Year: 2016
Type: dissertation
Abstract: Short-chain fatty acids (SCFA) are produced by colonic microbiota, mostly from dietary fiber. Mice studies have shown that excess production of SCFA by the ‘obese microbiota’ (increased Firmicutes and decreased Bacteroidetes), may promote obesity via increased colonic energy availability. However, other studies have shown that colonic fermentation of dietary-fiber to SCFA may play a role in preventing obesity and diabetes. Thus, the primary goals of this work were to investigate whether overweight and obese (OWO) humans produce SCFA more efficiently than lean (LN) humans, and whether SCFA from colonic fermentation of two different fibers affect appetite hormone and glycemic responses. To achieve these goals, 2 studies in LN and OWO human subjects were performed. The first study confirmed higher fecal SCFA concentrations in OWO than LN humans. This could have been due to more efficient SCFA production by the ‘obese microbiota’, since colonic SCFA absorption, dietary intakes and markers for gut transit time were similar in LN and OWO subjects and, therefore, could not explain the difference in fecal SCFA between the groups. However, the second study did not confirm the higher SCFA concentrations in feces or in blood (either at fasting or postprandially following fiber consumption) in OWO compared to LN humans. Unexpectedly the increase in SCFA from inulin or resistant-starch’s fermentation did not affect glycemia or appetite hormone responses (excluding a possible effect of inulin on ghrelin). On the other hand, both fibers induced early effects that were not likely related to colonic fermentation: resistant-starch significantly reduced free-fatty acid rebound and second-meal glucose and insulin responses, while inulin significantly elevated the satiety hormone PYY. The results do not support the hypothesis that overweight/obesity is associated with increased colonic SCFA production. The acute effects of consuming resistant starch to reduce glycemic responses and of inulin to improve appetite hormones profiles are not likely a result of their fermentation to SCFA. However, a longer adaptation to high fermentable fiber intakes may yield different results. Therefore, longer term and larger scales human studies are warranted.
Source: TSpace (University of Toronto)
Author: S Rahat-Rozenbloom
Language: English
Topic: Gut microbiota and health
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2727374368