NONPROMOTING EFFECTS OF LEAN BEEF IN THE RAT COLON CARCINOGENESIS MODEL

Recent epidemiologic studies have implicated red meat consumption as a risk factor for colon cancer in both men and women. However, it has b een very difficult to separate the effects of meat as a protein source from the accompanying fat content of the diets analyzed in these stud ies. Experimental data from rodent feeding trials show mixed results, with no firm conclusions being possible in terms of the colon-cancer p romoting effects of meat fat. The goal of the present study was to com pare, in an experimental animal model, the effects of beef with casein as a protein source, within the context of a low- and high-fat diet c ontaining either corn oil or beef tallow, on promotion of colon carcin ogenesis, Tumors were induced in Sprague-Dawley rats with 1,2-dimethyl hydrazine (20 mg/kg body wt for 10 weeks). Two hundred and eighty male weanling rats were randomized to eight dietary treatment groups of a 2X2X2 factorial design with fat source (corn oil vs, beef tallow), fat level (5% vs. 20%), and protein source (very lean beef vs, casein) as the factors. Diets were fed ad libitum before, during and after carci nogen treatment for a total of 27 weeks. At termination of the study, animals were examined for location, size and type of colon or extracol onic lesions. The total incidence and number of colon tumors were sign ificantly lower in the groups fed beef rather than casein. High fat le vels, regardless of source, significantly increased the number of colo n adenomas. These results demonstrate that when lean beef is used as t he protein source in the context of a low-fat diet, fewer intestinal t umors develop. These data do not support the belief that red meat cons umption increases the risk for colon carcinogenesis, but underscores t he importance of fat level in dietary context.