To determine whether an increased risk for atherosclerosis in older humans is related to changes in postprandial lipoprotein metabolism, we compared the dynamic profiles (0-10 hours) of triglyceride (Tg)-rich lipoproteins and the Tg content in VLDL subfractions in elderly and young subjects after an oral fat load. The plasma Tg response curves displayed significant differences between the groups at all times. Postprandial triglyceridemia was quantified from the plasma response curves as an incremental area, and was significantly different in the two groups (young subjects 231.9 +/- 199.6 vs elderly subjects 511.0 +/- 305.6 mg/dL x 10 hr, p = 0.036). The more scattered VLDL-Tg values were significantly different compared to values at baseline and 6 hours after fat load. Tg baselines in the four VLDL subfractions (expressed as percentages) were higher in the larger particles (B Sf = 175-400) in the elderly subjects, and in the smaller, denser particles (D Sf = 20-100) in the young subjects. In both groups, postprandial hyperlipidemia increased the Tg content of the larger, less dense particles (Sf more than 400), and reduced that of the denser particles. These variations usually coincided with the plasma Tg and VLDL peaks: 63% to 70% above the Tg baseline between the 2nd and 4th hour in all the young subjects: 48% to 68% above the baseline between the 4th and the 6th hour in all the elderly subjects. Total cholesterol variations showed no significant differences between the two groups at any time. All subjects tested for the missense mutation at codon 188 of the human lipoprotein lipase (LPL) gene resulted noncarriers of LPL mutant alleles. Our data show that, after a fatty meal, healthy elderly subjects tend to present prolonged postprandial hypertriglyceridemia, suggesting an atherogenic behavior of their lipid metabolism.