INVITRO BINDING OF ESTROGENS BY DIETARY FIBER AND THE INVIVO APPARENT DIGESTIBILITY TESTED IN PIGS

Within the framework of experiments related to the association between dietary fiber and breast cancer an in vitro test system was used to study the binding of estrogens to various fibers (e.g. cholestyramine, lignin and cellulose) and fiber sources (e.g. wheat bran, cereals, seeds and legumes). Furthermore, the in vivo apparent digestibility of the different fiber sources was tested using a mobile nylon bag technique in intestine-cannulated pigs. Estradiol-17-beta (E2) bound more strongly to the various fibers than did estrone (E1), estriol or estrone-3-glucuronide. At increasing pH (> 7) binding of both E1 and E2 to wheat bran decreased significantly. Cholestyramine and lignin bound almost all estrogens present in the medium. Linseed (91%), oats (83%), barley chaff (88%) and wheat bran (82%) are other excellent binders of E2. Com, rye and white wheat flour showed lower binding capacity with a relatively low affinity. Cereals with the highest percentage of lignin in the fiber (> 3%) were also the fiber sources with the lowest apparent digestibility. Estrogens bound with the highest affinity (relative to bovine serum albumin) to these fiber sources. Together with wheat bran and lignin, oats, linseed and soybean seem to be products with good perspectives for in vivo evaluation of the lowering effect of dietary fiber on estrogen exposure of estrogen-sensitive tissues.