Nutritional effects of resistant starch and sugar-beet fibre. Short term studies in ileostomy subjects

Abstract

Background: Starch is the most important source of energy in human diets. Part of the starch in the diet, resistant starch (RS), escapes digestion and absorption in the small bowel, contrary to the earlier view that all starch was completely digested and absorbed. RS provides a new means to alter the nutritional properties of food products, however little is known about the nutritional effects of RS in the small bowel. Sugar-beet fibre (SBF), a dietary fibre enrichment source containing pectin and hemicellulose, has potential serum-cholesterol lowering properties.Aims: The aims were to a) compare in vivo measurement of RS in the ileostomy model with previously published intubation data; b) study the nutritional effects of the addition of RS to the diet on small bowel excretion of energy, nutrients and sterols; c) study the effect of SBF on small bowel excretion of sterols, and d) study fermentation patterns of RS by using ileal effluents for in vitro fermentation. Methods: The short term effects of the addition of different types of RS or SBF to the diet, on small bowel excretion of energy, nutrients and sterols were studied in groups of 7ñ10 ileostomy subjects.Results: In vivo measurement of RS in the ileostomy model and intubation technique gave comparable results. Addition of RS to the diet increased ileal excretion of energy. The ileal excretion of fat, nitrogen and minerals was not influenced, except for a small, but nutritionally not important increase in iron excretion on addition of raw banana flour (RBF). Addition of bean flakes compared to potato flakes to the diet resulted in a lower blood glucose response and a slight increase in the ileal excretion of nitrogen and magnesium. Total energy excretion after ingestion of the bean flake and potato flake diets was 1583 (SE 91) and 987 (SE 77) kJ/d, respectively. Ninety-eight per cent of the energy providing nutrients in the effluents could be characterised. The mean amount of RS recovered after ingestion of an ordinary low-fibre Swedish diet was 5 (range 3.2ñ6.4) g/d.Ileal excretion of bile acids was reduced after addition of retrograded high amylose corn starch to the diet compared to ordinary corn starch, however RBF compared to digestible banana flour did not significantly change sterol excretion. Addition of SBF increased net cholesterol excretion and reduced total bile acid excretion by while total sterol excretion remained unchanged. In vitro fermentation of ileum effluents obtained after ingestion of a high-RS diet compared to a low-RS diet increased butyrate concentration. RS from banana was slowly fermented.Conclusions: The ileostomy model was found to be a reliable model for in vivo measurement of RS. Addition of RS to the diet increased ileal excretion of energy without significantly altering excretion of other nutrients. The nutritionally important effect of RS is the reduced blood glucose response and the potentially beneficial effect in the colon, such as increased butyrate production. Sugar-beet fibre did not increase total sterol excretion from the small bowel, making a considerable serum-cholesterol lowering effect unlikely