Impact of dietary protein quantity on the non-dysbiotic human microbiome: a controlled feeding study.

The gut microbiome plays an essential role in human health, and alterations in its composition have been associated with a range of gastrointestinal and metabolic disorders. Diet is one of the most important modifiable factors influencing the gut microbiome, with dietary protein known to affect microbial composition and metabolic activity. However, the impact of varying levels of dietary protein on the human gut microbiome remains incompletely understood. This controlled crossover feeding study examined whether diets providing 10% versus 25% of total energy intake from protein alter stool microbiome profiles in healthy adults. Ten participants, four men and six women aged 22–34 years, completed a controlled crossover feeding trial provisioned by the Bionutrition Unit of the Clinical & Translational Research Center at Oregon Health & Science University. Each diet phase consisted of a 3-day run in diet (18% protein) followed by either a 10% protein (lower-protein) or a 25% protein (higher-protein) diet for 7 days in a randomized order, and then, after a washout period, the run in diet followed by the alternate dietary intervention. Anthropometric measurements, dietary tolerance, diet satisfaction, and stool samples for microbiome 16 S rRNA gene sequencing and short chain fatty acids (SCFA), analysis were collected at 5 time points throughout the study. Body mass index was lower after than before the higher-protein diet (p < 0.01). Minor dietary tolerance symptoms included constipation in one participant on the higher-protein diet, mild discomfort in three participants, and fatigue in seven participants on the lower-protein diet. Diet satisfaction was similar (p = 0.28). Stool microbiome composition varied more by individual (57.8%) than by diet (3.5%). No significant changes in dysbiosis scores (p = 0.68), microbiome diversity (p > 0.05), or SCFA concentrations (p > 0.05) were observed. Short-term consumption of dietary protein at 10% or 25% of total energy intake did not result in significant differences in microbiome diversity or SCFA concentrations. This observation may be due in part to the short duration of the study intervention, the subjects’ identity factors, and the different sources of protein in the two intervention diets.