THE EFFECTS OF PATTERNED CALORIE-RESTRICTED DIETS ON MAMMARY-TUMOR INCIDENCE AND PLASMA ENDOTHELIN LEVELS IN DMBA-TREATED RATS

Chronic caloric restriction has been shown to inhibit mammary tumor pr omotion in the 7,12-dimethyl-benz[a]anthracene (DMBA) rat mammary tumo r model. The objectives of this study were to determine (i) the effect s of chronic caloric cycling (yo-yo dieting) on mammary tumor promotio n by high fat diets and (ii) the effect of three dietary regimens +/- superimposed mammary tumor burden on plasma endothelin-1,2 (ET) levels . Female Sprague-Dawley rats were treated with DMBA (5 mg/rat) and div ided into three dietary groups: ad libitum (AL) (containing 15% corn o il); 40% calorie restricted (CR) (containing 20% corn oil so consumpti on of fat was equivalent between AL and CR); a calorie cycled (CC) gro up fed alternatively AL and CR diets each 48 h period. After 10 weeks, tumor incidences were: AL, 63%; CR, 27%; CC, 57% (AL versus CR, P < 0 .05; CC versus CR, P < 0.05; AL versus CC, NSD). ET levels (pg/ml plas ma) were: AL, 16.0 +/- 6.54; CR, 32.31 +/- 0.34; CC, 23.44 +/- 5.04 (A L versus CR, P < 0.01; CC versus CR, P < 0.01; AL versus CC, P < 0.05) . Plasma ET levels were independent of tumor incidence and tumor burde n, but plasma ET levels were significantly increased in rats with a pr ior history of calorie restriction. As expected, maintained caloric re striction reduced mammary tumor incidence but intermittent caloric res triction (caloric cycling or yo-yo dieting) was without similar benefi t.