Use of structured triacylglycerols containing predominantly stearic and oleic acids to probe early events in metabolic processing of dietary fat.

Early events in the metabolic processing of dietary triacylglycerol may have an important impact on subsequent development of risk factors for coronary heart disease. We have used structured triacylglycerols containing predominantly stearic or oleic acids at the sn -2 position to probe aspects of the processing of dietary fatty acids presented to adipose tissue in chylomicron-triacylglycerol. Studies were conducted on 14 healthy women who were given meals containing 85 g carbohydrate and 60 g of either of the two structured triacylglycerols in random order. Systemic concentrations and arterio-venous differences across adipose tissue for plasma triacylglycerol and non-esterified fatty acids were measured, together with analysis of the fatty acid composition of the relevant fractions. The stereo-specific structure of the ingested triacylglycerol was largely preserved in chylomicron-triacylglycerol. Systemic concentrations of total and individual non-esterified fatty acids were not significantly different after ingestion of the two fats, nor were their rates of release across adipose tissue. The composition of non-esterified fatty acids released from adipose tissue changed after the meal to reflect more closely the composition of the triacylglycerol ingested, but again no significant differences were observed between the two test meals. There was no detectable release of monoacylglycerol from adipose tissue after either test meal. We conclude that the environment for lipoprotein lipase action in adipose tissue in vivo is likely to be highly organized, such that there is no release of monoacylglycerol, nor preferential uptake or release of fatty acids from chylomicron-triacylglycerol according to the nature or the position within triacylglycerol of the fatty acid.