Effects of dietary n‐3‐to‐n‐6 polyunsaturated fatty acid ratio on mammary carcinogenesis in rats

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Abstract
We investigated the effects of the dietary n‐3‐to‐n‐6 polyunsaturated fatty acid (PUFA) ratio (n‐3/n‐6 ratio) on mammary carcinogenesis induced by 7,12‐dimethyl‐benz[a]anthracene in rats by feeding them several types of dietary fat with a fixed PUFA‐to‐saturated fatty acid ratio. Dietary fat was fed to the rats as 10% of the total feed weight, starting two weeks before the initiation. An increase in the n‐3/n‐6 ratio did not suppress the incidence or reduce the latency of mammary tumor development. The number and weight of mammary tumors per tumor‐bearing rat tended to be large in the group with an n—3/n‐6 ratio of 7.84 compared with those in the other groups. As the n—3/n‐6 ratios were elevated, the total number and weight of tumors increased gradually. The prostaglandin E2 (PGE2) concentration in mammary tumor tissue was markedly low in the group with an n‐3/n‐6 ratio of 1.03 compared with the group with an n‐3/n‐6 ratio of 0.01. In addition, PGE2 concentrations were almost constant when n‐3/n‐6 ratios were >1.03. These results suggested that the increase in the n—3/n‐6 ratio of dietary fat with the fixed PUFA‐to‐saturated fatty acid ratio cannot suppress the mammary carcinogenesis but can promote development of tumors, despite reduced PGE2 concentration in the tumor.

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