Body mass index and serum leptin concentration independently estimate percentage body fat in older adults.

BACKGROUND Because serum concentrations of leptin, a hormone produced by adipocytes, can be relatively reliably and inexpensively measured, it may be considered complementary to, or even a substitute for, body mass index (BMI) as a measure of adiposity. OBJECTIVE We examined the ability of BMI and leptin concentrations, separately and together, to estimate total percentage fat in older adults. DESIGN Total percentage fat measured by dual-energy X-ray absorptiometry and fasting serum leptin concentrations were measured in 2911 well-functioning 70-79-y-old participants (42% black, 51% women) in the Health, Aging, and Body Composition Study. RESULTS Mean (+/-SD) total percentage fat was 29.2 +/-5.0% in men and 40.5 +/- 5.7% in women, and the geometric mean (+/-SD) serum leptin concentration was 5.6 +/- 2.5 ng/mL in the men and 16.4 +/- 2.3 ng/mL in the women. Among men, total percentage fat was strongly associated with both BMI (R(2) = 0.56) and leptin (R(2) = 0.57) in separate linear regression analyses and in a combined linear regression analysis (R(2) = 0.68). Similarly, among women, total percentage fat was associated with both BMI (R(2) = 0.65) and leptin (R(2) = 0.54) separately and in combination (model R(2) = 0.71). Independent relations of BMI and leptin with total percentage fat were also found among both black and white participants. With the population divided into quintiles according to percentage fat, BMI and serum leptin correctly classified 49% of men and 50% of women in the correct quintile. CONCLUSIONS Among older adults, total percentage fat was better estimated by using both serum leptin concentrations and BMI than by using either alone. However, their performance does not suggest that they can substitute for more accurate measures.