Abstract
Obesity leads to changes in the gut microbial community which contribute to the metabolic dysregulation in obesity. Dietary fat and fiber affect the caloric density of foods. The impact of dietary fat content and fiber type on the microbial community in the hind gut is unknown. Effect of dietary fat level and fiber type on hindgut microbiota and volatile fatty acid (VFA) profiles was investigated. Expression of metabolic marker genes in the gut, adipose tissue and liver was determined. A 2×2 experiment was conducted in pigs fed at two dietary fat levels (5% or 17.5% swine grease) and two fiber types (4% inulin, fermentable fructo-oligosaccharide or 4% solka floc, non-fermentable cellulose). High fat diets (HFD) resulted in a higher (P<0.05) total body weight gain, feed efficiency and back fat accumulation than the low fat diet. Feeding of inulin, but not solka floc, attenuated (P<0.05) the HFD-induced higher body weight gain and fat mass accumulation. Inulin feeding tended to lead to higher total VFA production in the cecum and resulted in a higher (P<0.05) expression of acyl coA oxidase (ACO), a marker of peroxisomal β-oxidation. Inulin feeding also resulted in lower expression of sterol regulatory element binding protein 1c (SREBP-1c), a marker of lipid anabolism. Bacteria community structure characterized by DGGE analysis of PCR amplified 16S rRNA gene fragments showed that inulin feeding resulted in greater bacterial population richness than solka floc feeding. Cluster analysis of pairwise Dice similarity comparisons of the DGGE profiles showed grouping by fiber type but not the level of dietary fat. Canonical correspondence analysis (CCA) of PCR- DGGE profiles showed that inulin feeding negatively correlated with back fat thickness. This study suggests a strong interplay between dietary fat level and fiber type in determining susceptibility to obesity.
Highlights
Recent analysis of the human hindgut microbiome suggests a strong association between microbiome composition and obesity susceptibility [1,2,3]
We observed increased concentrations of volatile fatty acids in the inulin-fed pigs, the extra energy from the VFAs was not high enough to lead to a significant increase in body weight gain, compared with solka floc-fed pigs
Evidence suggests that insoluble fiber induces proliferator-activated receptor gamma coactivator 1alpha (PGC1a) expression, a transcription factor that regulates expression of genes involved in mitochondrial fatty acid oxidation, increasing mitochondrial b-oxidation and reduction in fat mass [30]
Summary
Recent analysis of the human hindgut microbiome suggests a strong association between microbiome composition and obesity susceptibility [1,2,3] These studies suggest that alteration of the gut microbial community could be an approach for obesity prevention and treatment [1]. The pig is an ideal animal for investigating the effect of dietary components on bacterial communities and metabolic changes because of similarities in its dietary requirements, and the anatomy and physiology of its digestive tract with that of humans [2]. Fiber has multiple effects on the body, such as, regulation of host gut bacterial community and hind gut fermentation and health [5,6]. There is a preponderance of evidence on the beneficial effect of dietary fiber on health and metabolic status in humans and animals. The extent to which dietary fiber regulates metabolism beyond the gastrointestinal tract is still unclear
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