray absorptiometry (DXA).
Key Insight
Why It Matters
The scale cannot tell fat from muscle — two people of the same weight can have very different bodies. Our reviews use body-composition readings so we can confirm the weight you are losing is fat, and help you hold on to muscle.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: August 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
