Interactions between Dietary Protein and Vegetable Fiber via the Gut Microbiota Are Associated with Cecal Fermentation Profiles and Immunoglobulin A Responses in Rats.

BACKGROUND

Influence of dietary protein and its interaction with dietary fiber (DF) on gut microbiota, fermentation, and host immunity, particularly immunoglobulin A (IgA) responses, is not fully understood.

OBJECTIVES

This study examined how gut microbiota adapt to dietary protein, subsequently influencing fermentation profiles and IgA responses, and how these effects are modulated by coingestion of vegetable fiber (VF).

METHODS

Male Wistar rats (5 wk old) were fed one of 6 diets varying in protein (casein, soy, and egg white) and DF (cellulose, VF) source for 14 d (n = 6/group). Cecal microbial composition, organic acids, ammonia, IgA, and immune-related gene expression as well as fecal IgA were analyzed. Data were analyzed using 2-way or aligned rank transform analysis of variance (ANOVA). Microbiota composition was assessed using permutational multivariate ANOVA and ANOVA-like differential expression tool version 2, and Spearman's rank correlation was applied for microbial co-occurrence network construction and correlation analysis.

RESULTS

Soy protein-VF diet yielded the highest alpha-diversity, whereas egg white protein-VF diet yielded the lowest across multiple indices (P < 0.05). Beta-diversity analysis confirmed distinct clustering among dietary groups (P < 0.001), whereas network analysis showed that protein source affected community structure. Soy protein-VF diet showed an increase in n-butyrate production relative to soy protein-cellulose diet (49.09 compared with 17.28 μmol/cecum, P < 0.05). Egg white protein-cellulose diet showed the highest ammonia production that was suppressed by VF coingestion (155.52 compared with 61.66 μmol/cecum, P < 0.05). Notably, cecal IgA showed a positive correlation with ammonia (ρ = 0.67, P-adj. < 0.01).

CONCLUSIONS

In rats, dietary protein and its interaction with VF are associated with compositionally distinct microbial signatures that influence fermentation profiles and IgA responses in the cecum. These findings highlight the importance of considering protein-fiber combinations when designing dietary interventions to optimize gut health.