EFFECTS OF WHEAT BRAN AND ENERGY RESTRICTION ON ONSET OF PUBERTY, CELL-PROLIFERATION AND DEVELOPMENT OF MAMMARY TISSUE IN FEMALE RATS

Delayed onset of puberty and mammary development is assumed to reduce the risk of mammary cancer. An animal experiment was performed to investigate the influence of dietary fiber, which is known to affect hormonal balance, on these characteristics. Forty-five immature female rats were randomized into three groups, which were fed ad libitum a low-fiber diet (< 0.5% dietary fiber based on white wheat flour), a high-fiber diet (9.2% dietary fiber based on wheat bran), or an energy-restricted low-fiber diet providing 90% of the energy of the ad libitum low-fiber diet. Energy intake in the second and third groups was similar. Wheat bran slightly delayed onset of puberty, whereas restricted energy intake delayed onset of puberty by about six days. At 48-58 days of age, 14 rats of the low-fiber group, 10 of the high-fiber group and 7 of the restricted group were in cycle. Development of mammary tissue was rudimentary in rats of the energy-restricted low-fiber group, stronger in the high-fiber group and strongest in the ad libitum low-fiber group. Cell proliferation in mammary tissue was similar for both groups fed ad libitum, but significantly lower in the restricted group. Peroxidase activity, a biomarker for estrogenicity, was lower in the high-fiber group than in the two low-fiber groups. It is concluded that wheat bran and, even more effectively, an imposed restricted energy intake delays onset of puberty and mammary development. This shortens the time for mammary cells to be initiated to tumor cells and hence reduces the risk of mammary cancer development. It seems that wheat bran acts via a reduced energy intake. However, that wheat bran plays a role in the delay of mammary development due to a reduced exposure to estrogen cannot be excluded.