Dissertation

Postprandial lipid metabolism with ingestion of defined butterfat fractions in the rat

Lai, Hui-Chuan

1994

Overview

The effect of different dietary saturated fats on postprandial lipid metabolism is unclear. We compared fasting and postprandial lipid responses in rats fed polyunsaturated corn oil or one of four saturated fats: palm oil, intact butterfat, a liquid butterfat fraction enriched in 18:1 and a solid butterfat fraction enriched in 16:0 and 18:0. Rats were adapted to eat a daily 3-hr meal containing 16% fat (w/w) and 0.017-0.048% cholesterol for 3-4 weeks. Postprandial lipemic responses were determined by measuring (1) plasma cholesterol, triacylglycerol (TAG), free glycerol and insulin levels, (2) postheparin plasma lipoprotein lipase (PHLPL) activity, (3) TAG content remaining in the gastrointestinal tract, and (4) lymph chylomicron secretion rates. Ingestion of corn oil, compared to all four saturated fats, resulted in (1) significantly lower fasting and postprandial plasma TAG and cholesterol levels and 50-100% less TAG accumulation (mM/24 hr), (2) higher PHLPL activities (0-9 hr), free glycerol (2.5-4.5 hr) and insulin (2.5 hr) levels, and (3) no differences in lymph chylomicron TAG or cholesterol output (mg/24 hr). This suggests that increased clearance was responsible for the reduced postprandial lipemia noted with corn oil. Ingestion of palm oil, liquid and solid butterfat resulted in similar postprandial plasma TAG levels and chylomicron TAG secretion rates. However, significantly higher PHLPL activities (0-9 hr) were noted with ingestion of palm oil compared to liquid or solid butterfat and larger chylomicron size was noted with infusion of liquid compared to solid butterfat. This suggests that postprandial lipid metabolism differed with palm oil, liquid and solid butterfats despite similar absorption. Analyses of fatty acid and TAG profiles (total acyl carbon number or Cn) demonstrated that short chain fatty acids (4:0 and 6:0) and small TAG molecules (C $\\sb{30}$ -C $\\sb{34}$ ) of the liquid and solid butterfats were preferentially hydrolyzed by gastric lipolysis and did not appear in lymph chylomicrons. In conclusion, ingestion of corn oil resulted in reduced postprandial lipemia compared to saturated fats, however, each saturated fat demonstrated an unique effect on postprandial lipid metabolism. Differences in fatty acid and TAG profiles may contribute to the differential postprandial lipemic responses noted in these studies.

• Publisher: ProQuest Dissertations & Theses
• Subject: Animal sciences / Livestock / Nutrition
• ISBN: 9798208661246