Body composition

Fat-free Mass Index

Expressing fat-free mass (FFM) and body fat mass (BFM) as percentages of body weight is unsatisfactory. By expressing it as an index of height, they are more useful. For example, tall patients with protein-energy malnutrition (PEM) can exhibit values for FFM and BFM similar to those of shorter well-nourished individuals. To obviate such difficulties, we propose the use of height-normalized indices, namely, a FFM index (FFMI) and a BFM index  (or BFMI).

The formulas are:
  •  FFM index: FFM (kg)/ length (m)²
  • BFM index: BFM (kg)/ length (m)² 

Background: Minnesota Study

We calculated these indices in a reference population of 124 healthy young men and in 32 non-obese young men (from the Minnesota Study) before, during, and after experimental semi-starvation. FFMI and BFMI values below the reference cohort's 5th percentile cutoff point,  were used as a criterion for PEM. These indices, together with basal oxygen-consumption rate, diagnosed PEM in 27 of the 32 subjects after 12 weeks of semi-starvation. These findings indicate that FFMI and BFMI may be useful in a nutritional assessment. Read more in the article 'Height-normalized indices of the body’s fat-free mass and fat mass: potentially useful indicators of nutritional status' by Vanltaiie, Yang, Heymsfield, Funk and Boileau (1990).