Abstract
Dietary intake of fiber-rich food has been reported to contribute to multiple health benefits. The aim of the current study is to investigate the effects of a diet containing the outer bran fraction of rice (OBFR), which is rich in insoluble fiber, on the intestinal environment and metabolite profiles of rats. Fourteen 8-week-old male Sprague–Dawley rats were divided into a control group and an OBFR group. For a period of 21 days, the control group was fed a control diet, while the OBFR group was fed a diet containing 5% OBFR. Metabolomics analysis revealed drastic changes in the cecal metabolites of the rats fed the OBFR diet. Furthermore, in the plasma and liver tissue, the concentrations of metabolites involved in pyruvate metabolism, the pentose phosphate pathway, gluconeogenesis, or valine, leucine, isoleucine degradation were changed. Concordantly, the OBFR diet increased the expression of genes encoding enzymes involved in these metabolic pathways in the livers of the rats. Collectively, these results suggest that the OBFR diet altered the concentrations of metabolites in the cecal contents, plasma, and liver, and the hepatic gene expressions of rats, and that this may have mainly contributed to carbohydrate metabolism in the liver.
Highlights
Dietary fiber can be classified as insoluble or soluble, depending on its solubility in water
The OBFR diet significantly reduced the digestibilities of crude protein (CP), ether extract (EE), and nitrogen-free extract (NFE) (Table S3)
Given that OBFR is rich in insoluble fiber [16], these results suggest that the OBFR diet reduced feed efficiency by reducing the digestibility of CP, EE, and NFE
Summary
Dietary fiber can be classified as insoluble (cellulose, hemicellulose, and lignin) or soluble (pectin and gum), depending on its solubility in water. It has been well established that dietary fiber contributes to multiple health benefits [1] by reducing caloric absorption [2,3] and increasing the fecal excretion of energy, protein, and fat [1,4]. Ingesting insoluble fiber has been found to reduce energy digestibility, body weight gain, or blood lipid levels in animals, e.g., feeding a dietary fiber-rich by-product of the soy milk industry to healthy rats for 4 weeks showed decreases in weight gain and serum total cholesterol level [5]. We previously found that feeding the outer bran fractions of rice (OBFR) to rats for 3 weeks enhanced fecal lipid excretion, and reduced abdominal lipid accumulation [6]. Eating rice bran can substantially improve bowel movement and fecal excretion [8], and reduce plasma triacylglycerol and Nutrients 2020, 12, 430; doi:10.3390/nu12020430 www.mdpi.com/journal/nutrients
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