The gut microbiome has a significant influence on various diseases ranging from malnutrition to chronic inflammation. It is largely shaped by environmental factors, like diet and lifestyle. How the genetics of the individual affect the composition of the microbiome, however, was largely unknown. RUTH LEY explains in this video that the research team addressed this question by comparing the microbiome of over 1000 twin pairs based on DNA extracted from their stool samples. These comparisons allowed the researchers to compile a list of heritable microbes, top of which is a family of bacteria called the Christensenellaceae. One key finding was that the microbiome of lean individuals contains more of this type of bacteria as compared to the microbiome of obese people. Further experiments showed that, if Christensenellaceae are given to germ free mice, their amount of body fat is reduced. These results might lead to novel therapeutic approaches to obesity and associated diseases.