Dietary Fiber Effects on the Microbiome and Satiety
Trial Parameters
Eligibility Fast-Check
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Brief Summary
Strong evidence supports the association between high fiber (HiFi) diets (e.g. legumes, nuts, vegetables) and a reduced risk for chronic conditions such as cardiovascular disease (CVD), type 2 diabetes and some forms of cancer. However, the current U.S. average consumption of dietary fiber of 17g/day is significantly below the recommendation level of 25g/d for women and 38g/d for men. Furthermore, fiber fermentation to produce short chain fatty acid (SCFA) products and alterations in microbial composition and activity may be mechanisms linking a HiFi diet to improved health. Importantly, much of the data, including findings supporting a beneficial role of SCFA have been derived from animal studies. Human studies are now needed to advance the understanding of the translational significance of rodent studies and the potential benefit of fiber on microbial metabolites and cardiometabolic health, glucose regulation, appetite and satiety. The central hypothesis is that that the mechanisms by which dietary fiber provides metabolic benefit include direct physical effects in the upper gastrointestinal tract to slow nutrient absorption, and indirect effects to reduce food intake mediated by SCFA-induced secretion of intestinal hormones resulting in increased satiety. Design: Using fiber derived from peas, Aim 1 will test the effect of a HiFi diet on appetite, satiety, and cardiometabolic health and whether elevated SCFA concentration mediates improved satiety in 44 overweight/obese subjects randomly assigned to receive either a high fiber or a low fiber dietary intervention for four weeks in a parallel arm-repeated measures design. Aim 2 will quantitate the changes in microbial composition and colonic SCFA production rate during HiFi feeding and whether any changes are potential mediators of observed benefits on satiety and cardiometabolic risk factors in 26 subjects assigned to receive a high fiber intervention for 3 weeks in a repeated measures design. Relevance: These studies will significantly expand the understanding of mechanisms by which dietary fiber improves satiety and cardiometabolic health in humans.
Eligibility Criteria
Inclusion Criteria: * Men and women (premenopausal only) * Age 20-55y (Aim 1); 45-55y (Aim 2) * BMI ≥25 or ≤35 kg/m2 (Aim 1); ≥25 or ≤40 (Aim 2) * Weight stable (no fluctuations in body weight of greater than 4 kg in the last 3 months) * Willing to consume a research diet * Willing to provide blood and fecal samples * At least one characteristic of the metabolic syndrome (but not diabetic) 1\. A large waistline: 35 inches or more for women 40 inches or more for men 2. High triglycerides: 150 mg/dL or higher 3. Low HDLc level: \<50 mg/dL for women \<40 mg/dL for men 4. High blood pressure ≥130/85 mmHg 5. Fasting blood sugar ≥100 mg/dL * Pre-diabetes acceptable (glucose \<125 mg/dL or HbA1c \<6.5%) * Stably treated with statin drugs, anti-hypertensives, and anti-depressants. These are acceptable as long as the drug category does not alter appetite, body weight, or the microbiome (if known) Exclusion Criteria: * Pregnant or lactating * Postmenopausal (evidence suggests an interplay betwee