Cancer is influenced by different factors: genetics, smoking, the environment, living conditions ¡K The role of nutrition in its development and/or its prevention is no doubt important but difficult to evaluate. Excessive consumption of fats (via the supply of energy) could increase the risk of cancer. Concerning the effects of the different fatty acids, research results are very contradictory. In summary, saturated fatty acids are considered rather neutral, monounsaturated would have a protective role, and polyunsaturates of the series n-6 (wƒn6) would seem to stimulate the growth of tumors (colon, prostate, pancreas¡K) whereas the ones in the series n-3 (wƒn3) would seem to inhibit and/or oppose the effect of the wƒn6 (this highlights the importance of the ratio wƒn6 /wƒn3). Moreover, studies on animals and on cellular streams show the beneficial effects of conjugated linoleic acid (CLA) (rumenic acid) in milk on colon cancer, breast cancer and skin cancer. However these effects have not yet been confirmed in humans.