(LB01-40-26) Starting Point Matters: How Habitual Diet Predicts Both participant[MN1.1] Baseline Microbiome and Participant Response to a Dietary Intervention

Objectives: To determine how participants’ usual (baseline) diets influence their gut microbial community structure at baseline and whether those baseline dietary patterns modify their microbiome response to each diet arm in a cross-over feeding trial.

Methods: EAT-WELL was a randomized, controlled feeding trial where participants (n=20) consumed two controlled diets, one including red and processed meats and one without. Other aspects of the diet were identical. Each diet was consumed for three weeks with a washout period in between. Baseline dietary intake was assessed using 4‑day food records, and stool samples collected at baseline and after each feeding period underwent 16S rRNA sequencing. Alpha and beta diversity were calculated and analyzed using linear mixed models and regression-based kernel association tests adjusted for diet order, age, BMI, and baseline nutrient intake; multivariate analyses with were conducted using MaAsLin2 with CLR‑transformed data.

Results: 18 participants completed the food records. After adjustment, cross‑sectional analyses showed that baseline protein intake was significantly associated with alpha diversity (p < 0.01), and adjusted longitudinal models similarly identified protein as a key predictor of alpha diversity over time (p < 0.01). Beta diversity analyses did not reveal any significant differences. Multivariate taxonomic analysis indicated that the Streptococcaceae and Eggerthellaceae families were upregulated in the diet arm without red and processed meat (q value=0.078).

Conclusions: Participants were habitual meat eaters (mean=1.2 oz/day), and baseline protein intake may have shaped how their microbiome responded to the intervention. The upregulation of Streptococcaceae and Eggerthellaceae in the no‑meat diet arm may reflect microbial shifts triggered by removing a familiar protein source, with individuals consuming more protein at baseline potentially experiencing greater restructuring that allowed opportunistic taxa to expand.

Funding Sources: R21DK128754, P30CA015704

UW Microbial Interactions & Microbiome Center

Secretaría de Ciencia, Humanidades, Tecnología e Innovación (Mexico)