To examine absolute socio-economic differences in food habits and their changes over time.

A longitudinal study using the cohort baseline mail surveys conducted in 2000–2002 (n 8960, response rate 67 %) and the follow-up in 2007 (n 7332, response rate 83 %), including data on seven food habits recommended in the national dietary guidelines, as well as socio-economic and sociodemographic variables.

Data from the Helsinki Health Study survey, followed up for 5–7 years.

Municipal employees of the City of Helsinki, Finland.

Apart from fish and vegetable-based margarine on bread, the proportions of the recommended food items were higher for women than for men. The consumption of the recommended food items either increased or remained stable over the follow-up period. On the basis of the slope index of inequality (SII) it was observed that socio-economic differences widened with regard to the consumption of fresh vegetables and fish and use of vegetable-based margarine or oil in cooking, with the upper classes consuming these foods more often. The largest differences were observed in the consumption of fresh vegetables, for which the SII value among women was 2·38 (95 % CI 1·93, 2·95) at baseline and 2·47 (95 % CI 2·01, 3·03) at follow-up, and 3·36 (95 % CI 1·80, 6·28) and 3·47 (95 % CI 1·95, 6·19) for men, respectively. Socio-economic differences were non-existent for milk, and the reverse was observed for dark bread and vegetable-based margarine on bread.

Consumption of the recommended food items increased in the examined cohort over time. This increase was mostly similar throughout the socio-economic groups and thus the socio-economic differences remained stable. The upper classes followed the guidelines better with regard to the consumption of vegetables and fish and in the use of vegetable-based margarine or oil in cooking.