Dietary soy protein and isoflavones have no significant effect on bone and a potentially negative effect on the uterus of sexually mature intact Sprague-Dawley female rats.
OBJECTIVE
To evaluate the effect of dietary soy protein and isoflavones on bone and the reproductive tract in premenopausal rats.


METHODS
Three-month-old intact Sprague-Dawley female rats (N = 50) were fed diets containing casein, soy protein, or casein with isoflavone extract for 12 weeks. The amount of casein, soy protein, and extract (per kilogram diet) in each group was: (1) 200 g casein (control); (2) 100 g casein plus 100 g soy protein (low soy); (3) 200 g soy protein (high soy); 4) 200 g casein plus 17.2g extract (low extract); and (5) 200 g casein plus 34.4 g extract (high extract). Diet consumption, body weight, uterine wet weight, urinary deoxypyridinoline concentration, and bone mineral density of the femur and lumbar vertebrae were measured. Femur rigidity was evaluated by histomorphometry. The uterus and vagina were studied histologically.


RESULTS
Rats in all treatment groups had lower body weights and lower deoxypyridinoline concentrations compared with controls, but none of the differences was statistically significant. There was no significant difference in femur and lumbar bone mineral density, uterine wet weights, or histomorphometry between the control and treatment groups. Histologically, uteri and vaginae were normal in all groups except that 1 of 10 rats in the high-soy group and 2 of 10 rats in the high-extract group showed extensive squamous metaplasia in the uterine gland.


CONCLUSIONS
These results suggest that dietary isolated soy protein and isoflavones have no effect on bone and the vagina during premenopausal period, but may have an adverse effect on the uterus.
Nakai
Masaaki
M
Departments of Animal Sciences, University of Illinois, Urbana, IL, USA.
Cook
Leslie
L
Pyter
Leah M
LM
Black
Molly
M
Sibona
Jean
J
Turner
Russell T
RT
Jeffery
Elizabeth H
EH
Bahr
Janice M
JM
D000596:Amino Acids / Q000652:urine; D000818:Animals; D015415:Biomarkers / Q000652:urine; D001835:Body Weight; D015519:Bone Density / Q000187:drug effects*; D001842:Bone and Bones / Q000187:drug effects / Q000473:pathology; D004032:Diet; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage / Q000494:pharmacology*; D009929:Organ Size; D017697:Premenopause / Q000652:urine; D051381:Rats; D017207:Rats, Sprague-Dawley; D030262:Soybean Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D014599:Uterus / Q000187:drug effects* / Q000473:pathology; D014621:Vagina / Q000187:drug effects / Q000473:pathology
D000596:Amino Acids; D015415:Biomarkers; D007529:Isoflavones; D030262:Soybean Proteins; C036020:deoxypyridinoline