Dietary Matrix Alters Fecal Lipids and Lipoprotein Profiles in Healthy C57Bl/6 Mice
Authors: Price Tara R. , Moncada Kristin L. , Blake Amanda , Suchodolski Jan , Walzem Rosemary L. 
Published: June 2021

Plant proteins are oft thought to confer health benefits over animal proteins. In a prior study, lipoprotein profiles improved and body weight gain reduced in mice fed milk protein rather than soy protein fed in a purified diet (PD) matrix. Non‐nutrient components such as fiber can alter macro‐ and micro‐nutrient utilization; this study tested the effect of dietary matrix on lipoprotein profiles, fecal lipids and bile acids. Weanling C57Bl/6 mice (n=15/diet) were fed either PD containing isolated soy protein (ISP) or dried whole milk powder (DWMP) as the protein source, or natural ingredient diets (NID) containing soybean meal (SPC), or dried whole milk powder (DMC) as protein sources in a 14 wk feeding trial. Diets provided 50%EN CHO, 20% PRO, 30% FAT. ISP & DWMP provided 14% neutral detergent fiber primarily from cellulose, while SPC & DMC contained 11.4% and 8.4% NDF, respectively, from wheat mids, corn, corn gluten meal and soybean meal (SPC only). Terminal measures: bodyweight, lipoprotein density distribution (https://doi.org/10.1177/1040638718793677), and fecal fatty acids (FA), sterols, primary (PBA) and secondary (SBA) bile acids by IS‐controlled GC/MS. Values are means with differences tested by one‐way ANOVA and Tukey's HSD. Energy intake was similar among groupsaveraging 12 kcal/day.

Diet
Weight, g
Fatty acids mg/mg feces
Fecal content / 48 hours

Body, final
Feces, 48h
Sterols, mg (%phyto‐)
Bile acids, ug

Primary
Secondary

ISP
35.0a
1.14a
17.6b
2.66c(52.6%)
378b
426a

DWMP
31.9ab
1.22a
14.8b
1.87d(31.7%)
510ab
370ab

SPC
28.8b
0.88b
39.7a
4.82a(68.6%)
398b
295bc

DMC
29.7b
0.66c
31.1a
3.69b(60.1%)
551a
263c

Mice fed ISP & DWMP were heavier than SPC & DMC fed mice (p<0.001). ISP‐fed mice were heaviest (p<0.0002 vs. SPC & DMC). SPC & DMC excreted 46.0 ug fecal FA/mg feces, 3‐fold greater than the 13.5 ug fecal FA/mg feces excreted by ISP&DWMP (p<0.000). Total fecal FA excretion in 48h was ≤ 1 kcal; unable to account for differences in body weight. Total fecal sterol excretion was 1.9‐fold greater in NID vs PD, p<0.0001. Phytosterols comprised a greater fraction of fecal sterols in NID that in PD; soy diets (ISP & SPC) excreted 2.5 and 1.5‐fold more than dairy protein comparators. Zoosterols were increased 17% in NID fed mice (1.49 mg avg) compared to PD mice (1.27 mg avg) and unaffected by phytosterols. Bile acid excretion in DWMP was 9% greater than ISP, and DMC was 17% greater than SPC. Secondary bile acids avg 22.4% lower in mice fed milk‐based diets compared to soy. When expressed as % of total, PBAs were highest in NIDs (61.0 vs 50.7%, p<0.0002), whereas SBAs were lower compared to purified diets (38.3 vs 48.4%, p<0.0002). 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). Carbohydrate refinement has a greater effect fecal lipids than protein source. Milk protein‐containing diets resulted in improved lipoprotein profiles in PD and NID diets.Support or Funding InformationSupported in part by Texas A&M AgriLife Research project 8738 (to R.L.W.)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.