Polyunsaturated fats and cancer

The average intake of polyunsaturated fatty acids in the US has increased from about 3% of total energy intake in the 1950s to 6% today, and some authorities have recommended further increases in consumption, up to a maximum of 10% of total energy intake. The safety of increasing polyunsaturated fatty acid intake has been questioned, however, because theoretical concerns and animal experiments have suggested that diets high in polyunsaturated fat might increase the risk of cancer. In contrast, studies in humans have found little evidence of any association between intake of polyunsaturated fat and the risk of cancer.

In a new study conducted in Paris, France, researchers measured fatty acids in cholesterol esters in 3,277 middle-aged male subjects; 24-hour dietary recalls were also completed. During 9.3 years of follow-up, 59 men died of cancer. Men in the highest tertile of the distribution of linoleic acid (an n-6 polyunsaturated fatty acid) in cholesterol esters had a significantly lower risk of death from cancer compared with those in the lowest tertile. Subjects with cancer had a significantly lower intake of polyunsaturated fatty acids than those without cancer.

These data suggest that proportions of fatty acids in cholesterol esters are markers that predict premature death from cancer in middle-aged men. The authors stop short of concluding that there might be a, causal link between high polyunsaturated fat intake and some type of protection against cancer.

An accompanying editorial by Walter C Willett of the Harvard School of Public Health states that this study does little to resolve the question of a relationship between polyunsaturated fatty acid intake and cancer. The number of cancer cases was small and a variety of different types of cancer were included; moreover, most of the cancer deaths in the study population were probably attributable to smoking and excess alcohol intake, rather than to dietary factors. To detect realistic increases in the risk of cancer attributable to polyunsaturated fat intake, it would be necessary to include much larger numbers of cases with each individual type of cancer.

"Although there is currently little evidence that high consumption of polyunsaturated fat increases the risk of cancer in humans, those responsible for protecting the public's health should not forget the issue," Dr Willett urges. "The most reliable information will come from large prospective studies, including the multinational European investigation into cancer and nutrition, based on direct dietary assessment as well as on biochemical indicators of dietary intake."

Mahmoud Zureik, Pierre Ducimetiere, Jean-Michel Warnet, and Genevieve Orssaud, Fatty Acid Proportions in Cholesterol Esters and Risk of Premature Death from Cancer in Middle Aged French Men, BMJ 311(7015):1251-1254 (11 Nov 1995) [Correspondence: Dr Mahmoud Zureik, Institut National de la Sante et de la Recherche Medicale (INSERM), Unit 258, Hopital Broussais, 75014 Paris, France]

Walter C Willett, Polyunsaturated Fat and the Risk of Cancer [Editorial], BMJ 311(7015): 1239-1240 (11 Nov 1995) [Professor Walter C Willett, Department of Epidemiology and Nutrition, Harvard School of Public Health, 677 Huntington Avenue, Boston MA 02115]

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