Background: Evidence is accumulating that gut bacterial communities modulate the outcome of dietary interventions. Objective: To assess how gut microbial enterotypes correlate with obesity-related outcomes during one month of whole milk consumption. Methods: This post hoc analysis used data from a previously published trial, which included a lead-in phase during which men with abdominal adiposity replaced habitual dairy product consumption with 400 g/day of whole milk for one month. We compared body weight, urinary metabolites, fecal metabolites, and gut microbiome composition and function based on shotgun metagenomic sequencing at the beginning and at the end of the lead-in phase between individuals with the two most prevalent enterotypes, the Bacteroides1 (B1) enterotype (n = 24) and the Ruminococcaceae (R) enterotype (n = 38). Results: Individuals with the B1 enterotype, but not those with the R enterotype, exhibited decreases in body weight and the relative abundance of Streptococcus thermophilus. Multiple linear regression analysis identified enterotype as a strong predictor of body weight change (p = 0.0034). In addition, urinary taurine level change was positively associated with body weight change in B1 individuals, not in R individuals. Conclusions: Our findings reveal an enterotype-specific response to an identical dietary modification, underscoring the value of integrating enterotype information into nutrition-intervention design and personalized nutrition strategies.