Recent human studies have shown that cold exposure increases lipid oxidation, even when the oxidation of circulating free fatty acid (FFA) is markedly reduced by the ingestion of nicotinic acid, thus seriously questioning the importance of FFA for lipid oxidation in the cold-exposed humans. It was therefore hypothesized that similarly to prolonged exercise, fatty acids from plasma triglycerides (TG) are important energy substrates for oxidation during prolonged cold exposure in man. The goal of this study was to determine the influence of cold exposure on an index of plasma TG utilization, the intravenous fat tolerance test (IVFTT). To evaluate the possibility of a delayed increase in fat tolerance, a second cold exposure and an IVFTT were also performed 24 hours after the first cold exposure. Seven healthy males (fasting, seminude) were subjected to an IVFTT (1 mL/kg 10% Intralipid) on three occasions while resting for 160 minutes: (1) at 29 degrees C, (2) in the cold (10 degrees C, 1 m/s wind), and (3) at 10 degrees C 24 hours after the first cold test. One week separated the warm test from the cold tests. Cold exposure reduced mean body temperature by 3.4 +/- 0.1 degree C and increased energy expenditure 2.5 times in comparison to warm values (P less than .01). It also increased fat oxidation by 70% (P less than .05) and plasma glycerol levels (P less than .05), but did not alter fat tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)