Final answer:
Calorie restriction (CR) is known to reduce the metabolic rate and production of free radicals, which may contribute to increased longevity and reduction in tumor growth, as observed in some animal studies.
Step-by-step explanation:
The established effect of Calorie Restriction (CR) is that it reduces metabolic rate and in turn the production of free radicals. When calories are restricted, the body adjusts its basal metabolic rate (BMR) to partially compensate for under-eating. This adaptive response leads to a lower metabolic rate to prevent the elimination of the body's own fat stores, which can also entail a reduction in the generation of free radicals, potentially linked to longevity benefits seen in some animal studies.
Throughout periods of prolonged fasting or significant calorie reduction, a decrease in BMR by up to 30% can be observed. This is due to the body's adaptive mechanism in times of scarcity, which helps to conserve energy. Furthermore, studies have linked the practice of calorie restriction with increased lifespan and reduction of tumor growth in laboratory animals, a phenomenon that may be attributed to decreased oxidative damage to DNA. However, it should be noted that the results from long-term primate studies have been inconclusive in demonstrating a lifespan increase.