Trans fatty acids in the Scottish diet. An assessment using a semi-quantitative food-frequency questionnaire

Trans fatty acids produced during hardening of oils have been associated with higher cholesterol levels and increased risk of heart disease. The potential risk from trans fatty acids may be greater in populations with relatively low intakes of essential fatty acids such as the Scots, who also have a high prevalence of heart disease. Means and ranges of trans fatty acid intakes are reported here for a Scottish population. A semi-quantitative food-frequency questionnaire was used to survey the diet of 10,359 Scottish men and women aged 40-59 years in 1984-6 as part of the baseline Scottish Heart Health Study. Trans fatty acid levels were calculated for each food item on the questionnaire and the total subdivided into that which is derived naturally (primarily by bacterial fermentation in ruminants) and that which is produced during industrial hydrogenation (hardening) of vegetable and fish oils. Means and ranges of intakes of each trans fatty acid variable were calculated by sex, age, smoking and social class groups. Mean total trans fatty acid intakes for men were 7.1 (SD 3.1) g/d, 2.7 (SD 2.9)% energy and for women were 6.4 (SD 2.9) g/d, 3.3 (SD 3.0)% energy. Industrially hydrogenated trans fatty acids made up nearly 58% of the total intake for men and 61% for women, with about 60% coming from cakes, biscuits and sweets, and 20% coming from the cheaper hard margarines. The main sources of the naturally derived trans fatty acids were red meat (27%), milk (20%), butter (18-19%) and cheese (13-16%). Differences between age, smoking and social class groups were apparent. However, apart from the social class differences of up to 1 g/d, these were so small that they are unlikely to be of any biological significance unless compounded by other factors such as marginal essential fatty acid adequacy. The possibility of trans fatty acid intakes up to 48 g/d and 12% total energy (compared with the Department of Health (1991) recommendations of 5 g/d or 2% energy) highlights the need for careful monitoring of the health risks at these high levels of intake.