Chronic energy restriction versus energy cycling and mammary tumor promotion

Chronic energy restriction significantly inhibits mammary tumor promotion in rodents. The present work studied the effect of short-term, intermittent energy restriction or energy cycling on mammary tumor promotion since this feeding paradigm mimics the dieting habits of humans. Female Sprague-Dawley rats were given 7,12-dimethylbenz[a]anthracene (DMBA) at 50 days of age (5 mg ig). One week later, rats were randomly divided into three dietary groups. One group was fed ad libitum throughout the study (AL), another (ER) was fed 40% fewer calories than the AL group, and a third, energy-cycled group (EC) was fed in repeated cycles of 2 days of feeding at a level comparable to that of AL rats followed by 2 days of 40% energy restriction. At 10 weeks post-DMBA, the mammary tumor incidences in the AL and EC groups were the same, but incidence in the ER group was significantly lower. A second experiment examined serum levels of three hormones thought to play a role in mammary tumorigenesis. After 12 or 24 days on diet, ER rats had lower insulin levels compared with the other groups. Serum insulin levels in AL and EC rats were the same. After 24 days on diet, estradiol levels were significantly lower and corticosterone levels higher in the ER and EC groups compared with the AL group. Although energy cycling is a type of energy restriction that lowers overall weight gain and energy intake, it does not inhibit mammary tumor promotion as does chronic energy restriction. These data also suggest that feed efficiency and serum insulin levels correlate with susceptibility to mammary tumor promotion.