The Nurses' Health Study also called the Harvard or Framingham Nurses' Health Study is an ongoing study of 80,000 or so women that started in 1984. All these women were tracked for daily diet as well as physical activity, weight, and disease. Deaths were recorded and cause of deaths. All this data has been studied, correlated, charted, and analyzed and several reports have been published in several scientific and medical journals. This is an attempt to show the findings.

The well-known Professor Willet, head of the Nutrition Department at Harvard has been in on these studies.

The following reports shows that even while keeping carbohydrate calories high, a change from eating better fats rather than reducing fats was more effective in reducing risk of heart disease. Other findings from this study show that high glycemic carbohydrates increase risk of heart disease and that trans fat increases risk of heart disease. It is also shown that a high-carbohydrate diet typically produces high plasma triglycerides and low HDL-cholesterol concentrations.


New England Journal of Medicine

Volume 337:1491-1499 November 20, 1997 Number 21

Dietary Fat Intake and the Risk of Coronary Heart Disease in Women

Frank B. Hu, M.D., Meir J. Stampfer, M.D., JoAnn E. Manson, M.D., Eric Rimm, Sc.D., Graham A. Colditz, M.D., Bernard A. Rosner, Ph.D., Charles H. Hennekens, M.D., and Walter C. Willett, M.D.

ABSTRACT

Background The relation between dietary intake of specific types of fat, particularly trans unsaturated fat, and the risk of coronary disease remains unclear. We therefore studied this relation in women enrolled in the Nurses' Health Study.

Methods We prospectively studied 80,082 women who were 34 to 59 years of age and had no known coronary disease, stroke, cancer, hypercholesterolemia, or diabetes in 1980. Information on diet was obtained at base line and updated during follow-up by means of validated questionnaires. During 14 years of follow-up, we documented 939 cases of nonfatal myocardial infarction or death from coronary heart disease. Multivariate analyses included age, smoking status, total energy intake, dietary cholesterol intake, percentages of energy obtained from protein and specific types of fat, and other risk factors.

Results Each increase of 5 percent of energy intake from saturated fat, as compared with equivalent energy intake from carbohydrates, was associated with a 17 percent increase in the risk of coronary disease (relative risk, 1.17; 95 percent confidence interval, 0.97 to 1.41; P = 0.10). As compared with equivalent energy from carbohydrates, the relative risk for a 2 percent increment in energy intake from trans unsaturated fat was 1.93 (95 percent confidence interval, 1.43 to 2.61; P<0.001); that for a 5 percent increment in energy from monounsaturated fat was 0.81 (95 percent confidence interval, 0.65 to 1.00; P = 0.05); and that for a 5 percent increment in energy from polyunsaturated fat was 0.62 (95 percent confidence interval, 0.46 to 0.85; P = 0.003). Total fat intake was not significantly related to the risk of coronary disease (for a 5 percent increase in energy from fat, the relative risk was 1.02; 95 percent confidence interval, 0.97 to 1.07; P = 0.55). We estimated that the replacement of 5 percent of energy from saturated fat with energy from unsaturated fats would reduce risk by 42 percent (95 percent confidence interval, 23 to 56; P<0.001) and that the replacement of 2 percent of energy from trans fat with energy from unhydrogenated, unsaturated fats would reduce risk by 53 percent (95 percent confidence interval, 34 to 67; P<0.001).

Conclusions Our findings suggest that replacing saturated and trans unsaturated fats with unhydrogenated monounsaturated and polyunsaturated fats is more effective in preventing coronary heart disease in women than reducing overall fat intake.

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American Journal of Clinical Nutrition, Vol. 73, No. 1, 132-133, January 2001
© 2001 American Society for Clinical Nutrition

Letters to the Editor

Reply to DL Katz
Simin Liu, JoAnn E Manson, Frank B Hu and Walter C Willett

Brigham and Women's Hospital, Harvard Medical School, Division of Preventive Medicine, 900 Commonwealth Avenue East, Boston, MA 02215, E-mail: simin.liu~channing.harvard.edu
Department of Nutrition, Harvard School of Public Health, Boston, MA 02215

Dear Sir:

We appreciate Katz's interest in our article. He suggested that because women who had coronary heart disease (CHD), angina, or overt CHD risk factors may have changed their diet to a high-carbohydrate one, the positive association between dietary glycemic load and CHD risk observed in our study may be spurious because of confounding by these high-risk conditions. This concern, although theoretically possible, was not supported by findings in the Nurses' Health Study. First, higher intake of dietary carbohydrate, total starch, or total grain was not significantly associated with higher CHD risk (1, 2); neither was intake of total fat (3). However, higher intake of trans fat (3) as well as lower intakes of polyunsaturated and monounsaturated fats (3), whole grains (1), and fruit and vegetables (4) were significantly associated with higher CHD risk. Second, nurses who had CHD, angina, or diabetes at baseline were excluded from the main analyses and higher dietary glycemic load was not associated with a less favorable CHD risk profile (Table 1 in reference 2). Third, the positive association between dietary glycemic load [i.e. carbohydrate glycemic load] and CHD [coronary heart disease] risk became even stronger after adjustment for conventional risk factors, arguing against the possibility of residual confounding.

