This review is a summary of three reference books and of the final report of a European concerted action. The data have been updated by an analysis of recent publications, according to the same methodological criteria as those used in the reference books: sample size, quality of questionnaire and statistical methods. Mechanistic hypothesis are considered for each microcompounds, the effect of which is situated along the natural history of cancer. Few studies have considered folates effect on breast cancer, and they observed an interaction with the risk related to alcohol consumption, which is decreased with a high intake of folates. Many studies considered the effect of vitamin C and E, and carotenoids, but results are inconsistent. Conflicting results were also observed in studies on fibre and breast cancer. However, although only half of the studies showed a protective effect, the strength of the biological mechanisms give support to the hypothesis of a protection provided by fibre. The situation is comparable with phyto-estrogens: epidemiological studies are scarce and few of them show significant protection, but several plausible biological mechanisms are proposed, either related to the negative modulation of estrogen receptor by phyto-estrogen, or to the inhibition of proliferation by action on various enzymes. At the present time, caution in the interpretation of the results and in the use of plant microcompounds in prevention or therapy is strongly recommended.