The article looks at conceptions of science and expertise among lay proponents of the low-carbohydrate high-fat diet in Finland. The research data consist of comments on a webpage related to a debate on the health dangers of animal fats screened in Finnish national television in autumn 2010. The article shows that contrary to the prevailing image advocated by the national nutritional establishment, which is based on the deficit model of public understanding of science, the low-carbohydrate high-fat proponents are neither ignorant about scientific facts nor anti-science. Rather, they express nuanced viewpoints about the nature of science, the place of individual experience in nutritional recommendations and the reliability of experts. Inspired by discussions on the social construction of ignorance, the article argues that the low-carbohydrate high-fat proponents are engaged in what it calls the social construction of competence when they present their position as grounded in science and stylize themselves as lay experts.