For proper interpretation of results from epidemiological studies that use food-frequency questionnaires (FFQs), it is necessary to know the relationship between reported intakes from the FFQ and true usual intake. In this paper, we report a calibration study conducted to investigate the performance of the FFQ used in a cohort study, the Canadian Study of Diet, Lifestyle and Health.

Over a 1-year period, 151 men and 159 women completed a full set of questionnaires including a self-administered baseline FFQ, three 24-hour diet recalls administered by telephone, and a second FFQ self-administered subsequently. The association between the nutrient estimates derived from the FFQs and the diet recalls was evaluated by calculating deattenuated Pearson's correlation coefficients.

The FFQs estimated mean daily nutrient intakes higher than the diet recalls. When the log-transformed and energy-adjusted nutrient intakes from the average of three 24-hour recalls were compared against the baseline FFQ, the following deattenuated correlations were obtained in men and women, respectively: total energy 0.44 and 0.32, total fat 0.64 and 0.68, saturated fat 0.68 and 0.70, dietary fibre 0.65 and 0.44, vitamin E 0.32 and 0.37, vitamin C 0.40 and 0.37, β-carotene 0.34 and 0.29, alcohol 0.74 and 0.67, caffeine 0.81 and 0.76, with a median correlation of 0.49 and 0.53. Correlations between the second FFQ and diet recalls were similar. The correlations between the two FFQs as a test of reliability had a median value 0.64 for men and 0.63 for women for selected nutrients.

The study suggests that the FFQ method gives acceptable levels of nutrients or food component estimates, as assessed by this calibration study against diet recalls, when limited to energy-adjusted and deattenuated values.

This study sought to evaluate the benefit of utilizing a nutritionist review of a self-administered food frequency questionnaire (FFQ), to determine whether accuracy could be improved beyond that produced by the self-administered questionnaire alone.

Participants randomized into a dietary intervention trial completed both a FFQ and a 4-day food record (FR) at baseline before entry into the intervention. The FFQ was self-administered, photocopied and then reviewed by a nutritionist who used additional probes to help complete the questionnaire. Both the versions – before nutritionist review and after nutritionist review – were individually compared on specific nutrients to the FR by means, correlations and per cent agreement into quintiles.

Three hundred and twenty-four people, a subset of participants from the Polyp Prevention Trial – a randomized controlled trial examining the effect of a low-fat, high-fibre, high fruit and vegetable dietary pattern on the recurrence of adenomatous polyps – were recruited from clinical centres at the University of Utah, University of Buffalo, Memorial Sloan Kettering Cancer Center in New York and Kaiser Permanente Medical Program in Oakland.

Reviewing the FFQ increased correlations with the FR for every nutrient, and per cent agreement into quintiles for all nutrients except calcium. Energy was underestimated in both versions of the FFQ but to a lesser degree in the version with review.

One must further evaluate whether the increases seen with nutritionist review of the FFQ will enhance our ability to predict diet–disease relationships and whether it is cost-effective when participant burden and money spent utilizing trained personnel are considered.