Our microbiome, the collective genomes of the microbes that live inside our digestive systems, has been linked to multiple facets of our health, from cancer to depression and everything in between. However, before you go recommending one probiotic over another, you might want to read ahead.

Large studies have revealed significant variation between the gut microbiome of both healthy individuals and those with health conditions, making it hard to identify associations between the gut microbiome and a person’s health. However, thanks to two recent studies (one in Amsterdam and one in Guangdong, China), the reasons for this variation are now clearer. The two studies showed that both ethnicity and geography are key factors in determining the gut microbiome. It gets even more complicated: most of the current knowledge about the connections between the microbiome and health come from studies of European and North American populations.

This new research highlights the importance of being careful when applying data about the gut microbiome to different groups of people: clearly, one size does not fit all. However, researchers still don’t know why differences in the gut microbiome are associated with ethnicity and geography. We’ll need to untangle the influence of genetics, cultural norms, and diet if we want to develop personalized microbiome-based treatments.