Carbohydrates' impact on hepatic and intestinal lipoprotein accumulation

Nutrition Research Newsletter, Nov, 2004

The healthy diet currently recommended by most Westernized countries is a low-fat, low-cholesterol, high carbohydrate diet. There is increasing interest in the effects of the amount and type of dietary carbohydrate on the metabolic profile and health-related issues, including the metabolic syndrome and cardiovascular disease risk. Some clinical studies show that highly digestible carbohydrate diets may lead to an increase in fasting plasma triacylglycerol concentrations as a result of the accumulation of hepatic VLDL and chylomicron remnants. Regarding the glycemic index (GI), there his some evidence to show that in comparison with high-GI diets, low-GI diets improve metabolic profiles of healthy subjects, and patients with type 2 diabetes, overweight subjects, and glucose-intolerant patients.

As the prevalence of type 2 diabetes and obesity rises, the question of the best suitable diet remains. Therefore, a study was signed to test the hypothesis that sources of dietary carbohydrates with different slowly digestible carbohydrate contents could induce different glycemic and insulinemic responses that alter postprandial lipoprotein metabolism differently in insulin-resistant subjects. Nine nondiabetic, android-type obese subjects (8 women with a waist circumference > 88 cm and 1 man with a waist circumference > 102 cm) with a mean age of 35 years (range: 25-45 years) were recruited for this study. The subjects' mean body mass index (BMI) was 36.4 [ or -] 1.8. All the subjects had insulin resistance according to their homeostasis model assessment scores. The usual diet was monitored through the use of a 3-day food record.

Two test meals, differing only in the source of carbohydrate, were designed. The carbohydrate sources compared were cereal foods: experimental plain wheat biscuits (biscuit meal) and usual ready-to-eat wheat flakes (flakes meal). The cereal products were processed differently, which led to different contents of slowly available glucose (SAG). The SAG content has been negatively correlated with GI. The subjects ingested the 2 test meals in a random order, separated by a 1-week interval. A baseline (0 hour) fasting blood sample was collected. Blood samples were collected every half hour during the first 2 hours and every hour until 6 hour after the meal.

The postmeal 0-2 hour areas under the curve (AUCs) for glycemia and insulinemia were significantly lower (P < 0.05) after the biscuit meal than after the flakes meal. Plasma triacylglycerol concentrations increased significantly after the flakes meal but not after the biscuit meal (1.5-fold higher 0-6 hour AUC for the flakes meal). Apolipoprotein B-100 concentrations in the triacylglycerol-rich lipoprotein fraction increased significantly 2 hours after the flakes meal but not after the biscuit meal (3-fold higher 0-6 hours AUC for the flakes meal). Apolipoprotein B-48 concentrations increased (P < 0.05) 4 hours after the flakes meal but not after the biscuit meal (2.3-fold higher 0-6 hours AUC for the flakes meal).

Mixed meals, containing slowly digestible carbohydrate, induces low glycemic and insulinemic responses reduced the postprandial accumulation of both hepatically and intestinally derived triacylglycerol-rich lipoproteins in obese subjects with insulin resistance.

A. Harbis, S. Perdreau, S. Vincent-Baudry, et al. Glycemic and insulinemic meal responses modulate postprandial hepatic and intestinal lipoprotein accumulation in obese, insulin-resistant subjects. Am J Clin Nutr; 896-902 (October, 2004). [Correspondence: D Lairon, UMR U476-INSERM/INRA, Faculte de Medecine, 27 Boulevard Jean Moulin, 13885 Marseille Cedex 05, France. E-mail: denis.lairon@medecine.univmrs.fr].