Whey proteins protect more than red meat against azoxymethane induced ACF in Wistar rats.

Protein type and density have been shown to influence colon cancer risk using a carcinogen-induced rat model. It is suggested that red meat may promote colon cancer risk more than whey proteins. The aim of this study was to evaluate the influence of red meat, whey protein and their density in the diet on the number of aberrant crypt foci (ACF), preneoplastic markers in Wistar rats. The sources of protein, red meat as barbecued kangaroo muscle meat, and whey protein concentrate were fed to rats to provide 8, 16 and 32% protein by weight in a modified AIN-93 diet with low fiber, low calcium and high polyunsaturated fat. Adult Wistar rats (13 weeks of age) were fed these diets for 4 weeks and then two s.c. injections of azoxymethane, 15 mg/kg BW, were administered 1 week apart. Diets were fed for a further 8 weeks, rats were then killed, their colons fixed in formalin saline and stained with methylene blue to quantify ACF number. Fecal samples were collected and the fecal water was isolated for quantification of heme and thiobarbituric acid reactive substances. Increasing red meat density correlated positively, while increasing dairy protein density correlated negatively with rate of weight gain (p<0.05). Dietary intake was not significantly affected by protein type or density. The 32% whey protein group had significantly less ACF in the proximal colon in comparison to the 16 and 32% red meat groups (p<0.05). This reduction in ACF number in the whey protein group may be caused by hormones associated with the reduction in weight gain, and/or by components of whey protein concentrate such as cysteine, lactose and conjugated linoleic acid which have been shown to have anti-cancer effects. Using ACF number as an index, whey protein appeared to be more protective than red meat.

Dietary butyrate inhibits NMU-induced mammary cancer in rats.

Butyrate has been proposed as an antineoplastic agent, leading to the inhibition of tumorigenesis. The purpose of this study was to examine butyrate, supplied as tributyrin (Tbn) or as a natural component of anhydrous milk fat (AMF), on the development of nitrosomethylurea-induced mammary tumors in female Sprague-Dawley rats. Diets were 1) semipurified rodent diet (AIN-93) with high fat [20% sunflower seed oil (SSO), control], 2) SSO diet with Tbn added at 1%, 3) SSO diet with Tbn added at 3%, and 4) 19% AMF with 1% SSO diet, which contained butyrate equivalent to the 1% Tbn diet. These diets were fed ad libitum from weaning at 21 days of age, and at 24 days of age each rat was injected with nitrosomethylurea (50 mg/kg body wt i.p.). At any one period, there was a relative risk increase of 88% (p < 0.05) that rats in the SSO diet group would develop a mammary tumor compared with those in the AMF diet group. The addition of 1% and 3% Tbn to SSO diets reduced the tumor incidence by 20% and 52%, respectively, in comparison to SSO alone (p < 0.05). There was a linear inverse relationship between Tbn concentration and rats developing a tumor. From 89 days to the end of the experiment, rats fed the diet containing 3% Tbn showed a significantly lower multiplicity of palpable tumors (50% less at Day 118, p < 0.05) than SSO-fed rats. These results indicate that although the AMF diet was effective, particularly early in reducing mammary tumorigenesis, the 3% Tbn diet produced a sustained reduction of tumor multiplicity relative to the control (SSO) group. An inhibitory influence of butyrate on mammary tumorigenesis against a background of high polyunsaturated fat diet has been demonstrated in this animal model of breast cancer.