Resistant starch is a name given to a group of foodstuffs that are classified as dietary fibre but are known to be fermentable in the gut. While previously it was thought that dietary fibres were not digested and absorbed in many mammals including humans, more recently evidence has started to emerge that shows that they can be readily fermented in the guts of most mammals, where they produce significant absorbable energy. Much of this energy may come from short chain fatty acids such as acetate, butyrate and propionate, products of bacterial fermentation of resistant starch. Another function of these short chain fatty acids may be as signal molecules. Evidence suggest that short chain fatty acids may induce changes in the gut physiology of host animals that consume resistant starch through a process of cell recognition and induced cellular changes. Evidence suggests that once absorbed, short chain fatty acids also affect liver metabolism, and here may have effect, for example, on cholesterol synthetic rates.
Resistant starch is a subgroup of dietary fibre. Evidence suggests that consuming more fibre in the diet increases the resistant starch delivery to the colon. In humans, gut bacteria convert this resistant starch to short chain fatty acids (such as acetate, butyrate and propionate), and these are absorbed to the circulation. Once absorbed, evidence suggests that they may have the ability to alter the metabolic regulation in the liver. A number of effects are known for short chain fatty acids in the liver including modifications to amino acid and lipid metabolism. This may explain some of the beneficial effects of dietary fibre. Another effect of these short chain fatty acids may be on the gut itself. Evidence suggests that short chain fatty acids act as signal molecules to enterocytes, and this may favourably alter gut function. Short chain fatty acids may also contribute to the energy needs of the individual. Lastly short chain fatty acids may inhibit gut microbes that are detrimental to gut health, and may stimulate growth of favourable strains. High fibre diets may therefore have a profound influence in health in many ways.
The metabolic effects of resistant starch have been investigated in mice. For example, in one study, researchers fed mice an obesogenic diet containing 45 % additional energy content above the daily needs of the mice. This diet was performed in order to model the possible metabolic effects of weight gain and obesity. One group of mice followed this diet while another followed this diet supplemented with 20 % resistant starch. Following 10 weeks of this regimen, the mice consuming the resistant starch had significantly reductions in the production of certain liver amino acids which were not attributable to systemic amino acid uptake, suggesting changes to gene expression. Further there was a significant increase in faecal nitrogen content in the resistant starch treated mice. Taken as a whole these results suggest that resistant starch significantly alters metabolic regulation in the liver of mice, and this supports the contention that products of resistant starch metabolism can affect hepatic metabolism.
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