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Abstract & Commentary
Synopsis: Substituting nonhydrogenated polyunsaturated fatty acids for trans fatty acids may significantly reduce the incidence of type 2 diabetes in women.
Source: Salmeron J, et al. Am J Clin Nutr. 2001;73:1019-1026.
The long-term relationships between specific types of dietary fat and the risk of type 2 diabetes remain unclear. Because of this question, this study examined the relationship between dietary fat intakes and type 2 diabetes.
Salmeron and colleagues prospectively followed 844,204 women in the Nurses Health Study, aged 34-59 years with no diabetes, cardiovascular disease, or cancer beginning in 1980. Detailed dietary information was assessed at baseline and updated in 1984, 1986, and 1990 by using validated questionnaires. Relative risks of type 2 diabetes were obtained from pooled logistic models adjusted for nondietary covariates.
During the 14-year follow-up, 2507 incident cases of type 2 diabetes were documented. Total fat intake, compared with equivalent energy intake from carbohydrates, was not associated with the risk of diabetes. Intake of saturated or monounsaturated fatty acids was also not associated with the risk of diabetes. However, for a 5% increase in polyunsaturated fat the relative risk (RR) was 0.63 and for a 2% increase in energy from trans fatty acids the RR was 1.39 (P = 0.0006). Salmeron et al estimated that replacing 2% of the energy from trans fatty acids isoenergetically with polyunsaturated fat would lead to a lowered RR of 0.60.
Salmeron et al concluded that substituting nonhydrogenated polyunsaturated fatty acids for trans fats would likely reduce the risk of type 2 diabetes substantially.
Comment by Ralph R. Hall, MD, FACP
The evidence that a diet of fruits, vegetables, nuts and grains, and low in trans fatty acids and saturated fat will decrease mortality and morbidity continues to grow. We are beginning to see food producers change the preparation of the food that is delivered to the public so that the level of trans fats is reduced. The potential for reducing the incidence of cancer and cardiovascular disease with diet alone is immense.
There are some problems in this study, done by an accomplished group from the Harvard School of Public Health and the Division of Preventative Medicine and other accomplished scientists. The variability of the 3 fatty acid groups in the same foods is significant. Innis and colleagues have published a study demonstrating that this may result in large errors in the estimation of trans fatty acid intake of individuals and possibly groups.1 For instance, 5 breads made with partially hydrogenated fatty acids contained > 30% as trans fats. Whereas 5 breads prepared with nonhydrogenated fat contained < 2% as trans fatty acids. Fried chicken varied between 11.9% and 56.7%. The greatest variability was found in snack foods.
Despite these shortcomings, this study demonstrates the health potential of the reduction of trans fats in our diets.
This same group has published an important study that indicates that with the increase in obesity in the world the total fat intake has gone down. Thus, increased fat intake can’t take the blame for the obesity epidemic.2
Ralph Hall is Emeritus Professor of Medicine at the University of Missouri-Kansas City School of Medicine and Associate Editor of Internal Medicine Alert.
1. Innis SM, et al. J Am Coll Nutr. 1999;18:255-260.
2. Willett WC. Am J Clin Nutr. 1998;67(3 suppl):S5565-5567.