The research published in the British Journal of Nutrition provides further understanding on the role of non-digestible carbohydrates.
Non-digestible carbohydrates such as polydextrose (PD) and resistant maltodextrin (RMD) are already added to processed foods as a low-energy bulking agent and have been reported to help prevent metabolic syndrome and lifestyle related diseases. Earlier this year the European Food Safety Authority (EFSA) backed claims for favourable glycaemic response when sugars are replaced by non-digestible carbohydrates.
However, resistant glucan (RG) and hydrogenated resistant glucan (HRG) are newly developed non-digestible carbohydrates for which metabolic pathways and physiological function has yet to be examined.
Tsuneyuki Oku and colleagues from three Japanese universities set out to fill in those knowledge gaps and hypothesised that RG and HRG may act in the same way as PD and RMD, because of similar biochemical structural components.
They conducted a series of in vitro, in vivo and animal experiments to discover the effects and digestibility of the newer dietary fibres compared to those that were already being added to foods.
They also observed physical effects on rats raised on a diet containing RG or HRG for four weeks noting growth rates, gastrointestinal tract and other organ weights, blood biochemical parameters and faecal shape.
Rats being fed the experimental diet containing RG or HRG had loose stools throughout the period, but it didn’t affect their growth or development.
Rats fed diets with RMD also had loose stools, and those fed fructooligosaccharides (FOS) recovered from this digestive disturbance after the first week and thereafter had normal stools. Purified RG was found to be the most resistant to digestion and fermentation, with results suggesting 99% went undigested.
The authors concluded:"RG and HRG contained small amounts of digestible and non-digestible oligosaccharides and large amounts of glucose polymers that were hardly hydrolysed by α-amylase and small intestinal enzymes, and had no harmful effects on the growth and development of rats. Therefore, RG and HRG could be used as new dietary fibre materials."
Next steps in human research
The authors considered why the FOS-fed rats recovered from loose stools quickly compared to those on the RG and HRG diet: "One explanation for this is that intestinal microbes that readily use non-digestible oligosaccharides increased spontaneously and quickly used the oligosaccharides. In the present study, loose stools following feeding by RG and HRG remained until the end of the experiment.
"These results demonstrate that intestinal microbes that readily use RG and HRG did not proliferate. Indirectly, this supports the view that RG and HRG are resistant to fermentation by intestinal microbes. If RG and HRG are fermented spontaneously by intestinal microbes, hydrogen would be produced and excreted. Therefore, we would like to measure hydrogen excretion in further experiments using rats and healthy human subjects."
Source: British Journal of Nutrition
Published online ahead of print, doi: 10.1017/S0007114515003311
“Digestibility of new dietary fibre materials, resistant glucan and hydrogenated resistant glucan in rats and humans, and the physical effects in rats”
Authors: T. Oku et al