Higher intakes of dietary fiber are protective against obesity. Fermentation of fiber in the gut may
be the mechanism for this protective effect. To evaluate this hypothesis, we fed 22 healthy female
subjects, ages 18 - 40 years, commercially prepared snack bars which contained no fiber, or 10
grams of four different fibers: fructo-oligosaccharide, inulin, soluble corn fiber and resistant starch.
The study consisted of five test visits, separated by at least 1 week. Fasted subjects arrived at the
test center and consumed their breakfast bar. Breath samples were collected from each subject at
baseline and 180 minutes after they consumed snack bars during each study period. Breath
samples were analyzed for breath hydrogen levels as a measure of fiber fermentation in the large
intestine. The hydrogen levels at baseline and 180-minute point were compared for each subject
and each type of fiber. Not all of the fibers showed significant effects on breath hydrogen levels.
There were significant differences of breath hydrogen excretion and fiber digestion between
baseline and 180-minute point for some dietary fibers. Breath hydrogen values were not
significantly different for some fibers. Therefore, not all fibers are equally fermentable in the human
colon. This result claims that all fibers are fermentable in the colon and may therefore affect body
weight are not warranted.
This research was supported by the Undergraduate Research Opportunities Program (UROP) and the Kellogg Company.
Fermentation of Fiber in the Gut: a Mechanism to Explain Fiber’s Protective Role in Weight Control.
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