Implanted tumor growth is suppressed and survival is prolonged in sixty percent of food-restricted mice.

To examine the effect of food restriction on immune functions in the tumor-bearing state, mice were divided into a control group (fed 5.0 g diet/d; 71 kJ/d) and a 60% food-restricted group (fed 3.0 g diet/d; 43 kJ/d) at 8-wk of age, and 4 wk later, L1210 tumor cells were inoculated intradermally. In the food-restricted mice, tumor growth was significantly suppressed, and mean survival time after the tumor inoculation was prolonged (P < 0.05). The plasma concentrations of two antitumor cytokines, interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), were greater in the food-restricted group before tumor inoculation (P < 0. 05). Furthermore, the food-restricted mice had significantly higher plasma levels of IFN-gamma and TNF-alpha after tumor inoculation, although the treatment significantly increased these cytokine levels in both groups. Splenic natural killer cell cytotoxicity was also higher in the tumor-bearing food-restricted mice than in controls (P < 0.05). Food-restricted mice have strong antitumor immunity, and as a result, tumor growth is suppressed and survival time is prolonged in these mice.