Storage Rates of Circulating Free Fatty Acid Into Adipose Tissue During Eating or Walking in Humans

We measured subcutaneous adipose tissue free fatty acid (FFA) storage rates in postprandial and walking conditions to better understand the contributions of this pathway to body fat distribution. Palmitate tracers were infused intravenously and fat biopsies collected to measure palmitate storage in upper- (UBSQ) and lower-body subcutaneous (LBSQ) fat in 41 (17 men) and 40 (16 men) volunteers under postprandial and under postabsorptive walking conditions, respectively. Postprandial palmitate storage was greater in women than men in UBSQ (0.50 ± 0.25 vs. 0.33 ± 0.37 μmol ⋅ kg fat⁻¹ ⋅ min⁻¹; P = 0.007) and LBSQ fat (0.37 ± 0.25 vs. 0.22 ± 0.20 μmol ⋅ kg fat⁻¹ ⋅ min⁻¹; P = 0.005); storage rates were significantly greater in UBSQ than LBSQ fat in both sexes. During walking, UBSQ palmitate storage did not differ between sexes, whereas LBSQ storage was greater in women than men (0.40 ± 0.22 vs. 0.25 ± 0.15 μmol ⋅ kg fat⁻¹ ⋅ min⁻¹; P = 0.01). In women only, walking palmitate storage was significantly greater in LBSQ than UBSQ fat. Adipocyte CD36 and diacylglycerol acyltransferase (DGAT) correlated with LBSQ palmitate storage in the postprandial and walking condition, respectively. We conclude that UBSQ fat is the preferred postprandial FFA storage depot for both sexes, whereas walking favors storage in LBSQ fat in women. Transmembrane transport (CD36) and esterification into triglycerides (DGAT) may be rate-limiting steps for LBSQ FFA storage during feeding and exercise.