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New Study Questions Guidance About Fats and Heart Disease

Polyunsaturated fats increase risk of cardiovascular and coronary death (Feb. 5)

A study published in BMJ shows that replacing saturated animal fats with omega-6 polyunsaturated vegetable fats can increase the risk of death among patients with heart disease, calling into question dietary advice about fats and the risk of heart disease. The new findings could have important implications for worldwide dietary recommendations.

Advice to substitute vegetable oils rich in polyunsaturated fatty acids (PUFAs) for animal fats rich in saturated fats to help reduce the risk of heart disease has been a cornerstone of dietary guidelines for the past 50 years. The most common dietary PUFA in Western diets is omega-6-linoleic acid.

Researchers in the U.S. and Australia evaluated previously missing data from the Sydney Diet Heart Study — a single-blind, parallel-group, randomized controlled trial conducted from 1966 to 1973. A total of 458 men aged 30 to 59 years with a recent coronary event, such as a heart attack or an episode of angina, were included in the study.

The investigators used modern statistical methods to compare death rates from all causes (the primary outcome) and from cardiovascular and coronary heart disease in the recovered data.

The study participants were randomly divided into two groups. The intervention group (n = 221) was instructed to reduce saturated fats (from animal fats, common margarines, and shortenings) to less than 10% of energy intake and to increase linoleic acid (from safflower oil and safflower oil polyunsaturated margarine) to 15% of energy intake. Safflower oil is a concentrated source of omega-6 linoleic acid and provides no omega-3 PUFAs. The control group (n = 237) received no specific dietary instruction or study foods. Both groups underwent regular assessments and completed food diaries for an average of 39 months.

The results showed that the omega-6 linoleic acid group had a significantly higher rate of death from all causes compared with the control group (17.6% vs. 11.8%, respectively, P = 0.05). The rate of death from cardiovascular disease was also significantly higher in the intervention group versus controls (17.2% vs. 11.0%, respectively; P = 0.04), as was the rate of death from coronary heart disease (16.3% vs. 10.1%, respectively; P = 0.04).

The authors then used the recovered data to update an earlier meta-analysis. This also showed no evidence of benefit from replacing saturated fats with linoleic acid, and suggested a trend toward increased risks of death from cardiovascular disease and coronary heart disease.

The researchers concluded that their findings “could have important implications for worldwide dietary advice to substitute omega-6 linoleic acid, or polyunsaturated fatty acids in general, for saturated fats.”

Source: BMJ; February 5, 2013.

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