Long-term intake of a high prebiotic fiber diet but not high protein reduces metabolic risk after a high fat challenge and uniquely alters gut microbiota and hepatic gene expression.

A mismatch between early developmental diet and adulthood may increase obesity risk. Our objective was to determine the effects of re-matching rats to their weaning diets high in protein or fiber after transient high-fat/high-sucrose challenge in adulthood. We hypothesize that a long-term high fiber diet will be associated with a gut microbiota and hepatic gene expression reflective of reduced adiposity. Wistar rat pups were fed a control (C), high prebiotic fiber (HF), or high protein (HP) diet from 3-15 weeks of age; a high-fat/high-sucrose diet from 15-21 weeks; their respective C, HF, or HP diets from 21-25 weeks. Gut microbiota of cecal contents and hepatic gene expression were measured when rats were terminated at 25 weeks of age. HF rats had higher total bacteria, bifidobacteria and Bacteroides/Prevotella spp than C and HP at 25 weeks (P < 0.05). Firmicutes, especially Clostridium leptum, decreased in HF compared to C and HP (P < .05). The ratio of Firmicutes:Bacteroidetes was markedly lower in HF versus C and HP at 25 weeks (P < .05). HF decreased hepatic cholesterol content compared to HP and C at 25 weeks. HF and HP increased 3-hydroxy-3-methylglutaryl-CoA reductase mRNA and decreased lecithin-cholesterol acyltransferase mRNA compared to C (P < .05). In conclusion, re-matching rats to a HF but not HP diet attenuated the typical increase in Firmicutes:Bacteroidetes ratio associated with consumption of a high fat diet. Lower hepatic cholesterol with long-term HF diet intake may be related to alterations in gut microbiota and hepatic lipid metabolism.

Combined effects of oligofructose and Bifidobacterium animalis on gut microbiota and glycemia in obese rats.

OBJECTIVE: Prebiotics and probiotics may be able to modify an obesity-associated gut microbiota. The aim of this study was to examine the individual and combined effects of the prebiotic oligofructose (OFS) and the probiotic Bifidobacterium animalis subsp. lactis BB-12 (BB-12) on gut microbiota and host metabolism in obese rats. METHODS: Adult male, diet-induced obese Sprague Dawley rats were randomized to: (1) Control (C); (2) 10% OFS; (3) BB-12; (4) OFS + BB-12 for 8 weeks (n = 9-10 rats/group). Body composition, glycemia, gut permeability, satiety hormones, cytokines, and gut microbiota were examined. RESULTS: Prebiotic, but not probiotic reduced energy intake, weight gain, and fat mass (P < 0.01). OFS, BB-12, and the combined OFS + BB-12 improved glycemia (P < 0.05). Individually, OFS and BB-12 reduced insulin levels (P < 0.05). Portal GLP-1 was increased with OFS, whereas probiotic increased GLP-2 (P < 0.05). There was a marked increase in bifidobacteria and lactobacilli (P < 0.01) with OFS that was not observed with probiotic alone. CONCLUSIONS: The impact of prebiotic intake on body composition and gut microbiota was of greater magnitude than the probiotic BB-12. Despite this, an improvement in glucose AUC with both prebiotic or probiotic demonstrates the beneficial role of each of these "biotic" agents in glycemic control.

Dietary leucine improves whole-body insulin sensitivity independent of body fat in diet-induced obese Sprague-Dawley rats.

Dairy foods and dietary calcium (Ca) are potential regulators of body weight and insulin sensitivity. The specific components of dairy responsible for these actions are not known but may include leucine. Our objective was to determine the effect of dietary protein (casein, skim milk or leucine) and Ca level [low, 0.67% (LC) or high, 2.4% (HC)] on adiposity and insulin sensitivity. Obesity was induced in Sprague-Dawley rats with a 6-week period of high-fat/high-sucrose (HFHS) diet intake. Rats were randomly assigned to one of six HFHS diets for 8 weeks where dietary protein was provided as casein, skim milk or casein enriched with leucine, and contained either LC or HC. Body composition via dual-energy x-ray absorptiometry and insulin sensitivity via euglycemic-hyperinsulinemic clamp were measured. Microarray was used to assess gene expression in liver and skeletal muscle. Rats fed leucine had greater insulin sensitivity than those fed casein or skim milk (P<.05). Dietary protein differentially regulated hepatic and skeletal muscle genes associated with insulin, peroxisome proliferator-activated receptor and mammalian target of rapamycin pathways. Specifically, two key genes responsible for insulin sensitivity, hepatic insulin receptor substrate (IRS) and protein kinase B (Akt), were altered in hepatic tissue in response to leucine. Rats fed skim milk and leucine diets had lower body weight compared to those fed casein (P<.05). HC reduced fat mass compared to LC (P<.05). While skim milk and leucine both reduced fat mass, only leucine improved insulin sensitivity compared to casein. Differential expression of genes such as IRS and Akt may be responsible for changes in insulin sensitivity in obese rats.

Prebiotic fiber increases hepatic acetyl CoA carboxylase phosphorylation and suppresses glucose-dependent insulinotropic polypeptide secretion more effectively when used with metformin in obese rats.

Independently, metformin (MET) and the prebiotic, oligofructose (OFS), have been shown to increase glucagon-like peptide (GLP-1) secretion. Our objective was to determine whether using OFS as an adjunct with MET augments GLP-1 secretion in obese rats. Male, diet-induced obese Sprague Dawley rats were randomized to: 1) high-fat/-sucrose diet [HFHS; control (C); 20% fat, 50% sucrose wt:wt]; 2) HFHS+10% OFS (OFS); 3) HFHS + MET [300 mg/kg/d (MET)]; 4) HFHS+10% OFS+MET (OFS+MET). Body composition, glycemia, satiety hormones, and mechanisms related to dipeptidyl peptidase 4 (DPP4) activity in plasma, hepatic AMP-activated protein kinase (AMPK; Western blots), and gut microbiota (qPCR) were examined. Direct effects of MET and SCFA were examined in human enteroendocrine cells. The interaction between OFS and MET affected fat mass, hepatic TG, secretion of glucose-dependent insulinotropic polypeptide (GIP) and leptin, and AMPKα2 mRNA and phosphorylated acetyl CoA carboxylase (pACC) levels (P < 0.05). Combined, OFS and MET reduced GIP secretion to a greater extent than either treatment alone (P < 0.05). The hepatic pACC level was increased by OFS+MET by at least 50% above all other treatments, which did not differ from each other (P < 0.05). OFS decreased plasma DPP4 activity (P < 0.001). Cecal Bifidobacteria (P < 0.001) were markedly increased and C. leptum decreased (P < 0.001) with OFS consumption. In human enteroendocrine cells, the interaction between MET and SCFA affected GLP-1 secretion (P < 0.04) but was not associated with higher GLP-1 than the highest individual doses. In conclusion, the combined actions of OFS and MET were associated with important interaction effects that have the potential to improve metabolic outcomes associated with obesity.