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Soy and experimental cancer: animal studies
E J Hawrylewicz1, J J Zapata, W H Blair
1Department of Research, Mercy Hospital and Medical Center, Chicago, IL 60616.
Abstract:
Studies are reviewed that report consumption of soy protein diets inhibits the growth of various tumors in rats. The inhibitory effect has been attributed to the phytoestrogens (genistein and diadzein) or protein kinase inhibitor in soy protein products. Recent studies indicate that additional factors in soy protein products may also contribute to the inhibition of tumorigenesis, namely the deficiency of the essential amino acid methionine. Metastatic growth to the lungs of a primary rhabdomyosarcoma tumor was inhibited by feeding a soy protein diet. The effect was reversed by methionine fortification of the diet. Carcinogen-induced mammary tumor development was inhibited during the promotional phase in rats fed soy protein isolate diet and reversed with a methionine-supplemented diet. Additional studies demonstrated that after excision of the primary mammary tumor, growth of additional tumors was inhibited when the diet was changed from casein to soy protein isolate. Histopathologic evaluation of the mammary tumors revealed more benign fibroadenomas and lower-grade adenocarcinomas in the soy protein group. Before carcinogen administration (at 7 weeks of age), ornithine decarboxylase activity and polyamine concentrations in the rat mammary epithelium were significantly lower in the soy protein group. These data suggest an inhibitory effect on mammary epithelial growth in the soy-protein-fed group.
Insights
Soy protein diets inhibit tumor growth in rats, potentially due to methionine deficiency. Supplementing methionine reversed this anti-tumor effect, suggesting methionine
Area of Science:
- Oncology
- Nutrition Science
- Molecular Biology
Background:
- Soy protein diets are known to inhibit tumor growth in animal models.
- Phytoestrogens and protein kinase inhibitors in soy have been implicated.
- Emerging evidence suggests methionine deficiency in soy protein may play a role.
Purpose of the Study:
- To investigate the role of methionine deficiency in soy protein's anti-tumorigenic effects.
- To examine the impact of soy protein on mammary tumor development and growth.
- To assess the influence of soy protein on mammary epithelial cell proliferation markers.
Main Methods:
- Review of studies involving soy protein diets in tumor-bearing rats.
- Dietary interventions with soy protein isolate and methionine supplementation.
- Analysis of tumor metastasis, development, and histopathology.
- Measurement of ornithine decarboxylase activity and polyamine concentrations.
Main Results:
- Soy protein diets inhibited metastatic rhabdomyosarcoma growth and mammary tumor development.
- Methionine supplementation reversed the inhibitory effects of soy protein.
- Soy protein diets led to more benign mammary tumors and reduced epithelial cell proliferation markers.
- Reduced ornithine decarboxylase activity and polyamine levels were observed in soy protein-fed rats.
Conclusions:
- Methionine deficiency in soy protein contributes to its tumor-inhibitory effects.
- Soy protein consumption can suppress mammary tumor growth and progression.
- Soy protein influences mammary epithelial cell growth potentially via modulation of polyamine metabolism.
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