<p><p>Data from market research firms are increasingly being used by social science researchers. These data provide potentially useful information, including detailed nutritional information and well-measured prices, and their panel structure is appealing as it permits researchers to control for unobservable time-invariant household characteristics and to model dynamic aspects of household behaviour. We summarise the information on the nutrients in foods that is contained in one source of market research data. We show that there is a lot of variation in nutrients at the individual product level, even within narrowly defined food categories such as butter. We also show that the duration of time over which data are collected can have important implications for analysis of household-level nutrient purchases.</p></p>