Fat bodies are not, fait accompli, bad. Yet in our international research we found overwhelmingly that fat functioned as a marker to indicate health or lack of health. A body with fat was simply and conclusively unhealthy. This paper reports on how this unbalanced view of fat was tied to assessments of healthy bodies that were achieved by the act of looking. Despite the efforts of health education in each of the three countries in our study, children and young people cited the act of looking at bodies to assess health and when they did they arrived at the conclusion that fat on bodies is unmistakably bad. The paper uses a Foucauldian analysis of medical perception together with material from Conrad Gessner’s sixteenth century Historia Animalium to outline how the children in our study placed great reliance on information about fat to make almost exclusively visual assessments of health. The paper makes the case that, despite a great deal of health education in schools, these judgments reveal a tendency for children to make incorrect assessments of health.