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The effect of changing wheat particle size on human post-prandial metabolism and degree of starch digestion.
T. GRASSBY (1), C. Edwards (1), M. Grundy (1), S. Berry (1), J. Sanderson (1), P. Ellis (1). (1) King's College London, London, United Kingdom

Recent evidence suggests that dietary fiber, in the form of plant cell walls, can influence the extent, rate and location of nutrient release in the human gut. Understanding of the changes that intact cell walls undergo during digestion is limited, as is their effect on nutrient digestion and absorption. The aims of this study were to investigate the effects of cell wall encapsulation of starch on: 1 - postprandial glycemia and insulinemia, 2 – starch digestion. Healthy volunteers (n=9) with an ileostomy (allowing retrieval of partially digested test meals before bacterial degradation in the colon) were assigned to receive two wheat-based test meals in a randomized cross-over study (researcher blind). The meals consisted of durum wheat porridge made from flour or 2 mm chunks (55 g starch). The flour had essentially no intact cells present, whereas the chunks had a high proportion of intact cells. Venous blood was collected at regular intervals for 4 hours after the test meals, and analyzed for glucose, insulin, c-peptide and other gut hormones. Ileal effluent was collected for 24 hours after the test meals, and tested for starch content. The flour meal induced a significantly larger glycaemic and insulinemic response than the 2 mm chunk meal (P<0.05, ANOVA). Microscopy of effluent showed a progressive loss of starch from the periphery of the 2 mm chunks. Approximately 6% of the starch in both test meals remained undigested when recovered from the terminal ileum. Cell wall encapsulation attenuates postprandial glycemia and insulinemia, but does not increase resistant starch content. This study demonstrates how changes to the processing of wheat can affect postprandial metabolism. This trial was approved by NHS Kent Research Ethics Committee (12/LO/1016) and registered at ukcrn.org.uk (13108). It was funded by the Biotechnology and Biological Sciences Research Council.

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