Sept. 2010, Article 2
There is one tried and true method to live longer, but very few people want to follow it! It is called caloric restriction, or dietary restriction, and involves partaking of a diet that provides all required nutrients but reducing total food intake (measured in calories of energy) by 10 – 40%. This was first demonstrated with rodents by Clive McCay at Cornell in the 1930's, and has now been shown to apply not only to mice and rats, but also to fruit flies, nematodes, and in some sense even yeast. Caloric restriction studies in monkeys have not yet been completed, but medical results on these close cousins of the human species show clearly that their organ systems are aging less rapidly on a restricted diet than on their normal diet.
For the most part, the "gains from losing" are proportional to what you cut down. Reducing caloric intake by 10% extends lifespan in mice and rats by ±10%, while 20% reduction gives a ±20% life extension, and 30% is good for ±30% more life span. It looks as though 40% may be pushing the limits; in some mouse strains it extends life by 40%, but others just waste away and die (the fate of all strains at 50% reduction). Similarly, if restriction is started late, or stopped in mid-life, the benefits are roughly in proportion to the fraction of the life span for which it was practiced. It's almost as though each animal has a fixed life-time total caloric intake, and one can choose whether to use it up quickly or slowly.
No systematic experiments have been carried out on humans, and the ranks of those who voluntarily engage in caloric restriction are remarkably thin (as are the volunteers!). Even so, there are suggestive hints that this regime also works for people, provided they don't overdo it. (Those who went overboard on this, cutting caloric intake by 40% or more, had some serious health problems.) One encouraging bit of evidence is the observation that Seventh Day Adventists outlive "control populations" by nearly eight years. As part of their creed, Adventists consume a vegetarian diet, and refrain from drinking, smoking, dancing and cursing. They were compared to "controls" who neither smoke nor drink alcohol, leaving the lower-calorie-density vegetarian diet as a likely cause for their improved life span. However, it remains possible that the real key is not avoidance of meat, or reducing calories, but another aspect of their rather atypical lifestyle — perhaps even the forsaking of dancing or swearing! (Okay, neither is very likely; personally, I'd bet on the vegetarian diet.)
How does caloric restriction work? The first theory offered was that, in burning off excess calories, we generate harmful bi-products of metabolism, "free radicals" that can react with other molecules in our cells and damage them so they work less well. While this is almost certainly a part of the mechanism, there are other nuances to dietary restriction that don't quite fit that single-cause explanation. For one thing, animals that are fasted every other day ("alternate day fasting") get all the benefits of a restricted diet, even if they pig out on the fed days to make up for all the food they missed the day before. Another curious fact is that, at least in worms and flies, just the perception of food cancels most benefits of caloric restriction, even without ever eating it.
Essentially all animal species are genetically "wired" to assess the nutrients available, and to shift between low-food mode and reproductive mode as dictated by the environment. Thus, the evolutionary explanation for caloric restriction is that all animals have to be able to adapt to periods of both feast and famine. If resources are limited in your vicinity, it isn't a good idea to produce a lot of progeny, because then you may all starve. On the other hand, when food is plentiful, it is "good for the species" if everyone eats as much as possible, and uses the energy it provides to produce lots of offspring. Switching between those modes (long life coupled to delayed reproduction, vs. shorter life with early and high reproduction) is not a simple task, but eons of evolution have created the circuitry to flip from one mode to the other. That is essentially why some mammalian species hibernate, especially in colder climes, and why births are usually timed to the spring.
Robert J.S. Reis
Udupa Chair of Gerontologic Research
Professor, Depts. Of Geriatrics, Biochemistry & Molecular Biology, and Pharmacology/Toxicology
University of Arkansas for Medical Sciences
Copyright © 2010 RJR Reis. Used with permission.