Body fat mass (FM) is the total amount of fat tissue, in kilograms or as a percentage of weight (body fat percentage). It is one of the two main parts of body composition.
The body needs fat (hormones, energy store, protection of organs), but both its amount and its location matter: visceral fat around the internal organs is especially dangerous.
Reference ranges
Approximate share of fat in body weight (the norm depends on age):
| Men — normal | 10 – 20% |
| Women — normal | 18 – 28% |
| Obesity | men > 25%, women > 32% |
| Essential fat | men ~3–5%, women ~10–13% |
What an elevated level means
An excess of fat mass is a risk factor for metabolism and the heart, especially through visceral fat. It is linked to insulin resistance, hypertension, dyslipidemia and chronic inflammation.
Important: an excess of fat also occurs at a normal weight — so-called "hidden obesity", which BMI does not catch.
What a low level means
Too low a fat mass is also harmful. Essential fat is necessary for hormones, bone health and reproduction.
A critically low fat percentage (for example, with harsh diets or eating disorders) leads to hormonal disturbances, in women — to menstrual disruption, reduced bone density and a loss of strength.
How the test is done
Fat mass is assessed by bioimpedance, calipers or more accurately — DEXA. Home smart scales give a rough guide and reflect the trend well.
Look not at a single figure but at the trend and at waist circumference — a simple and reliable indicator of dangerous abdominal fat.
What affects the value
- Calorie balance — an excess is stored as fat.
- Physical activity — reduces fat mass.
- Age and menopause — shift fat toward the abdomen.
- Sleep and stress (cortisol) — promote fat accumulation.
- Hydration — affects the accuracy of bioimpedance.
- Sex — in women the fat share is physiologically higher.
Assess body fat
Assess the percentage and amount of fat mass:
Frequently asked questions
How much body fat is normal?
Roughly 10–20% in men and 18–28% in women; with age the norm is a little higher. It is important not to go to extremes: both an excess and too little fat are harmful to hormones, bones and metabolism.
Can you be “fat” at a normal weight?
Yes, this is "hidden obesity": weight and BMI are normal, but the fat share is high and there is little muscle. Such a body composition raises metabolic risk, so relying on the scale alone is not enough.
Why does not only the percentage but the location of fat matter?
Subcutaneous fat is relatively safe, while visceral fat — around the internal organs — is metabolically active and dangerous: it is more strongly linked to insulin resistance and heart disease. It is indirectly assessed by waist circumference.
Related terms
Sources
- Schutz Y. et al. Fat mass index / fat-free mass index (review). PubMed
- MedlinePlus (NIH) — Body Composition Measurement
- Body fat and metabolic risk (review). NCBI/PMC