Background – Experimental and epidemiological data suggest that dietary fibre and resistant starch (RS) promote bowel function through faecal bulking and short-chain fatty acid (SCFA) production. Our data has recently shown that dietary n-3 polyunsaturated fatty acids (PUFA) from fish oil (FO) also have important actions on the gut (1). Objective – To feed normotensive and the spontaneously hypertensive rat (SHR) diets supplemented with FO and RS and examine indices of gut health including effects on in vitro contractility.
Design – In experiment 1, young Sprague Dawley (SD) rats wed fed 4 diets that contained 100 g/kg fat as sunflower oil or FO and with 10% fibre supplied as α-cellulose or high amylase maize starch rich in RS. In experiment 2, older SHR and WKY control rats were fed 3 diets with 50 g/kg fat as lard, canola oil, or FO. We measured gut tissue fatty acid composition, muscarinic receptor binding properties, the SCFA pool and agonist-induced gut contraction. Outcomes – FO supplementation lead to increased n-3 PUFA content of gut tissue while RS resulted in increased caecal content of SCFA, especially as butyrate, and lowered pH. There where no changes in total muscarinic binding in gut tissue of older SHR. However, in young SD rats FO supplementation altered the sensitivity of the M1 receptor subtype compared to the other diets. In SD ileum, FO feeding also led to higher 8-iso-PGE2 (83%) PGE2 (259%) and PGF2α-induced (203%) maximal contractility with a RS effect noted for carbachol (105%). Lower prostanoid effects in young SD rats and older SHR were also enhanced by FO. It was noted for SHR, FO supplementation also resulted in the first observation of increased maximal contraction of the colon. While a 5% canola oil diet rich in α-linolenic acid lead to a marginal increase in total tissue n-3 PUFA in SHR ileum, there were no effects on contractility.
Conclusion – Although little interactive effects were noted for FO and RS, the data suggests developmental changes in ileal receptor systems with independent effects of RS and FO on some bowel properties of juvenile rats. In older SHRs, FO supplementation increased contractility of ileum and colon and restored depressed prostanoid contractility in ileum with docosahexaenoic acid (DHA) indicated as the active agent. FO and RS produce positive outcomes for bowel health, likely by independent mechanisms which may be of interest to the food industry. Reference
1 Patten GS, Conlon MA, Bird AR, Adams MJ et al. Interactive effects of resistant starch and fish oil on SCFA production and agonist-induced contractility in ileum. Dig Dis Sci 2006;51:254-61.