Diet history: questionnaire and interview techniques used in some retrospective studies of cancer.

A detailed diet history method that has been used by the Epidemiology Unit of the National Cancer Institute of Canada, Toronto, in retrospective case-control studies is discussed. The questionnaire format and the method of administration by trained interviewers, together with instructions used to train the interviewers, are described. The questionnaire items elicited the usual frequency of foods consumed in the Canadian diet for one or two specified periods of time, including current and/or past diet history. Various probes required to elicit proper information on frequency, serving size, and additions to food are discussed. Portions were quantified by using geometric food models made of papier-mâché, wood, and plastic. The frequency and volumetric measurements obtained from the diet history questionnaire were converted to gram weights using the density of each food consumed; the nutrient intakes were then computed.