Gut colonization with methanobrevibacter smithii is associated with childhood weight development

Objective To prospectively investigate the presence and counts of archaea in feces of 472 children in association with weight development from 6 to 10 years of age. Methods Within the KOALA Birth Cohort Study, a single fecal sample from each child was analyzed by quantitative polymerase chain reaction to quantify archaea ( Methanobrevibacter smithii, Methanosphera stadtmanae ). Anthropometric outcomes (overweight [body mass index {BMI} ≥ 85th percentile], age‐ and sex‐standardized BMI, weight, and height z ‐scores) were repeatedly measured at ages (mean ± SD) of 6.2 ± 0.5, 6.8 ± 0.5, 7.8 ± 0.5, and 8.8 ± 0.5 years. Generalized estimating equation was used for statistical analysis while controlling for confounders. Results Methanobrevibacter smithii colonization was associated with an increased risk of overweight (adjusted odds ratio [OR] = 2.69; 95% confidence interval [CI] 0.96‐7.54) from 6 to 10 years of age. Children with high levels (>7 log 10 copies/g feces) of this archaeon were at highest risk for overweight (OR = 3.27; 95% CI 1.09‐9.83). Moreover, M. smithii colonization was associated with higher weight z ‐scores (adj. β 0.18; 95% CI 0.00‐0.36), but not with height. For BMI z ‐scores, the interaction ( P  = 0.008) between M. smithii and age was statistically significant, implying children colonized with M. smithii had increasing BMI z ‐scores with age. Conclusions Presence and higher counts of M. smithii in the gut of children are associated with higher weight z ‐scores, higher BMI z ‐scores, and overweight.