Beneficial Effects of Fermentation of Whole Grains (WG) and Whole Grain Resistant Starch (RS) in Lean Zucker Diabetic Fatty (ZDF) Rats
Authors: Guice Justin , Page Ryan , Carvajal‐Aldaz Diana , Raggio Anne , Obanda Diana , Durham Holiday , Marco Maria , Tuuri Georgianna , Martin Roy , Marx Brian , Coulon Diana , Keenan Michael 
Published: November 2023

Whole grain components have been shown to have a beneficial role concurrent with and independent of purified resistant starch (RS2) through intestinal fermentation when delivered as a fermentable dietary fiber. As Americans consume less than half of the recommended amounts of fiber, determining if a lower fiber dose can still provide benefits through use of WG and RS may still allow for health benefits in the context of lower intake. The current study was designed to delineate optimal health effects from a whole grain prebiotic using a dose response, where the beneficial effects of fermentation were expected to be observed beginning at 5% (wt diet). Estimates for comparing fiber in humans vs. rats are ~10% for equivalence. Previous studies with obese ZDF rats showed robust effects of fermentation on gut microbiota with no reduction of abdominal fat when fed RS. Additionally, Sprague Dawley (SD) rats demonstrated a significantly increased fermentation, though not as robust as ZDF rats, when fed WG, RS, and WG+RS diets, but also statistically significant differences in abdominal body fat as compared to obese ZDF rats. Isocaloric moderate fat (3.7 kcal/g, ~30% of energy) diets were developed with the following starch sources: control starch with no WG or RS [CON], natural WG waxy corn flour with low RS (35.1 %WG) [WGC], or increasing levels of a whole grain high amylose maize resistant starch (WGRS) [HMWG: 5 (9.3), 10 (18.6), 15 (27.9), 20% (37.2%) RS (%WG)]. The six diets were fed to lean ZDF rats for eight weeks (n=11; n=12 for 5%, 10% HMWG). Single degree of freedom contrasts (WGC vs. CON, 5%, 10%, 15%, 20%) were performed at p<0.05. Beginning at 5% HWMG, pH had significant reduction as compared to WGC. Cecum weight significantly increased from 10% HMWG on. All short chain fatty acid (SCFA) measurements were significantly different for WG vs. CON. SCFA acetate and propionate showed a significant increase at 5% and increased consecutively through 20%, while butyrate increased at 15% and 20%. No significant differences were observed for food and energy intake and percentage abdominal fat/emboweled body wt (gut contents removed). At 5% HMWG, fermentation effects differed overall from the WG control. An indirect comparison of lean ZDF rats and obese ZDF rats has shown similarity in fermentation and no changes in body fat. As WGRS dosage increased, gut health benefits (fermentation parameters) increased, but did not affect food and energy consumed or abdominal fat. WG flour alone promoted fermentation with RS1, a component of the WG kernel, and WGRS (RS1+RS2) promoted greater fermentation. Replacing traditional starch for a whole grain starch is beneficial, while replacing it with a whole grain with resistant starch, as low as 5%, is better. These results suggest that a lower level of intake of fermentable fiber as RS is beneficial, but show that substantial WG (35.1%) with only low RS1 (2%) also had beneficial effects.

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USDA–NIFA #2014–67017–21760, LSU AgCenter and Ingredion Incorporated.