Caloric Restriction and Resistance to Environmental DiseasesThe biological mechanisms for life-extension through caloric restriction make perfect evolutionary sense. In times of abundant food supply, rapid growth and fecundity are favored over endurance and longevity. Conversely, when food becomes scarce reproductive performance and growth are sacrificed in favor of extended total and reproductive life spans, thus increasing the probability that sufficient individuals will survive to restore the population when conditions improve. This scientific review of research literature relevant to caloric restriction effects and mechanisms shows that: Taken together, these effects suggest that caloric restriction in rodents produces a series of pleiotropic biochemical and physiologic effects consistent with a hypercorticism condition that is more severe in the early stages of caloric restriction than in the later stages and that occurs without concurrent hyperglycemia. The overall effect of this condition is to conserve energy by minimizing metabolism, proliferation, and nonessential functions in peripheral tissues. This in turn appears to minimize damage to the affected tissues so the progression of degenerative or neoplastic lesions is delayed. Surprisingly, they also report that the amount of food caloric-restricted rats consume in these studies, is typically equal or above the amount consumed by the non-restricted rats, when measured as calories per gram of body weight. In most strains of rodent used in caloric restriction experiments, body weight gain is reduced in the restricted animals to an extent where the body weight difference between the restricted and ad libitum-fed animals equals or exceeds the caloric deficit (Figure 1). Thus, during the latter half of a calorically restricted rat's life span, its caloric consumption per gram body weight is equal to or greater than that of its ad libitum-fed counterpart. For humans, caloric restriction holds the greatest promise for life-extension of the current anti-aging stragtegies. Antioxident supplementation may be helpful in moderation, but too much could be detrimental, as free radicals have a beneficial role to play in cell regulation and in fighting pathogens. DHEA supplementation may help elderly persons with a deficit of the hormone, but is harmful for younger persons who may become insensitive to the hormone later in life. And although glucocorticoids appear to play a significant role in producing the benefits of caloric restriction, their use in the absence of a caloric deficit may lead to hyperglycemia and diabetes. Finally, the authors of this extensive report note that caloric restriction can have a negative effect among patients with certain cancers, if begun after carcinogenic tumors have developed. Caloric restriction may help prevent cancers, but is not a cure for existing tumors, and may even make them worse. Another good reason to get a thorough doctor's exam prior to beginning any calorie reductive program, be it diet or a caloric restriction regime. |
|
