Postprandial lipemia after short-term variation in dietary fat and carbohydrate

Replacement of dietary fat with carbohydrate may not reduce the overall ris k of coronary heart disease (CHD), because this elevates plasma triacylglyc erol (TAG) concentrations. The lipoproteinemic effects of a high-carbohydra te diet are likely to be more marked shortly after the initiation of such a diet than after longer periods of intervention during which adaptive proce sses may counteract the initial effects. Therefore, we studied the postpran dial responses to a standard meal after 3-day dietary intervention periods. An additional objective was to establish a model for future study of the m echanisms involved. Nine normolipidemic men consumed the meal (1.2 g fat, 1 .1 g carbohydrate, and 0.2 g protein per 1 kg body mass) after 3 days on a high-carbohydrate diet (68% +/- 3% energy from carbohydrate, mean +/- SD) a nd also after 3 days on an isoenergetic high-fat diet (66% +/- 5% energy). Venous blood samples were obtained from fasted subjects and for 6 hours aft er the meal. In the fasted state, TAG was higher after the high-carbohydrat e diet (1.18 +/- 0.18 v 0.62 +/- 0.09 mmol/L, mean +/- SEM, P = .02) and hi gh-density lipoprotein (HDL) cholesterol was lower (1.01 +/- 0.08 v 1.10 +/ - 0.09 mmol/L, P = .002). The area under the plasma TAG concentration versu s time curve was 42% +/- 7% higher after the high-carbohydrate diet (P = .0 03). After the high-carbohydrate diet, the postprandial insulin response di d not differ between trials, but glucose and 3-hydroxybutyrate responses we re lower (P = .009 and P = .02, respectively) and the lactate response was higher(P = .001). Plasma nonesterified fatty acids (NEFAs) were lower after the high-carbohydrate diet in the fasted state and for 4 hours postprandia lly, but were higher thereafter (interaction of time x trial, P = .001). Th ese results indicate that compared with a high-fat diet, the plasma TAG res ponse to a standard high-fat meal is markedly higher after a few days on a high-carbohydrate diet, with major differences in the associated metabolic milieu. The magnitude of these changes and the rapidity with which they dev eloped suggest that this model may be attractive for future studies of the underlying mechanisms. Copyright (C) 2000 by W.B. Saunders Company.