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PREVENTION OF ADULT TYPE OF DIABETES BY CHANGING DIETARY FAT

(May 2002)

Trans fatty acids are found when vegetable oils are partially hydrogenated to make stick and some tub margarines. They are also found in cookies (biscuits), shortenings, white bread and other baked goods, peanut butter, non_dairy creamers, and flour tortillas. Some trans fatty acids are found naturally in foods. According to investigators with the Nurses’ Health Study, 40 percent of adult onset (Type 2) diabetes can be prevented by substituting 2 percent of energy from trans fatty acid with polyunsaturated fats. This is based on a fourteen year follow up of 82,204 women, ages 34 to 59 years, 2,507 of whom developed diabetes. Repeated dietary histories were taken.

The argument is that, by increasing the amount of polyunsaturated fats (found especially in unhydrogenated liquid vegetable oils) and avoiding trans fatty acids, diabetes can be prevented. But, there was no progressive increase in diabetes risk as the amount of trans fatty acids in the diet increased, and only the highest trans fatty intake group showed a statistically significant 31 percent increase in diabetes risk. Furthermore, the increased risk ascribed to trans fatty acids was found primarily in women who were obese and non-exercising, and they are at high risk of developing diabetes anyway.

Commentary: This is an unpersuasive article. An accompanying skeptical editorial points out the problems in accurately determining trans fatty acid intake, made even more difficult by the changing trans fatty acid content of margarines as manufacturers have made softer margarines with ever smaller amounts of trans fatty acids.

As the authors of the editorial noted "one must consider the relatively small amount of trans fatty acid in the diet, the variability and specificity of food items containing trans fatty acids, the accuracy of food composition data used in the analysis and the likely associations of trans fatty acids with other nutrients".

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Weight loss and exercise help prevent adult onset diabetes. That has been clearly shown. Until we have better evidence, the glib notion that reducing trans fatty acids in the diet and replacing them with polyunsaturated fatty acids will cut the risk by 40 percent is not to be taken seriously.

Salmeron, J., et al. Dietary fat intake and risk of type 2 diabetes in women. American Journal of Clinical Nutrition. Vol 73 (June) Pgs 1019-1026. 2001. (Editorial page 1001).

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