24-HOUR ENERGY-EXPENDITURE - THE ROLE OF BODY-COMPOSITION, THYROID STATUS, SYMPATHETIC ACTIVITY, AND FAMILY MEMBERSHIP

The present study assessed the possible familial effect in 71 healthy Caucasian siblings on each of the variables determining the inter-indi vidual variations in energy expenditure (EE) measured under standardiz ed conditions. We found that the 24-h EE measured in respiration chamb ers of 71 siblings from 32 different families was positively correlate d with fat-free mass, which explained 82% of the variation between sub jects (P < 0.00001). An additional 10% of the total variation was expl ained by differences in spontaneous physical activity (P < 0.00001), f at mass (P < 0.00001), plasma concentration of free T-3 (P < 0.003), a nd norepinephrine (P < 0.002), whereas plasma values of epinephrine an d androgen hormones did not correlate with 24-h EE. After adjustment f or gender, there was a familial aggregation of both 24-h and sleeping EE, as indicated by intraclass correlation coefficients (r(i)) Of 0.44 (P < 0.02) and 0.58 (P < 0.01), respectively. The familial effect on gender-adjusted 24-h EE was explained mainly by a familial resemblance of fat-free mass (r(i) = 0.48; P < 0.015) and fat mass (r(i) = 0.40; P < 0.03), whereas spontaneous physical activity and plasma concentrat ions of T-3 and norepinephrine did not correlate in families. It is co ncluded that the familial aggregation of EE in Caucasians is mediated mainly through familial resemblance of body composition; even though p lasma concentrations of free T-3 and norepinephrine, independent of bo dy composition, explain an additional proportion of the variation in E E, they do not contribute to the familial correlation.