Dietary soy isoflavone-aglycone lowers food intake in female rats with and without ovariectomy.
OBJECTIVE
Estrogens downregulate eating behavior, and soy isoflavones are known to be estrogenic agents. We aimed to examine whether the estrogenic property of soy isoflavones can affect food intake and body weight.


METHODS
Seven-week-old male, female, and ovariectomized (OVX) Sprague-Dawley rats were given free access to a diet containing 100-300 mg total isoflavone/kg diet, or to a control diet, either with or without concurrent administration of estradiol by subcutaneous implantation.


RESULTS
Dietary soy isoflavone was shown to lower food intake in female rats, whether or not the animals had undergone ovariectomy. Administration of estradiol lowered the food intake in male rats and in OVX female rats. The decrease in weekly food intake in female rats led to a reduction in their weekly gain in body weight. Dietary soy isoflavone significantly increased the concentration of serum isoflavones, especially equol (a metabolite of daidzein), regardless of gender or ovariectomy. Dietary soy isoflavone did not affect either serum estradiol concentration or uterine and didymus weights, but estradiol administration improved the uterine atrophy in OVX rats, and decreased the didymus weight in male rats.


CONCLUSIONS
Soy isoflavone lowers the food intake in female rats, but not in the male animals. Contrary to the hypothesis currently in vogue, the reduction in food intake caused by soy isoflavone may not be a purely estrogenic effect. This follows from the finding that the effects of soy isoflavones on food intake and on the reproductive organs differ from the corresponding effects produced by estrogen.
Kishida
Taro
T
Department of Biological Resources, Faculty of Agriculture, Ehime University, Matsuyama, Japan. kishida@agr.ehime-u.ac.jp
Mizushige
Takafumi
T
Ohtsu
Yohhei
Y
Ishikawa
Shimpei
S
Nagamoto
Manabu
M
Izumi
Tohru
T
Obata
Akio
A
Ebihara
Kiyoshi
K
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D019587:Dietary Supplements; D004435:Eating / Q000187:drug effects*; D004822:Epididymis / Q000187:drug effects / Q000473:pathology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007529:Isoflavones / Q000494:pharmacology*; D008297:Male; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D012727:Sex Characteristics; D014599:Uterus / Q000187:drug effects / Q000473:pathology; D047071:beta-Glucans / Q000494:pharmacology*
D007529:Isoflavones; D047071:beta-Glucans; C508230:soy isoflavone aglycone; D004958:Estradiol