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Trans fatty acids and risk of coronary heart disease

Trans fatty acids are either manufactured or found naturally in products from ruminant animals. As it became known that saturated fats cause increased levels of blood cholesterol, the food industry was pressured to replace saturated fats in foods. However, polyunsaturated fats are unstable and go rancid at room temperature, so a process called hydrogenation is used to prevent this, which produces trans fatty acids. Current trans fatty acid intake contributes between 0.5% and 2.1% to total energy intake in western Europe. This study examines the relationship between trans fatty acid intake and the risk of coronary heart disease in a Dutch population.

Message

A 2% increase in trans fatty acid intake increases the risk of coronary heart disease by approximately 25%. It is therefore advisable to follow the current recommendation that trans fatty acids contribute no more than 2% of energy (about 5 g a day).

Reference

CM Oomen et al. Association between trans fatty acid intake and 10-year risk of coronary heart disease in the Zutphen Elderly Study: a prospective population-based study. Lancet 2001 357: 746-751.

Study

Participants were 667 men, aged 64 to 84 years, from the Zutphen Study (which was the Dutch contribution to the Seven Countries Study). The men were free of coronary heart disease when they were recruited. Dietary surveys, medical examinations and questionnaires were used to collect information on participants' diet and risk factors (including serum total and HDL cholesterol, blood pressure, physical activity and smoking) in 1985, 1990 and 1995. They were followed for ten years.

Participants were divided into tertiles according to the contribution of trans fatty acids to their total energy intake at the start of the study (less than 3.11%; 3.11% to 4.86% and more than 4.86%).

Incidence of coronary heart disease was obtained from national records, hospital discharge data or general practitioners. After ten years, a total of 98 coronary heart disease cases were recorded (49 fatal and 49 non-fatal).

Results

Average trans fatty acid intake decreased from 4.3% in 1985 to 1.9% in 1995.

A difference of 2% in energy from trans fatty acid intake (at baseline) was associated with a 28% increased risk of coronary heart disease (relative risk 1.28, 95% confidence interval 1.01 to 1.61). This result was adjusted for age, body mass index, smoking, use of vitamin supplements, intake of energy, alcohol, other fatty acids, dietary cholesterol and fibre.

The authors combined these results with those from three other follow-up studies, examining the association between trans fatty acid intake and risk of coronary heart disease (see Table 1). The pooled risk of coronary heart disease associated with an increase of 2% in energy from trans fatty acid intake was 25% (relative risk 1.25, 95% confidence interval 1.11 to 1.40).

Table 1. The effect of an increase of 2% energy from trans fatty acid intake on coronary heart disease reported in four follow-up studies.

Study Participants CHD cases Follow-up years RR (95% CIs)
Nurses' Health, 1997 80,082 women 939 14 1.62 (1.23-2.13)
Health Professionals, 1996 43,757 men 734 6 1.13 (0.81-1.58)
Alpha-Tocopherol Beta-Carotene Cancer Prevention, 1997 21,930 men 1,399 6 1.15 (0.96-1.35)
Zutphen Elderly 667 men 98 10 1.28 (1.01-1.61)

Comment

The current UK recommendation is that trans fatty acids should contribute no more than 2% of dietary energy (the equivalent of about 5 g/day). Trans fatty acids are found in natural foods such as milk, cheese, eggs and meat; in manufactured products such as oils, margarine and baked goods; and in deep-fried foods. Although this study found that the effect of trans fatty acids from manufactured and natural sources to be similar, the majority of trans fatty acids are consumed from either manufactured or deep fried foods. It would therefore be prudent to reduce consumption of these to decrease the risk of coronary heart disease. Trans fatty acids are not listed on food ingredient labels, but hydrogenated or partially-hydrogenated oils are, and so these are the ingredients to look for and either avoid or use sparingly.