FULL-FAT AND FAT-FREE DAIRY, WITH AND WITHOUT FERMENTATION, ON GUT MICROBIOME, GUT AND SERUM METABOLOME, AND HOST CARDIOMETABOLIC RISK STATUS

Long-term goal: The longstanding Dietary Guidelines for Americans recommendation to choose fat-free/low-fat dairy in place of full-fat dairy has become highly controversial, as has the potential mitigating effect of fermentation. To address this controversy, our long term goal is to increase insights into cross-talk between host diet, gut microbiome, gut and serum metabolome and indicators of cardiometabolic health. The overarching goal of this proposal is to compare full-fat and non-fat dairy, with and without fermentation, on cardiometabolic risk factors and determine if differences are mediated by functional alterations in gut microbiome and derived metabolites. To accomplish this goal we propose to conduct a randomized-controlled cross-over trial to compare the effect of consuming two servings per day of full-fat (bovine) dairy (milk), fat-free dairy (milk), full-fat fermented dairy (yogurt), and fat-free fermented dairy (yogurt) to address the following objectives.Objective 1. Determine effect of dairy fat in milk, with and without fermentation, on fecal microbiome composition, function and diversity, and measures of gut barrier integrity.Hypothesis 1: Unfermented full-fat, compared to unfermented fat-free milk, will result in (i) lower microbial diversity, (ii) higher abundance of bile salt hydrolase (e.g., Lactobacillus, Bifidobacterium, Enterococcus, Clostridium spp. and Bacteroides) and lipophilic (e.g. Eubacterium coprostanoligenes, Bacteroides intestinalis and Faecalibacterium prausnitzii) microbiota, (iii) lower abundance of butyrate producing microbiota (e.g., Faecalibacterium prausnitzii and Clostridium leptum of the family Ruminococcaceae, and Eubacterium rectale, Roseburia spp. of the family Lachnospiraceae, Eubacterium hallii and Anaerostipes spp) and proteolytic microbiota (e.g., Lactococcus lactis, Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus gener), and (iv) lower gut barrier integrity (higher lipopolysaccharide [LPS] and lipopolysaccharide binding protein [LBP] concentrations). These alterations will be favorably modulated by fermentation.Objective 2. Determine the effects of dairy fat in milk, with and without fermentation, on fecal and serum metabolomes, and CMRF.Hypothesis 2: Full-fat, compared to fat-free, unfermented milk will (i) increase fecal trimethylamine (TMA) and (serum trimethylamine oxide [TMAO]), 1° and 2° bile acids, com-plex lipids (cholesteryl ester, phosphatidylcholine, lysophosphatidylcholine, ceramides, sphingomyelins, diglycerides/triglycerides]), and decrease branched chain amino acids [BCAA] and short chain fatty acids [SCFA]), and (ii) these responses will be associated with higher fasting serum insulin, low density lipoprotein (LDL)-cholesterol and triglyceride concentrations, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), systolic and diastolic blood pressures, and inflammatory biomarkers (high sensitivity C-reactive protein [hsCRP] and tumor necrosis factor alpha [TNFα]) concentrations. These alterations will be favorably modulated by fermentation.Objective 3. Determine associations between gut microbiome with the fecal metabolome, serum metabolome and CMRF using bioinformatics/integrative pathway analysis to identify biological pathways modulated by dairy fat and fermentation.Hypothesis 3: The differential effects of full-fat and fat-free fermented and unfermented dairy on CMRF risk factors will be mediated by gut microbiota and derived metabolites on host glucose, amino acid, lipid and inflammatory metabolic pathways.Exploratory Objective. Assess the effect of sex as a biological variable on responses to the dietary interventions.Exploratory Hypothesis: Women will have higher microbial composition, diversity and functional rich-ness than men.