A study led by the University of Groningen reveals that the human gut microbiome is primarily shaped by environmental factors rather than host genetics. The research, published in *Nature*, analyzed the gut microbiomes of 1,046 healthy individuals from diverse ancestral backgrounds who shared a common environment. The findings indicate that the microbiome is not significantly associated with genetic ancestry or individual SNPs, and that host genetics play a minor role in determining microbiome composition. Instead, significant similarities in microbiome composition were observed among genetically unrelated individuals who shared a household, with over 20% of microbiome variability linked to factors such as diet, drugs, and anthropometric measurements. The study also demonstrated that microbiome data significantly improves the prediction of human traits like glucose and obesity measures compared to models using only host genetic and environmental data. The gut microbiome was found to be strongly correlated with many human phenotypes after accounting for host genetics, suggesting that microbiome alterations could be used to improve clinical outcomes across diverse genetic backgrounds. The research further showed that the gut microbiome is largely independent of host genetics, with heritability estimates as low as 1.9%. The study also found limited evidence of associations between individual SNPs and microbiome β-diversity, and that most previously reported associations were not replicated across different studies. The results were validated in a separate cohort of 836 Dutch individuals, reinforcing the conclusion that environmental factors play a dominant role in shaping the gut microbiome. The study highlights the importance of environmental factors in determining microbiome composition and underscores the potential of microbiome data in predicting human traits.A study led by the University of Groningen reveals that the human gut microbiome is primarily shaped by environmental factors rather than host genetics. The research, published in *Nature*, analyzed the gut microbiomes of 1,046 healthy individuals from diverse ancestral backgrounds who shared a common environment. The findings indicate that the microbiome is not significantly associated with genetic ancestry or individual SNPs, and that host genetics play a minor role in determining microbiome composition. Instead, significant similarities in microbiome composition were observed among genetically unrelated individuals who shared a household, with over 20% of microbiome variability linked to factors such as diet, drugs, and anthropometric measurements. The study also demonstrated that microbiome data significantly improves the prediction of human traits like glucose and obesity measures compared to models using only host genetic and environmental data. The gut microbiome was found to be strongly correlated with many human phenotypes after accounting for host genetics, suggesting that microbiome alterations could be used to improve clinical outcomes across diverse genetic backgrounds. The research further showed that the gut microbiome is largely independent of host genetics, with heritability estimates as low as 1.9%. The study also found limited evidence of associations between individual SNPs and microbiome β-diversity, and that most previously reported associations were not replicated across different studies. The results were validated in a separate cohort of 836 Dutch individuals, reinforcing the conclusion that environmental factors play a dominant role in shaping the gut microbiome. The study highlights the importance of environmental factors in determining microbiome composition and underscores the potential of microbiome data in predicting human traits.