In Vitro Degradation and Fermentation of Three Dietary Fiber Sources by Human Colonic Bacteria

Abstract

Although clinical benefits of dietary fiber supplementation seem to depend partially on the extent of fiber degradation and fermentation by colonic bacteria, little is known about the effect of supplemental fiber type on bacterial metabolism. In an experiment using a non-adapted human bacterial population from three normal subjects, extent of in vitro fermentation was greater for gum arabic (GA) than for psyllium (PSY), which was greater than that for carboxymethylcellulose (CMC). In a separate experiment, in vitro incubation with feces from 52 subjects with fecal incontinence, before and after random assignment to and consumption of one of three fiber (GA, PSY, or CMC) supplements or a placebo for 20-21d, indicated that prior consumption of a specific fiber source did not increase its degradation by fecal bacteria. Results suggest that the colonic microbial community enriched on a particular fiber substrate can rapidly adapt to the presentation of a new fiber substrate. Clinical implications of the findings are that intake of a fiber source by humans is not expected to result in bacterial adaptation that would require continually larger and eventually intolerable amounts of fiber to achieve therapeutic benefits.

The effects of type of protein and fibre fermented <i>in vitro</i> with different pig inocula on short-chain fatty acids and amines concentrations

“…The diversity of these results may be partly explained by different experimental methods, including the origin of sampled material or inoculum. The use of faecal inoculum in in vitro studies of fermentation is a common practice (Coles et al, 2005) and faeces are treated as the obvious source of colonic bacteria (Jha et al, 2011;Bliss et al, 2013). Our results showing that fermentation with colonic digesta yields greater total SCFA concentrations and is more discriminative than fermentation with fresh faecal inoculum, agree with the results of Monsma and Marlett (1995) who found greater initial and maximum production of SCFA after fermentation with caecal than faecal inoculum in rat model.…”

The Role of Legumes in Human Nutrition

“…In addition, dietary fibre, particularly soluble dietary fibre, has the ability to lower blood cholesterol, improve glucose tolerance and reduce glycaemic response by forming a protective gel lining along the intestinal walls thus reducing glucose and cholesterol assimilation into the bloodstream [22,24,25]. Insoluble dietary fibres are porous, have low densities, increase faecal bulk and promote normal laxation [26][27][28]. As such, legumes are an invaluable component of the human diet.…”

Impact of Dietary Fibers on Nutrient Management and Detoxification Organs: Gut, Liver, and Kidneys

“…The susceptibility of fermentation by the gut microbiota has also been used to classify DF as fermentable or nonfermentable. The degree of fermentation is often assessed by the microbial production of SCFAs or the disappearance of fiber from the feces (18). Each classification system includes fibers that vary greatly in composition and structure (19), and these differences in monosaccharide content, glycosidic linkages, degree of polymerization (length of molecule), degree of substitution (side chains), and fiber preparation can contribute to the different physiologic outcomes associated with certain fiber types (20).…”