Abstract
The aim of this study was to investigate how physico-chemical properties of two dietary fibres, guar gum and pectin, affected weight gain, adiposity, lipid metabolism, short-chain fatty acid (SCFA) profiles and the gut microbiota in male Wistar rats fed either low- or high-fat diets for three weeks. Both pectin and guar gum reduced weight gain, adiposity, liver fat and blood glucose levels in rats fed a high-fat diet. Methoxylation degree of pectin (low, LM and high (HM)) and viscosity of guar gum (low, medium or high) resulted in different effects in the rats, where total blood and caecal amounts of SCFA were increased with guar gum (all viscosities) and with high methoxylated (HM) pectin. However, only guar gum with medium and high viscosity increased the levels of butyric acid in caecum and blood. Both pectin and guar gum reduced cholesterol, liver steatosis and blood glucose levels, but to varying extent depending on the degree of methoxylation and viscosity of the fibres. The medium viscosity guar gum was the most effective preparation for prevention of diet-induced hyperlipidaemia and liver steatosis. Caecal abundance of Akkermansia was increased with high-fat feeding and with HM pectin and guar gum of all viscosities tested. Moreover, guar gum had distinct bifidogenic effects independent of viscosity, increasing the caecal abundance of Bifidobacterium ten-fold. In conclusion, by tailoring the viscosity and possibly also the degree of methoxylation of dietary fibre, metabolic effects may be optimized, through a targeted modulation of the gut microbiota and its metabolites.
Highlights
Dietary fibres are degraded by the gut microbiota in the colon, giving rise to short-chain fatty acids (SCFA) that can be utilized by colonocytes as energy, absorbed into the systemic circulation or excreted in faeces
The relative fluidity measurement showed that the high viscosity guar gum needed 237 s to travel 10 cm, while medium and low viscosity required 9 and 1 s, respectively (Table 3)
The degree of methoxylation and viscosity of dietary fibres was of importance for metabolic effects and gave rise to distinct SCFA profiles as well as specific alterations in the gut microbiota
Summary
Dietary fibres are degraded by the gut microbiota in the colon, giving rise to short-chain fatty acids (SCFA) that can be utilized by colonocytes as energy, absorbed into the systemic circulation or excreted in faeces. It has been established that ingestion of dietary fibres can improve the metabolic profile in humans and supplementation of SCFA to high-fat diet-fed rodents can reduce weight gain [1]. A high intake of dietary fat can induce low-grade systemic inflammation as well as insulin resistance in animal models [3], both factors are key aspects of the metabolic syndrome. Soluble fibre administration in the form of apple pectin, cocoa fibre or β-glucan was able to reduce inflammatory markers and oxidative stress in Zucker rats fed a high-fat diet [4]. A recent study evaluated effects of two highly viscous fibres (hydroxypropyl methylcellulose (HPMC) and guar gum) on adiposity and liver steatosis in high-fat-fed rats and found that both fibres reduced weight gain, fat mass and liver steatosis [5]. The authors emphasized that both the non-fermentable HPMC fibre and the fermentable guar gum reduced adiposity and hepatic steatosis [5], illustrating the importance of viscosity, and not the degree of fermentation, for metabolic effects of fibres
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