Background – Both soy and whey proteins have been shown to have additional health benefits beyond their basic nutritional value, including anti-carcinogenic properties against colorectal, breast and prostate cancers. At present, limited knowledge exists of the mechanisms by which soy and whey exhibit these anti-carcinogenic properties and whether anti-tumour properties extend to other tissues.
Objective – To determine the effects of soy and whey protein-based diets on the incidence and progression of N- nitrosodiethylamine (NDEA)-induced, pre-neoplastic lesions and gene expression in the liver.
Design – Pre-neoplastic lesions were induced in the livers of Wistar rats by NDEA injections (25mg/kg body weight, 2 times week for 3 weeks). Rats (9 per treatment) were fed control (meat-based rodent chow), whey-based or soy-based diets for 15 weeks. Following euthanasia, liver samples were obtained and the total area occupied by preneoplastic lesions was determined by immunohistochemical staining for GST-yp. DNA microarray analysis is being undertaken to investigate the effects of the diets upon gene expression.
Outcomes – The incidence of preneoplastic lesions in whey-fed rats (0.31% total liver area) was reduced by 41% compared to rats fed a control diet (0.53% total liver area; P < 0.05). Soy-fed rats showed an 81% increase in lesion incidence (0.98% total liver area; P < 0.013).
Conclusions – Whey-based diets protect against initiation and progression of NDEA-induced preneoplastic lesions in liver compared to either meat- or soy-based diets. A similar pattern of protection has been observed against colorectal tumours. The molecular mechanisms of this protection remain to be elucidated.