Effect of short-term fasting on lipid kinetics in lean and obese women

We evaluated whole body and regional adipose tissue lipid kinetics and nore pinephrine (NE) spillover during brief fasting in six lean [body mass index (BMI) 21 +/- 1 kg/m(2)] and six upper-body obese (UBO; BMI 36 +/- 1 kg/m(2 )) women. At 14 h of fasting, abdominal adipose tissue glycerol and free fa tty acid (FFA) release rates were lower (P = 0.07), but whole body glycerol and FFA rates of appearance (R-a) were greater (P < 0.05) in obese than in lean subjects. At 22 h of fasting, glycerol and FFA R-a increased less in obese (19.8 +/- 7.0 and 87.1 +/- 30.3 mu mol/min, respectively) than in lea n (44.2 +/- 6.6 and 137.4 +/- 30.4 mu mol/min, respectively; P < 0.05) wome n. The percent increase in glycerol R-a correlated closely with the percent decline in plasma insulin in both groups (r(2) = 0.85; P < 0.05). Whole bo dy NE spillover declined in lean (P < 0.05) but not obese subjects with con tinued fasting, whereas regional adipose tissue NE spillover did not change in either group. We conclude that, compared with lean women, in UBO women 1) basal adipose tissue lipolysis is lower, but whole body lipid kinetics i s higher because of their greater fat mass; 2) the increase in Lipolysis du ring fasting is blunted because of an attenuated decline in circulating ins ulin; and 3) downregulation of whole body sympathetic nervous system activi ty is impaired during fasting.