Our genetic makeup influences whether we are fat or thin by shaping which types of microbes thrive in our body, according to a new study. Scientists identified a specific, little known bacterial family that is highly heritable and more common in individuals with low body weight. So we are what we eat, and what we got from out parents. From the article: "The study, funded by National Institutes of Health (NIH), researchers sequenced the genes of microbes found in more than 1,000 fecal samples from 416 pairs of twins. The abundances of specific types of microbes were found to be more similar in identical twins, who share 100 per cent of their genes, than in non-identical twins, who share on average only half of the genes that vary between people. These findings demonstrate that genes influence the composition of gut microbes."