Dietary fibres and gut microbiome response in obese subjects

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Obesity and its associated metabolic diseases are closely linked with the gut microbiome which is significantly affected by the amount and type of dietary fibre consumed. Reviews have identified broad effects on the gut microbiome with consumption of dietary fibre, but recognise that differentiation between the effects of individual fibres is required. Although fibre is referred to as a single entity in nutrient reference values and other dietary guidance systems, fibres vary significantly in chemical composition and their physico-chemical properties in turn affect their physiological actions. This research will investigate these fibres individually in order to enhance understanding of their influence in the relationship between obesity and the gut microbiome. This pilot project will be of crossover design with randomised order of dietary intervention in up to 20 obese subjects with anthropometry indicating metabolic risk (BMI >30 kg m-2 and waist circumference indicating metabolic risk). Four separate dietary interventions will occur, each of 3 weeks (including a low fibre control, two moderate fibre cereals- sorghum and oats and a high fibre cereal- oats) and there will be a 3-week washout between test phases. We will measure effects of increased cereal fibre intake and of different cereal types, on the microbiome, body weight, percent body fat and serum levels of short chain fatty acids (SCFA) and lipopolysaccharides (LPS). SCFA levels will be modulated (higher levels of some SCFA modulated by the type of fibre) by changes in dietary fibre intake and previous research demonstrates that SCFA are part of the mechanism by which metabolic outcomes are improved. The LPS will act as a marker of toxicity which we would expect to decrease with improved diet. Using microbiome changes as the primary outcome will provide insight for ongoing studies to determine doses of fibre and types of fibre that may have positive benefits on health outcomes due to a mechanism involving the microbiome. We expect beneficial effect of increased dietary fibre intake and reduction of aversive effects associated with obesity. We propose that positive changes in the gut-microbiome can be detected after relatively short periods of time and that change is related to the type of fibre increased in the diet, not just the amount of dietary fibre. We hypothesise that this mechanism is associated with changes in SCFA and LPS (which has been linked with positive health outcomes).

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