To evaluate the reproducibility of, and to compare and calibrate, diet measures by the Northern Sweden 84-item food-frequency questionnaire (FFQ) with measures from 24-hour diet recalls (24-HDR).

Randomly selected respondents (n=246) from the EPIC (diet-cancer) and MONICA (diet-cardiovascular disease) study cohort in Northern Sweden were invited to answer the FFQ twice over a one-year interval (FFQ1 and FFQ2), and to complete ten 24-hour recalls (reference method) in the months between. Plasma β-carotene concentrations were determined from a subset of 47 participants.

Vasterbotten and Norrbotten, Northern Sweden.

Ninety-six men and 99 women, who completed the study.

The reproducibility of the FFQ was high in terms of both mean energy and nutrient intakes and relative ranking of participants by intake levels (median Pearson correlation of 0.68). Moderately higher food intake frequencies were recorded by FFQ1 compared with 24-hour recalls for dairy products, bread/cereals, vegetables, fruits and potato/rice/pasta, whereas meat, fish, sweet snacks and alcoholic beverage intakes were lower. The median Spearman coefficient of correlation between FFQ1 and the average of ten 24-HDR measurements was 0.50. Daily energy and nutrient intakes were similar for FFQ1 and 24-HDR measurements, except for fibre, vitamin C, β-carotene and retinol (FFQ1<24-HDR) and sucrose and cholesterol (FFQ1>4-HDR). Pearson coefficients of correlation between FFQ1 and 24-HDR corrected for attenuation due to residual day-to-day variation in the 24-HDR measurements ranged from 0.36 to 0.79 (median 0.54). Adjustment for energy had only very moderate effects on the correlation estimates. Calibration coefficients estimated by linear regression of the 24-HDR on the FFQ1 measurements varied between 0.30 and 0.59 for all nutrients except alcohol, which had calibration coefficients close to 1.0. These low calibration coefficients indicate that relative risk estimates corresponding to an absolute difference in dietary intake levels measured by the FFQ will generally be biased towards 1.0. Plasma β-carotene levels had a Pearson coefficient of correlation of 0.47 with the 24-HDR measurements, and of 0.23 with FFQ1 measurements.

The Northern Sweden FFQ measurements have good reproducibility and an estimated level of validity similar to that of FFQ measurements in other prospective cohort studies. The results from this study will form the basis for the correction of attenuation and regression dilution biases in relative risk estimates, in future studies relating FFQ measurements to disease outcomes.

To determine changes in reported food frequency in adults between 1986 and 1999.

Four consecutive cross-sectional surveys.

Counties of Norrbotten and Västerbotten, Northern Sweden.

The Northern Sweden MONICA (Monitoring of Trends and Determinants in Cardiovascular Disease) population, four independent cross-sectional surveys in 1986, 1990, 1994 and 1999. Randomly selected age-stratified samples of the population aged 25–64 years. Analysis is based on 2982 males and 3087 females who completed an 84-item food-frequency questionnaire.

Between 1986 and 1999, average reported consumption of 3%-fat milk decreased from 42 to 7 intakes month-1 in men and from 28 to 4 intakes month-1 in women. Reported use of 1.5%-fat milk increased from 6 to 27 intakes month-1 in men and from 6 to 24 in women. Monthly intakes of potatoes and root vegetables decreased from 38 to 27 in men and from 39 to 32 in women. Consumption of pasta increased from 4 to 7 intakes month-1 in both sexes. Intakes of solid fats with 80% fat content dropped from 92 to 62 per month in men and from 78 to 52 per month in women, whereas use of 40%-fat spread increased from 12 to 22 intakes month-1 in men and from 5 to 26 in women. Monthly intakes of vegetable oil increased from 3 to 12 in men and from 3 to 15 in women. The percentage of overweight or obese individuals (body mass index >25 kg m-2) increased from 52 to 65% in men and from 41 to 52% in women (P for linear trend in all these changes, <0.001).

Our data indicate reduced consumption of foods with a high content of saturated fats. In spite of that, there is an unbroken trend towards increased obesity.