What constitutes healthy eating is experiencing ongoing public debate, and this debate is increasingly taking place on the Internet. In this article, using a dialectical approach to analyse rhetorical discourse, we investigated how six highly popular Finnish nutrition counselling bloggers construct dietetic credibility and understanding. Their argumentation is compared to that of two academic experts contributing to the blog of the National Institute for Health and Welfare. Theoretically, we draw on Michael Billig’s notions on how thinking and understanding are pervasively argumentative and reflect wider socio-cultural contexts, and on the dilemmatic nature of common sense. We demonstrate how the popular Finnish nutrition counselling bloggers rhetorically constructed a more particularistic and individualistic understanding of healthy eating in their argumentation in critical opposition to the universalistic and population-based understanding. In the popular Finnish nutrition counselling bloggers argumentation, practical, subjective and moral knowledge was valued, alongside abstract, scientific knowledge. In contrast, the National Institute for Health and Welfare bloggers typically utilised population-based averages and causalities in their argumentation. We argue that arguing over healthy eating in the public domain is fundamentally an epistemic struggle, in which different forms of knowledge and ways of knowing are valued, and dilemmas related to healthy eating are deliberated.