French consumers' perceptions of nutrition and health claims (NHC) are studied using both qualitative (n = 89) and quantitative (n = 1000) methods. We analyse the participants' unprompted associations between nutrients and foods and construct a "lay food composition table". We find evidence for a degree of familiarity, in most cases in name only, with macronutrients and a small number of micronutrients. We then turn to assessing how compatible nutritional claims are with the « lay food composition table » and with pre-existing, culture-based representations of the fate of foods in the body. We thus identify some principles predicting for positive or negative response in relation to types of claims. We also assess the credibility of types of claims according to the function cited and the carrier food. Finally, we test perception of hypothetical fortifications according to origin of nutrient and type of carrier food (e.g. omega 3 from fish oil in ham).we find (1) that the very principle of fortification disrupts culture-based representations French consumers have of the link between food and health, which they consider to essentially reside in a "varied and balanced diet". And that (2), in spite of a general disposition against NHC, some types of claims are deemed more acceptable and credible than others. The questions raised by these findings are whether and to what extent nutrition can, does and should replace food cultures.