Investigating Optimal Propionate Delivery to the Colon Using Stable Isotope Labeling

The role of SCFA in appetite regulation: SCFA have been shown to stimulate PYY and GLP-1 production in animal models and dietary fibre, of which SCFA are the major end products, induce appetite regulation in humans. However the evidence underpinning which dietary fibres induce appetite regulation in humans is very weak because of the difficulty in controlling studies with very high fibre intake. In a recent project funded under the BBSRC DRINC initiative (BB/H004815/1), we have the first direct evidence that SCFA can directly regulate appetite in humans. Prior to this study, in order to achieve production of SCFA to a level, which is high enough to induce appetite-regulating effects, very large amounts of dietary fibre (>25 g/d and up to 40 g/d) are required, and compliance with high fibre diets is poor due to gastrointestinal side effects. Furthermore, supplementing diets with mixed high fibre does not predictably or reliably increase colonic SCFA production or circulating levels of SCFA in all human populations because of the variability in gut microbial activity. Finally, orally administered SCFAs are not palatable and are rapidly absorbed in the small intestine where L cells are sparse. In our studies to date we have focussed on the SCFA propionate because it has the highest affinity for the receptors and is an end product of metabolism in the microbiota and therefore seems the obvious target to manipulate to investigate the effects of SCFA on appetite regulation. To overcome the unpalatably high levels of fermentable dietary fibre needed to significantly increase colonic propionate levels, and the unpredictability in the production of the resulting SCFAs, we have developed and tested a novel delivery system targeting the release of gram quantities of propionate in the proximal colon. We estimate that our delivery system may lead to a 2-8 fold increase in colonic propionate, a level very difficult to achieve through feeding a mixed fermentable fibre diet. This level of propionate production might have been observed in ancestral diets and in parts of rural Africa where dietary fibre intake is very high. We have also demonstrated that delivery system increases plasma propionate levels, reduces food intake in acute studies of appetite, and in a longer term study (24 weeks), positive effects on food intake, body composition, glucose homeostasis, circulating lipids, cholesterol and liver function, liver and visceral fat and weight management were observed. However, in these studies we pragmatically chose an preparation that could be produced at scale. The amount of propionate released can be varied which in itself may affect the rate and amount of propionate released. For an ingredient, with the potential to be incorporated into a wide variety of foodstuffs, we now wish to investigate the optimum delivery system preparation that delivers the maximal propionate dose in the least amount of material.

We plan to use non-invasive, stable isotope labelling methodologies to determine propionate bioavailability from a range of delivery system preparations, in order to determine the optimum preparation for delivering maximal propionate to the proximal colon.