The influence of habitual dietary intake on the responsiveness of the gut microbiota to a dietary intervention : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Manawatu, New Zealand
Preliminary evidence suggests that inter-individual variability in gut microbiota response to a dietary intervention is influenced by baseline gut microbiota composition. Differing habitual dietary intakes lead to distinctions in baseline gut microbiota composition making it plausible that habitual dietary intake may also influence gut microbiota response. Prior to conducting this research no studies had been undertaken to determine whether habitual dietary intake has an impact on gut microbiota responsiveness. Therefore, the aim of this research was to investigate the influence habitual dietary intake has on gut microbiota response to a dietary intervention.
Initially, secondary data analysis was conducted to determine whether there was any support for the hypothesis that individuals with differing habitual dietary intakes would have gut microbiota that respond in a distinctive manner to a dietary intervention. The secondary data analysis results demonstrated that dietary groups rich in dietary fibre had the greatest impact on gut microbiota responsiveness. An in vitro three-stage colonic model system study was conducted to determine whether media with differing fermentable carbohydrate (i.e. dietary fibre) contents influenced gut microbiota response to an inulin-type fructan prebiotic. It was demonstrated that differing prebiotic driven changes in organic acids and bacterial taxa occurred between the low (LFC) and high fermentable carbohydrate (HFC) content media. The results of the secondary data analysis and in vitro study provided evidence to suggest that a human intervention study was warranted. A randomised, double-blind, placebo-controlled, cross-over, human intervention study in 34 healthy participants was undertaken to determine whether habitual dietary fibre intake influenced gut microbiota response to an inulin-type fructan prebiotic. The results of the human intervention study demonstrated that the low habitual
dietary fibre (LDF) group harboured gut microbiota that were less responsive to the inulin-type fructan prebiotic than the high habitual dietary fibre (HDF) group.
Future studies which aim to modulate the gut microbiota via dietary change or to determine the prebiotic potential of a novel fermentable substrate should take habitual dietary fibre intakes into consideration when recruiting participants or analysing the data. This will help reduce the confounding influence of inter-individual variability in gut microbiota responsiveness and ensure the true efficacy of a dietary intervention is demonstrated.