Beaumont M, et al. - This randomized, double-blind, parallel-design trial aimed to assess the impacts of the quantity and source of dietary protein on microbiota composition, bacterial metabolite production, and consequences for the large intestinal mucosa in humans. The clinical data indicated that the quantity and source of dietary proteins act as regulators of gut microbiota metabolite production and host gene expression in the rectal mucosa, raising new questions about the impact of high-protein diets (HPDs) on the large intestine mucosa homeostasis.

Methods

• This trial was conducted on 38 overweight people who received a 3-wk isocaloric supplementation with casein, soy protein, or maltodextrin as a control.
• After that, fecal and rectal biopsy–associated microbiota composition was analyzed by 16S ribosomal DNA sequencing.
• By 1H-nuclear magnetic resonance, fecal, urinary, and plasma metabolomes were assessed.
• With the use of microarrays, mucosal transcriptome in rectal biopsies was determined.

Results

• The analysis in this study showed that HPDs did not alter the microbiota composition, but induced a shift in bacterial metabolism toward amino acid degradation with different metabolite profiles according to the protein source.
• Findings revealed that correlation analysis identified new potential bacterial taxa involved in amino acid degradation.
• Fecal water cytotoxicity was not modified by HPDs, but was related to a specific microbiota and bacterial metabolite profile.
• It was discovered that casein and soy protein HPDs did not induce inflammation, but differentially modified the expression of genes playing key roles in homeostatic processes in rectal mucosa, such as cell cycle or cell death.