INTESTINAL TRANSPORT AND FERMENTATION OF RESISTANT STARCH EVALUATED BY THE HYDROGEN BREATH TEST

Objective: To study fermentability of different samples of resistant s tarch (RS), compared to one another and to lactulose, and to study the effect on gastric emptying of addition of RS to test meal. Finally to study if adaptation to RS results in a measurable change in fermentat ion pattern, (H-2/CH4 production). Sources of RS: Raw potato starch (R PS), 58% RS; corn flakes (CF), 5% RS; hylon VII high amylomaize starch , extrusion cooked and cooled (HAS) 30% RS; highly retrograded hylon V II high amylomaize starch (HRA) 89% RS. Design: (1) Fermentation: seve n healthy volunteers ingested in randomized order 50 g RPS, 100 g CF, 75 g HAS, 25 g HRA. End-expiratory (H)2/CH4 was measured every 30 min for 12 to 22 hours post-ingestion as a measure of fermentation. A dose -response study of RPS, 5, 10, 25, 50, 75 and 100 g was performed. (2) Adaptation: In five 3-week periods seven volunteers added daily to th eir usual diet 50 g of either RPS, HAS, oat bran, wheat bran or common maize starch. The polysaccharides were administered in randomized ord er. The test periods were separated by 1 week's wash out. Basic end-ex piratory H-2/CH4 was measured once a week prior to and during the test periods. (3) Gastric emptying: The rate of increase in blood glucose was measured after test meals consisting of 50 and 100 g of RPS, 50 g HAS and 50 g glucose dissolved in a gel, alone, and mixed with 25 g of RPS. As controls we chose wheat bran and oat bran. Results: (1) We fo und that RPS is fermentable, although the cumulated excessive H-2 prod uction after 50 g RPS corresponding to 29 g RS was clearly less than a fter 10 g lactulose. The time from ingestion of RPS to a sustained inc rease in end-expiratory H-2 (apparent transit time; 5-11 h) was longer than lactulose (1-4 h), indicating either a slow passage through the small intestine or a slow fermentation rate. 100 g of corn flakes (4.6 g RS) resulted in a measurable increase in H-2 production, equivalent to 10-20 g RPS, whereas neither of the two samples of hylon VII high amylomaize resulted in any significant increase in H-2 production. The dose-response study with RPS showed that even 5 g of RPS resulted in a measurable increase in end-expiratory H-2, and increasing doses from 5 g to 100 g resulted in a seemingly exponential increase in H-2 prod uction. (2) 3 weeks' daily administration of HAS resulted in a slightl y elevated increase in basic end-expiratory H-2, although the increase did not reach statistical significance. RPS resulted in a sustained i ncrease in basic end-expiratory H-2. Both RS samples increased measura ble end-expiratory CH4 in volunteers with measurable CH4 production af ter a lactulose load, but 3 weeks' daily challenge with these slowly f ermentable substrates did not increase measurable CH4 in volunteers, w ho prior to the study only produced CH4 intermittently. (3) The rate o f increase in blood sugar was unaffected by addition of RS or non-star ch-polysaccharides to the test meal, indicating that addition of the p olysaccharides does not affect gastric emptying.