Expressing fat-free mass (FFM) and body fat mass (BFM) as percentages of body weight or by weight is unsatisfactory. 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 use of height-normalized indices, namely, a FFM index [FFM (kg)/height (m)2, or FFMI] and a BFM index [BFM (kg)/height (m)2, or BFMI]. We calculated these indices in a reference population of 124 healthy young men and in 32 nonobese young men (from the Minnesota Study) before, during, and after experimental semistarvation. When values for FFMI and BFMI falling 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 Minnesota Study subjects after 12 wk of semi-starvation. These findings indicate that FFMI and BFMI may be useful in nutritional assessment.

Resting metabolic rate (RMR) was measured in 154 women and 48 men before the beginning of a weight reduction program. In both sexes there were significant univariate correlations between RMR and fat-free mass, body fat, weight, fat cell weight, and fat cell number (from total body water). Women also showed significant correlations between RMR and fat cell number (from total body potassium), free triiodothyronine index, and fasting and postglucose insulin levels. Multiple regression analysis showed that both fat-free mass and fat cell weight and number were significant predictors of RMR. The contribution of fat-free mass was three to five times greater per kg than that of body fat. There was no significant contribution of thyroid hormones or insulin to the prediction of RMR. Fat cell number and fat cell weight were significant predictors of RMR, whether determined from body water, body potassium, or a formula using both water and potassium. There was no significant difference in regression coefficients between men and women. Thus the difference in RMR between the sexes is probably caused by the higher proportion of fat-free mass in men. The effect of age was small and not statistically significant.

This study was designed to identify psychological, behavioral, and physiological correlates of short- and long-term weight loss. Measures of psychological functioning, body composition, fat cell size and number, and attendance were evaluated in 76 obese women for their relationship to weight loss at the end of treatment and at a 1-y follow-up evaluation. Losing more weight during the first month of treatment and attending a higher percentage of treatment sessions were strongly associated with greater weight loss at the end of treatment and at 1-y follow-up. In addition, patients with the highest initial weights lost the most weight both at the end of treatment and at 1-y follow-up. Easily obtained measures are as successful in predicting weight loss as are more expensive and complicated measures.