Degree of Dietary Refinement Alters Apparent Gut Permeability
Authors: Price Tara R. , Walzem Rosemary L. 
Published: June 2021

Previous studies in our lab showed less refined diets reduced gut permeability (GI‐p) as assessed by 4hr plasma FITC‐dextran (FITC‐d) concentration in conjunction with reduced adiposity. To determine if degree of dietary refinement altered gut health and lipoprotein biology, we conducted a 14 week feeding trial in which weanling C57Bl/6 mice (n=15/diet) were fed one of four diets differing in dietary protein source (soy or milk protein) and degree of refinement. All diets provided 20%EN PRO, 30% EN fat, and 50% EN CHO. Purified diets contained either isolated soy protein (ISP) or dried whole milk powder (DWMP) as the protein source, while non‐purified diets contained either soybean meal (SPC), or dried whole milk powder (DMC) as protein sources. Purified diets contained 14% neutral detergent fiber (NDF) as cellulose, while non‐purified soy and milk protein diets provided 11.4% and 8.4% NDF, respectively, from wheat middlings, corn, corn gluten meal and soybean meal (SPC diet). All diets provided an average 3.3 %N as analyzed by Rapid N‐cube (Elementar, Germany). Mice fed purified diets were heavier than those fed non‐purified diets, with ISP‐fed mice being heaviest (p<0.033). Mice consumed similar amounts of energy in the different diets. Fecal %N was significantly increased in the non‐purified SPC‐ and DMC‐fed mice (2.99%, 2.98% respectively), being almost double that of ISP or DWMP (1.52%, 1.76%; p<0.000). At week 12, apparent GI‐p was highest in ISP‐fed mice (12.8 ng/mL), being significantly increased over DMC (8.96 ng/mL; p<0.02). Purified diet feeding resulted in increased apparent GI‐p, regardless of protein source (12.1 ng/mL vs. 9.56 ng/mL; p<0.004). Whole‐gut transit time averaged 2.5 hours longer for mice fed purified diets (6.6 hrs vs. 4.1 hrs, p<0.0001). Division of the value of 4 h FITC concentration used as the GI‐p index, by gut transit time, abolished differences due to diet purification; raising the possibility, that gut permeability per se did not differ among dietary groups. Consistent with this, cytokines (TNF‐a, IL‐1b, IL‐6, IL‐10) measured in whole blood and intestine explants were generally low and non‐indicative of either tissue or systemic inflammation. Density distributions of NBD‐stained lipoproteins showed that diets containing milk protein increased lipoproteins of d < 1.019 g/mL (TRL) (3.44% v. 5.4%) and HDL (d = 1.063 – 1.18 g/mL) (64.2% v. 60.6%) and decreased LDL (d=1.019–1.063 g/mL) (30.5% v. 36.0%, p<0.04). Compared to all other diets, mice fed ISP had a 30% increase in small dense LDL (d=1.05 – 1.063 g/mL) (p<0.000) and a ~ 4.0% decrease in HDL‐2b (d = 1.063–1.091 g/mL) (p<0.000). Increasing FITC‐d concentrations in plasma were significantly associated with decreases in %TRL (p<0.0127). In diets providing macronutrient distributions following the USDA's Dietary Guidelines for Americans, degree of purification seemingly has a greater effect on GI‐P, motility, and nitrogen utilization than protein source, while milk protein‐containing diets resulted in improved lipoprotein profiles regardless of purification.Support or Funding InformationThis project was supported in part by Texas AgriLife Research [Project 8738, R.L.W.)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.