In this exploratory study, a sample of 20 four-year-olds took part in structured interviews in order to assess their biological knowledge of how the human body processes a food that they perceived to be fattening. There were two main outcomes to the study. First, the sample demonstrated knowledge of the digestive processes of ingestion, digestion/distribution and terminal digestive events that was broadly analogous to previous studies, and included a number of misconceptions. A minority of children could apply biological reasoning to make holistic sense of a series of linked, abstract physiological events. Data also revealed that young learners’ models of distribution of food away from the gut might be more sophisticated than previously reported, although none of the sample could provide any mechanism for distribution. Second, data were analysed quantitatively to give performance scores which were compared with children’s standardised body mass indices. Children of healthy weight displayed more accurate scientific knowledge of digestive processes than their overweight peers at statistically significant levels. Specifically, the healthy weight children had attained a more holistic understanding of these processes. This potentially has consequences for early years biology education since findings indicate, at a tentative level, that young, overweight children could be considered as having a distinctive special educational need. We propose that there may be a possible way forward for addressing the issues of overweight and obesity in young children by improving their understanding of digestive processes. These outcomes are aligned with calls in the literature for school science education to become more focused on aspects of scientific literacy such as health education. Further studies are recommended using larger samples from more diverse populations.