Soy protein intake increased bone mineral density under nonenergy-deficiency conditions but decreased it under energy-deficiency conditions in young female rats

• Published in: Nutrition research (New York, N.Y.) N.Y.), 2022-10, Vol.106, p.1-11
• Main Authors: Kioka, Kazuki, Aikawa, Yuki, Wakasugi, Yusuke, Narukawa, Takahiro, Fukuyasu, Tomoya, Ohtsuki, Makoto, Yamashita, Takenori, Sasai, Nobuaki, Omi, Naomi
• Format: Article
• Language: English
• Subjects: Animals; Bone Density; Bone mineral density; Calorie restricted diet; Cancellous bones; Caseins - pharmacology; Estrogens; Female; Glycine max; Isoflavones - pharmacology; Osteoporosis; Rats; Rats, Sprague-Dawley; Soy bean proteins; Soybean Proteins - pharmacology
• ISSN: 0271-5317; 1879-0739
• DOI: 10.1016/j.nutres.2022.08.001

Many young individuals attempt to lose too much weight because of a false body image, which induces low bone mineral density (BMD) resulting from energy restriction. In addition, a decrease in estrogen has been observed along with the decrease in BMD. Estrogen is responsible for maintaining bone mass, and soybeans contain high levels of isoflavones, which have estrogen-like effects. Thus, we hypothesized that soy protein prevents low BMD caused by energy deficiency in young female rats. The purpose of this study was to examine the effect of soy protein intake on bone loss by energy deficiency in young female rats. Female Sprague-Dawley rats (6 weeks old) were randomly divided into the following 4 experimental groups: ad libitum feeding and casein diet (AL-Cas); ad libitum feeding and soy diet (AL-Soy); 40% energy restriction and casein diet (ER-Cas); and 40% energy restriction and soy diet (ER-Soy). The experimental period was 10.5 weeks. The AL-soy group had significantly higher BMD of the femur than the AL-Cas group (AL-Cas = 156 ± 5 mg/cm2, AL-Soy = 165 ± 7 mg/cm2; P < .05). Meanwhile, the ER-Soy group had significantly lower BMD of the tibia, femur, and lumbar spine than the ER-Cas group (ER-Cas = 147 ± 7 mg/cm2, ER-Soy = 133 ± 10 mg/cm2; P < .01). These results show that compared with ad libitum control groups, soy protein resulted in higher BMD under nonenergy deficiency, but under energy-deficiency conditions, it resulted in lower BMD. Female rats (6 weeks old) were divided into 4 experimental groups based on energy intake (ad libitum [AL] vs energy restriction [ER]) and protein type (casein [Cas] vs soy [Soy]). Soy protein intake under nonenergy deficiency resulted in higher bone mineral density (BMD) (AL-Soy group). However, energy deficiency inhibited BMD gain during the growth period (ER-Cas and ER-Soy groups). Furthermore, soy protein intake under energy deficiency exacerbated the low BMD (ER-Soy group). [Display omitted]