The link between the microbiota and obesity became even clearer when Gordon looked at a special strain of mice with no microbiota of their own. These intestinal tabula rasas proved to be strongly resistant to the fattening effects of unhealthy diets. After eight weeks on a 40% fat diet, these animals put on less than half as much weight as their normal peers, despite eating the same amount of food. When the team transplanted the microbiota from fat and lean mice into the germ-free strains, those colonised by microbiota from fat donors packed on far more weight than those paired with lean donors.