Determining the true digestibility of plant-based proteins and their effect on obesity, NAFLD, and the gut microbiome

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Determining the true digestibility of plant-based proteins and their effect on obesity, NAFLD, and the gut microbiome

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Introduction: The Protein Digestibility Amino Acid Corrected Score (PDCAAS) is the current FDA standard for determining protein quality. As more isolated plant proteins come onto the marketplace, the database of current PDCAAS values for these plant proteins needs to be expanded. There is also a need to understand more the health effects of isolated plant proteins. A serious and growing health issue is non-alcoholic fatty liver disease (NAFLD), for which no pharmacological intervention exists to treat it. Here, we determined PDCAAS values for wild rice, brown rice, pea flour, and two different pea flour protein isolates. In addition, we report the effect of feeding wild rice, brown rice, and pea flour on obesity, liver lipids, an early stage of NAFLD, and the gut microbiome. Methods: Male Wistar rats (n=8 per group) were fed a diet of either casein (control diet, CC), wild rice (WR), brown rice (BR), pea flour (PF), pH precipitated pea protein isolate (PPI pH), salt solubilized pea protein isolate (PPI salt), or protein-free for 2-10 weeks. For the first 2 weeks of feeding the diets, which was for PDCAAS determination, each diet except the protein-free contained either 10% protein or as close as possible to it. After 2 weeks the PPI pH, PPI salt, and protein-free rats were euthanized, and the remaining rats were switched to a high fat background diet (High Fat Diet; HFD) to induce NAFLD. The experimental diets contained 40% by weight of either wild rice, brown rice, or pea flour and fed for 8 more weeks. Cecal contents, livers, and epididymal fat pads were harvested. Microbiome analysis of cecal contents was conducted by 16S sequencing. Results: The PDCAAS values for the plant proteins tested are 0.61 for BR, 0.60 for WR, 0.73 for PF, 0.61 for PPI pH, and 0.70 for PPI salt. In the HFD trial, both WR and BR significantly reduced total liver lipids compared to CC (p < 0.0001). However, epididymal fat pad weight was not reduced in either of the rice groups compared to CC (p > 0.05). Serum cholesterol was also reduced in WR compared to CC (p < 0.0188). Additionally, p-AMPK/AMPK and ACC/pACC activation was not seen in the HFD trial (p > 0.05). In the HFD trial, microbiome analysis showed that the beta-diversity measure of community dissimilarity indicated that WR had a significantly different microbial profile compared to the animals fed the CC diet (p < 0.003) while BR had an increased abundance of lactobacillus (p < 0.03) compared to animals fed the CC diet. Conclusions: Pea flour had the highest PDCAAS values among the plant protein sources. Wild rice feeding, but not pea flour feeding, reduced fatty liver and altered the gut microbiome. Wild rice should be further explored as a dietary approach to prevent development of non-alcoholic fatty liver disease (NAFLD), and to investigate whether hepatic lipid reductions are mediated by changes in the gut microbiome.


University of Minnesota M.S. thesis. 2022. Major: Nutrition. Advisor: Daniel Gallaher. 1 computer file (PDF); 141 pages.

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Eggers, Joseph. (2022). Determining the true digestibility of plant-based proteins and their effect on obesity, NAFLD, and the gut microbiome. Retrieved from the University Digital Conservancy,

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