Zutphen was the only original cohort of the Seven Countries Study in which detailed information on the diet of all the participants was collected repeatedly, at intervals of 5 years. In the Zutphen Study, three dietary surveys were carried out between 1960 and 1970 and four between 1985 and 2000 in the Zutphen Elderly Study.
Collecting dietary data
The cross-check dietary history method was used to collect individual dietary data. The participant was interviewed at home by a dietician in the presence of the person who prepared the food, usually the wife. The dietician asked first about the general pattern of food consumption during a usual day. Then, based on the list of all foods consumed, what was eaten on a daily, weekly, or monthly basis. A cross-check was made with the food that was bought for the whole family during a week.
Processing the dietary data and calculating nutriënt intake
An average intake of individual foods was calculated from this information. These detailed data required a dietician’s interview of one to two hours and many hours to integrate the data into an average food consumption pattern, at the rate of one person a day. For calculating energy and nutriënt intake computerized food tables were used closest to the year in which the dietary survey was carried out.
Energy intake and dietary survey methods
Between 1960 and 1963 several comparative studies were carried out in subsamples of about 50 men. They showed that the the energy intake estimated with the cross-check dietary history method was about 200 kcal/day higher compared with the 7-day dietary record.
Reproducibility of the dietary history method
The reproducibility of the food intake was investigated in repeated surveys carried out three and 12 months after the initial survey. The foods groups bread, milk products, sugar products, and alcoholic beverages were well reproduced (correlation coefficients higher than 0.70). Correlation coefficients of 0.51 or less were found for meat and for vegetables.