Accumulation of postprandial triacylglycerol-rich lipoproteins is generated by assimilation of ingested dietary fat and has been increasingly related to atherogenic risk. Nevertheless, the influence of different kinds of dietary fatty acids on postprandial lipid metabolism is not well established, except for (n-3) polyunsaturated long-chain fatty acids. Our goal was to evaluate the effects of test meals containing a common edible fat source of saturated (butter), monounsaturated (olive oil) or (n-6) polyunsaturated (sunflower oil) fatty acids on postprandial lipid and triacylglycerol-rich lipoprotein responses. After a 12-h fast, 10 healthy young men ingested mixed meals containing 0 g (control) or 40 g fat, provided as butter, olive oil or sunflower oil in a random order. Fasting and postmeal blood samples were collected for 7 h. The no-fat test meal did not elicit any change over baseline except for plasma phospholipids, insulin and nonesterified fatty acids. Conversely, the three fat-containing meals elicited bell-shaped postprandial changes (P < 0.05) in serum triacylglycerols, free and esterified cholesterol, and nonesterified fatty acids. The butter meal induced a lower postprandial rise of triacylglycerols in serum and chylomicrons (incremental AUC, mmol.h/L: 0.72) than the two unsaturated oils (olive oil: 1.6, sunflower oil: 1.8), which did not differ. Circulating chylomicrons were smaller after the butter meal than after the two vegetable oil meals. The in vitro susceptibility of circulating chylomicrons to hydrolysis by postheparin plasma was higher after sunflower oil than after butter or olive oil. We conclude that butter results in lower postprandial lipemia and chylomicron accumulation in the circulation of young men than olive or sunflower oils after consumption of a single mixed meal.

The effect of the ingestion of beta-carotene with medium-chain triglycerides (MCT) or long-chain triglycerides (LCT) on the bioavailability and the provitamin A activity of beta-carotene was investigated in humans. Sixteen healthy young men ingested, on two different days, a test meal containing 120 mg beta-carotene incorporated into 40 g LCT (LCT meal) or 40 g MCT (MCT meal). This meal was followed 6 h later by a beta-carotene-free meal containing 40 g LCT. Chylomicron beta-carotene, retinyl palmitate and triglycerides were measured every hour for 12.5 h after the first meal. No significant increase in chylomicron triglycerides was detected for the 6 h after the MCT meal intake, whereas a significant increase in chylomicron triglycerides was observed after the LCT meal intake. The chylomicron beta-carotene and retinyl palmitate responses to the MCT meal (0-6 h area under the curves, AUC) were significantly (P< 0.05) lower [AUC = 68.1 +/- 26.8 and 43. 4 +/- 10.4 nmol/(L.h), for beta-carotene and retinyl palmitate, respectively] than those obtained after the LCT meal [301.4 +/- 64.0 and 166.0 +/- 29.0 nmol/(L.h), respectively]. The chylomicron beta-carotene and retinyl palmitate responses obtained after the beta-carotene-free meal (6-12.5 h AUC) were also significantly lower when the first meal provided MCT rather than LCT. The chylomicron (retinyl palmitate/beta-carotene) ratios were constant during the postprandial periods, whatever the meal ingested. We conclude that the chylomicron beta-carotene response is markedly diminished when beta-carotene is absorbed with MCT instead of LCT. This phenomenon is apparently due to the lack of secretion of chylomicrons in response to MCT; however, a lower intestinal absorption of beta-carotene or a higher transport of beta-carotene via the portal way in the presence of MCT cannot be ruled out. Finally, the data obtained show that MCT do not affect the rate of intestinal conversion of beta-carotene into vitamin A.

The effect of ageing on vitamin E bioavailability in humans was assessed by comparing chylomicron and plasma alpha-tocopherol postprandial concentrations after a dose of vitamin E (432 or 937 IU as d1-alpha-tocopherol acetate), in eight young (20-30 years old) and eight healthy elderly men (64-72 years old). The fasting plasma alpha-tocopherol concentration was significantly higher in the elderly (33 +/- 2 mumol L-1) than in the young (22 +/- 2 mumol L-1). In both groups, the plasma and chylomicron alpha-tocopherol postprandial concentrations were significantly, approximately twofold, higher after the 937-IU meal than after the 432-IU meal. For both test meals, the chylomicron alpha-tocopherol areas under the curve were significantly lower in the elderly than in the young subjects: 98.9 +/- 16.5 (young group) vs. 55.3 +/- 7.8 (elderly group) mumol L-1 h for the 937-IU test meal and 60.4 +/- 14.1 (young group) vs. 26.0 +/- 7.6 (elderly group) mumol L-1 h for the 432-IU test meal, whereas the plasma alpha-tocopherol area under the curve was significantly higher in elderly than in young subjects: 337.56 +/- 16.11 (937-IU test meal) vs. 159.81 +/- 35.55 (432-IU test meal) mumol L-1 h in the young group and 709.55 +/- 69.33 (937-IU test meal) vs. 436.39 +/- 41.08 (432-IU test meal) mumol L-1 h in the elderly group. We concluded that (a) the amount of vitamin E appearing in plasma is proportional to the dose ingested (up to 937 IU); (b) the intestinal absorption of vitamin E is not increased, even possibly decreased, in the elderly; and (c) the amount of vitamin E transported by non-chylomicron lipoproteins is apparently higher in the elderly. This suggests that vitamin E postprandial transport is affected by ageing, mainly as the consequence of age-related modifications of lipoprotein metabolism.

To investigate the mechanisms behind the serum cholesterol-lowering effect of oat fiber, we simultaneously measured postprandial lipid responses, serum lathosterol concentrations, and small bowel excretion of fat and sterols in ileostomy subjects given test meals high or low in oat fiber. Six ileostomy subjects (three women and three men) were served an oat-bran test meal (OB; 16.3 g fiber) and a wheat test meal (6.3 g fiber) in random order. After the postprandial 7-h period, a controlled, low-fat, cholesterol-free diet was served and ileostomy effluent was sampled throughout the 24-h period. Bile acid and fat excretion (24 h) increased by 93% and 146%, respectively (P < 0.05), and total and endogenous cholesterol excretion decreased by 14% and 19%, respectively (P < 0.05), after the OB test meal. The change in hepatic cholesterol synthesis was strongly related to the change in bile acid excretion (Spearman r = 0.89, P < 0.02). The postprandial chylomicron lipid concentration tended to be lower after the OB test meal (-43% for cholesterol, P = 0.07) whereas there was no difference in cholesterol absorption measured by isotope in five subjects. The main effect of the viscous oat beta-glucan seems to be related to increased bile acid excretion and subsequent changes in synthesis and endogenous excretion of cholesterol. An additional effect may have been a delay in the micellar lipid solubilization process and a consequent reduction in the secretion of chylomicrons into the circulation.