Our findings that the types of carbohydrate as measured by the glycemic indexes are important for predicting CHD risk are consistent with an inverse relation between dietary fiber intake and CHD risk that we (5) and others (6) reported previously. Incorporating the concept of glycemic index in our assessment of the physiologic effect of carbohydrates enabled us to measure both the total amount of carbohydrate and the quality of carbohydrate intake. As shown in our article, the positive association between dietary glycemic load and CHD risk was independent of dietary fiber intake and was particularly strong in overweight women. This finding is supported by metabolic data showing that the adverse metabolic effects of high carbohydrate intake on blood HDL-cholesterol and triacylglycerol concentrations depend directly on the degree of insulin resistance, which is largely determined by excess body fat (7).

Although a prevalent nutritional recommendation has been that a low-fat, high-carbohydrate diet can prevent heart disease, few empirical data support such a recommendation (6). Results from the Nurses' Health Study add to the growing body of evidence suggesting that neither total fat nor total carbohydrate in the range typically eaten is related to CHD risk and that a more complex picture exists relating to different types of fats and carbohydrates. As in any field of scientific pursuit, new data often generate new hypotheses to be tested. Future investigations are thus needed to confirm our findings in high-quality prospective studies of different populations in whom the range and nature of carbohydrate intake and the degree of insulin resistance may be different. We do not advocate that dietary recommendations be based on epidemiologic data alone but do note that our findings are consistent with results from metabolic studies, including those cited by Katz. Additional basic and experimental studies are also warranted to achieve an understanding of how different types of carbohydrates may affect CHD risk. For example, why does a high-carbohydrate diet typically produce high plasma triacylglycerol and low HDL-cholesterol concentrations characteristic of the insulin resistance syndrome? How do different types of carbohydrates affect insulin and other hormonal responses, particularly in individuals who are already prone to insulin resistance? What other hemodynamic or inflammatory markers may also be related to such a diet?

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American Journal of Clinical Nutrition, Vol. 71, No. 6, 1455-1461, June 2000
© 2000 American Society for Clinical Nutrition

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Original Research Communications

A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women1,2,3

Simin Liu, Walter C Willett, Meir J Stampfer, Frank B Hu, Mary Franz, Laura Sampson, Charles H Hennekens and JoAnn E Manson

1 From the Departments of Epidemiology and Nutrition, the Harvard School of Public Health; the Channing Laboratory; and the Division of Preventive Medicine, the Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston.

2 Supported by CA40356, the main Nurses' Health Study Grant, and Nutrition Training Grant T32DK07703 from the US National Institutes of Health.


Background: Little is known about the effects of the amount and type of carbohydrates on risk of coronary heart disease (CHD).

Objective: The objective of this study was to prospectively evaluate the relations of the amount and type of carbohydrates with risk of CHD.

Design: A cohort of 75521 women aged 38–63 y with no previous diagnosis of diabetes mellitus, myocardial infarction, angina, stroke, or other cardiovascular diseases in 1984 was followed for 10 y. Each participant's dietary glycemic load was calculated as a function of glycemic index, carbohydrate content, and frequency of intake of individual foods reported on a validated food-frequency questionnaire at baseline. All dietary variables were updated in 1986 and 1990.

Results: During 10 y of follow-up (729472 person-years), 761 cases of CHD (208 fatal and 553 nonfatal) were documented. Dietary glycemic load was directly associated with risk of CHD after adjustment for age, smoking status, total energy intake, and other coronary disease risk factors. The relative risks from the lowest to highest quintiles of glycemic load were 1.00, 1.01, 1.25, 1.51, and 1.98 (95% CI: 1.41, 2.77 for the highest quintile; P for trend < 0.0001). Carbohydrate classified by glycemic index, as opposed to its traditional classification as either simple or complex, was a better predictor of CHD risk. The association between dietary glycemic load and CHD risk was most evident among women with body weights above average [ie, body mass index (in kg/m2) 23].

Conclusion: These epidemiologic data suggest that a high dietary glycemic load from refined carbohydrates increases the risk of CHD, independent of known coronary disease risk factors.

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More articles on results from the Nurses' Study will be posted later.