Postprandial lipid and carbohydrate responses after the ingestion of a casein-enriched mixed meal.

BACKGROUND Postprandial lipemia is markedly modulated when carbohydrates are added to a fatty meal. The effect of added protein is less known, however, and the data are controversial. OBJECTIVE We investigated the effects of casein added to various fat-rich meals in the absence and presence of oligosaccharides. DESIGN Four different test meals were given to 24 healthy volunteers: 1) fat alone, consisting of 3 g cream/kg body wt; 2) fat plus 75 g oligosaccharides; 3) fat plus 50 g sodium caseinate; and 4) a combination of all 3 components. Blood samples were taken before the meals and 1, 2, 3, 4, 5, 6, 7, and 8 h thereafter. The variables measured were serum free fatty acids, arginine, glucose, insulin, and C-peptide as well as triacylglycerol in serum, in chylomicrons, and in VLDL. Gastric emptying was monitored with the use of a (13)C breath test. RESULTS Addition of oligosaccharides resulted in the known delay and reduction in postprandial lipemia. Casein caused additional effects: chylomicrons were further reduced and delayed, independently of gastric emptying. C-peptide and insulin, as expressed by their areas under the curves, were raised not only during the early response to the glucose load but also in the postabsorptive state. Concentrations of free fatty acids, which were markedly suppressed by 24% after oligosaccharides alone, were lowered a further 20% after the addition of casein. CONCLUSIONS Casein added to a fatty meal lowers free fatty acids markedly in the postprandial and postabsorption phases, probably via its insulinotropic activity. Postprandial lipemia is also moderately reduced.