Guar, but not psyllium, increases breath methane and serum acetate concentrations in human subjects

Abstract

Guar and psyllium are fermented by human fecal bacteria in vitro. To see if they were fermented in vivo, eight subjects were studied over 3 separate days, in random order, while eating a polysaccharide-free diet. Twenty grams guar or psyllium, taken at breakfast, had no effect on breath hydrogen levels over 14 h. Mean breath methane and serum acetate concentrations after guar, 37 +/- 1 ppm and 93 +/- 6 mumol/L, respectively, were significantly greater than after control, 20 +/- 2 ppm (P less than 0.05) and 62 +/- 4 mumol/L (P less than 0.01), and psyllium, 20 +/- 2 ppm (P less than 0.05) and 78 +/- 6 mumol/L (P less than 0.05). Serum acetate increased after guar (area under curve 193 +/- 56 mumol.h/L; P less than 0.02) but decreased after psyllium and control. We conclude that guar is fermented in the human colon, producing rises in breath methane and serum acetate but not hydrogen. Although psyllium had no effect on hydrogen, methane, or acetate, this does not prove that it is not fermented.

Starch-entrapped microsphere fibers improve bowel habit but do not exhibit prebiotic capacity in those with unsatisfactory bowel habits: a phase I, randomized, double-blind, controlled human trial

“…Salyers et al suggests that psyllium may be fermentable due to the presence of arabinoxylans [32], but the complex nature of these highly branched arabinoxylans [33] may cause incomplete fermentation of psyllium with little or no effect on SCFA production. The lack of fermentibility or incomplete and limited fermentibility of psyllium is supported by our findings as well as prior studies in humans, in which intestinal gas is not increased with psyllium intake, indicating a lack of fermentable properties [6,34,35]. It should, however, be noted that our findings cannot definitely exclude fermentation capacity of psyllium or SM fiber because: (1) SCFA measurements are highly variable, and stool SCFA may not reflect true SCFA production in the intestine [36], and (2) as dietary intake can have strong short-term influences on microbiota [37], and not recording dietary intake the day before stool collection limited the ability to adjust for the influence of dietary intake on microbiota and SCFA.…”

Low‐dose acarbose does not delay digestion of starch but reduces its bioavailability

“…Anchour et al [21] did not observe any hydrogen production after the ingestion of partly digestible starch in the 8-h study period. In addition, fermentation of guar gum, a dietary fibre, did not result in an increase of breath hydrogen despite increased serum acetate concentrations [34]. These observations fit with the general assumption that colonic fermentation of carbohydrates is not always reflected in increased levels of hydrogen in the breath and that this might depend on the type of carbohydrate as well as on the length of the study period.…”

Digestibility and bulking effect of ispaghula husks in healthy humans.

“…The gases excreted by the rectum during these periods were not significantly different as regards total volume and composition, except for hydrogen, whose excretion was lower during the ispaghula period (Fig 1). 14 (2) 16 (2) 0-20 Nitrogen g/day 3-8 (0-7) 4-3 (0-5) 0-25 Ammonia mg/day 33 (3) 34 (4) 0-25…”