Accordingly to my late reading, "Our stolen future" by T.Colborn, levels of PCBs dioxins and other contaminants are very high in any animal foods. Because these contaminants accumulate in human fat tissue, and are ultimately excreted via breastmilk, thus becoming an horrible legacy, animal foods ( esp.fats such as butter, lard, whole dairy etc.) should be avoided as much as possible. Women from birth and until completed childbearing should be the more cautios in teh consumption of animal fats.
I am very interested in comments about the issue since I believe in the value of animal foods I say this after being raw-vegan for 2 years and witnessing my health decline under many aspects ( although I had some improvement in some limited areas).
I do believe the Weston Price / Nourishing Traditions approach is of some value, but these informations actually shook my confidence in a diet which suggests a high fat consumption from animal sources.