Dietary Fibre - ILSI Argentina

26 Concise Monograph Series
TABLE 10
Variable patterns of short chain fatty acid production from various substrates
Substrates Acetate Propionate Butyrate
Resistant starch 41 21 38
Starch 50 22 29
Oat bran 57 21 23
Wheat bran 57 15 19
Cellulose 61 20 19
Guar gum 59 26 11
Ispaghula (psyllium) 56 26 10
Pectin 75 14 9
Source: Champ et al., 2003
In experiments with specific cell lines, butyrate downregulated
the expression of specific receptors in gut
immune cells and epithelial cells. Short chain fatty acids,
especially butyrate, may also inhibit effects of the proinflammatory
cytokines. Butyrate seems to influence
lymphocyte activation and to inhibit cell proliferation.
This may represent a mechanism whereby the colonic
microflora regulates the host immune response.
However, an abnormal response to butyrate may upset
the homeostasis between the gut immune system and the
colonising bacteria, resulting in epithelial unrest and
inflammation.
Human breast milk contains complex oligosaccharides
that are partially fermented by the resident gut bacteria
to produce short chain fatty acids. These oligosaccharides
are probably responsible for the proliferation of bifido
bacteria and lactobacilli in the gut of the breast-fed infant.
These bacteria appear to be important in the
development and maintenance of intestinal defences
against pathogenic microbial invasion.
Bowel habit
Stool consistency, stool weight and frequency of
defaecation are indicators of gut and specifically of
colonic function. Transit time, the time a substance takes
to pass through the gut, has a wide inter-individual
variation (24-72 hours). The larger part (16-64 hours) of
this time is spent in the large intestine. Dietary fibre
intake is the main determinant of stool weight, which it
increases, and transit time, which it reduces. Both are
important aspects of bowel habit, and seem to play a
role in the prevention of diseases of the large bowel.
As described above fermentable fibres, non-digestible
oligosaccharides and polysaccharides in the colon
increase faecal mass. The short chain fatty acids
generated by fermentation decrease pH within the colon
and, together with the gas produced, encourage
peristalsis. Most studies of the effects of resistant starch
show increases in stool output or bulk. In part, this is
believed to be because the easily fermentable resistant