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Etiology

Dietary intake of monounsaturated and polyunsaturated fats reduced risk for coronary disease in women

ACP J Club. 1998 May-June;128:75. doi:10.7326/ACPJC-1998-128-3-075


Source Citation

Hu FB, Stampfer MJ, Manson JE, et al. Dietary fat intake and the risk of coronary heart disease in women. N Engl J Med. 1997 Nov 20;337:1491-9.


Abstract

Objective

To determine the association between dietary intake of total fat and specific types of fat and coronary heart disease (CHD) in women.

Design

Population-based cohort study of women in the Nurses' Health Study with 14-year follow-up.

Setting

United States.

Participants

80 082 female nurses who were 34 to 59 years of age in 1980. Exclusion criteria were cancer; angina, myocardial infarction, stroke, or other cardiovascular diseases; diabetes; and high serum cholesterol levels.

Assessment of risk factors

Nurses completed mailed questionnaires, including a food-frequency questionnaire, at baseline and every 2 years thereafter. For analysis, nurses were grouped into quintiles according to the percentage of energy obtained from different types of dietary fat (e.g., saturated, monounsaturated, polyunsaturated, trans unsaturated, and total fat). Multivariate analyses adjusted for age, time period, body mass index, smoking, menopausal status, parental history of premature myocardial infarction, multivitamin and vitamin E supplement use, alcohol consumption, history of hypertension, aspirin use, exercise, percentage of energy from protein, and total energy intake.

Main outcome measures

Fatal coronary disease (data from state vital records, the National Death Index, post office records, or next of kin) and nonfatal myocardial infarction (data from medical records assessed by physicians blinded to the women's reported risk status).

Main results

Total fat intake was not associated with risk for CHD (P = 0.55). Increased intakes of monounsaturated fat and polyunsaturated fat were associated with decreased risk for CHD (P = 0.05 and P = 0.003, respectively), and increased intake of trans unsaturated fat was associated with increased risk for CHD (P < 0.001). A positive trend was found for increased saturated fat intake (P = 0.10).

Replacing 5% of energy from saturated fat with energy from unsaturated fat reduced risk for CHD by an estimated 42% (95% CI 23% to 56%, P < 0.001). Replacing 2% of energy from trans unsaturated fat with energy from unhydrogenated unsaturated fat reduced risk by an estimated 53% (CI 34% to 67%, P < 0.001).

Conclusions

Women who had higher dietary intakes of monounsaturated and polyunsaturated fats had a decreased risk for CHD; those who had a higher intake of trans unsaturated fat and saturated fat had an increased risk. Total fat intake was not associated with risk for CHD.

Source of funding: National Institutes of Health.

For article reprint: Dr. F.B. Hu, Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA. FAX 617-432-2435.


Commentary

By documenting that different types of dietary fat are independent predictors of CHD, Hu and colleagues make an important contribution to the "diet-heart" hypothesis. This study confirms that increased consumption of saturated fat tends to increase risk for CHD, whereas consumption of polyunsaturated fat decreases this risk. The relation of monounsaturated fat intake to risk for CHD is less well established. Although believed to be "neutral" in their effect on cholesterol levels, monounsaturated fats can lower cholesterol levels when substituted for saturated fats and they may lower risk for CHD. Monounsaturated fats may also have other beneficial effects, such as inhibition of lipid peroxidation.

Observational studies have linked trans fatty acids to increased risk for CHD, an association presumably mediated by their effects on blood lipids and lipoproteins. These unsaturated fatty acid isomers are formed during the hydrogenation of vegetable oils, a commercial process intended to increase the hardness, stability, and shelf life of food products. To date, however, no large randomized trial has examined the health effects of replacing trans fatty acids with other fats or carbohydrates (1).

Controversy exists about dietary recommendations to limit total fat intake (2, 3); however, there is consensus that reducing saturated fat consumption helps prevent CHD. Replacing saturated fats with monounsaturated fats (from olive and canola oils) or polyunsaturated fats (from corn, soybean, and safflower oils) is reasonable. Decreasing trans fatty acid consumption by limiting intake of foods that contain partially hydrogenated oils should be an additional goal.

Joel A. Simon, MD, MPH
San Francisco Veterans Affairs Medical CenterUniversity of California, San FranciscoSan Francisco, California, USA


References

1. Position paper on trans fatty acids. ASCN/AIN Task Force on Trans Fatty Acids. American Society for Clinical Nutrition and American Institute of Nutrition. Am J Clin Nutr. 1996;63:663-70.

2. Connor WE, Connor SL. Should a low-fat, high-carbohydrate diet be recommended for everyone? The case for a low-fat, high-carbohydrate diet. N Engl J Med. 1997; 337:562-3.

3. Katan MB, Grundy SM, Willett WC. Should a low-fat, high-carbohydrate diet be recommended for everyone? Beyond low-fat diets. N Engl J Med. 1997;337: 563-6.