Studies in rats and man have shown that polydextrose is partially fermented in the large intestine (18-21, 32). Because not all fibers are degraded equally by bacteria, a range of 0 (nonfermentable, insoluble) to 4.0 (fermentable, soluble) kcal/g have been used for these fibers unless proven otherwise. As previously described, polydextrose has been determined to be 1 kcal/g. Many fibers can be fermented by bacteria in the large intestine to produce hydrogen, methane, carbon dioxide and SCFA (also referred to as volatile fatty acids, VFA). The SCFA are rapidly absorbed from the gastrointestinal tract through the hepatic portal vein and contribute to the energy balance of the body. These contributions include inhibition of hepatic cholesterol synthesis by propionate (33) and aptosis of cancer cells by butyrate (34,35). Qualitative measurement of SCFA was conducted in PDX studies (7) and revealed typical profiles of acetic, butyric and propionic acids. Of the total radioactivity recovered, 17% was from volatile fatty acids. A recent study (36) measured SCFA production from fermentation of 17 carbohydrates by slurries of mixed fecal bacteria. Polydextrose was found to have a molar ratio of acetate: propionate: butyrate of 61: 25: 14. Only 2 carbohydrates provided a higher proportion of propionate and only 3 provided a higher proportion of butyrate. Harada et al. (37) showed, in rats, that SCFA production from polydextrose increased epithelial cell turnover. This positive effect was more pronounced with polydextrose than with pectin.
Polydextrose causes a significant decrease in the pH of duodenal juices. Intestinal infusion of polydextrose (7) resulted in a drop of pH from 7.24 ± 0.45
to 6.44 ± 0.35 after 150 minutes (p < .05). Endo et al. (32) found a similar pH "S
drop. This change can improve the composition of gut microflora by promoting g growth of specific beneficial bacterial strains such as Bacteroides sp. (personal j communication, Carmen, R.J., Techlabs, Virginia) or diminishing detrimental -a bacteria such as Closridium perfringens. Polydextrose was found in one study ^
to significantly increase Bacteroides sp. (36), and in another study to diminish
Clostridium perfringens (32). The latter study also found that polydextrose re- |
duced the levels of certain putrefactive/carcinogenic substances (indole and p-cresol) produced by bacterial fermentation.
These studies show that polydextrose is fermented in a similar way to other fibers, and even has advantages over some (e.g., butyrate/propionate production, beneficial bacteria).
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