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By Tim Lundeen  Beginning Noozer
Published: 21 October 2007 09:27 pm

- Calorie restriction refers to feeding an organism less than it would like to eat, typically from 20% to 50% less. In many organisms, such as nematode worms, mice, and rats, calorie restricted diets can significantly increase lifespans. A mouse that might normally live to the age of 3 might live to be 5 instead, a 65% increase in lifespan.

One theory for why this works is that organisms that are chronically hungry don't have enough resources to reproduce, and will put available energy into living longer, to try to stay alive through the bad times. Then when times are good, they put their energy into reproduction and ensuring the survival of their offspring. This theory has a fair amount of support from research, which suggests a common genetic basis and metabolic machinery for increased longevity with calorie restriction.

If calorie restriction worked for people in the same way that it works for mice, then someone on this regimen might live to be 140 or 150 years old. The problem is that we just don't know: what works for a simpler, shorter-lived animal may not be effective in a more complex, longer-lived human.  There have been drugs, such as Alteon's alagebrium, which were extremely effective in animals but had no discernable effect in humans. Some biogerontologists, such as Aubry de Gray, think that calorie restriction will not have any major effect on maximum human lifetimes. Others are more optimistic.

Despite the uncertainty, a number of people are experimenting with calorie restriction for their own diets. From their experience, CR (as it is known) has a number of very clear benefits (this list is reworked from The Longevity Diet):

• reduced average blood glucose levels, even in diabetics, so you have less damage from Advanced Glycation End products (AGE)
  
• increased maintenance of DNA and reduced expression of oncogenes, so you have less risk of cancer
• lowered blood pressure, so you have less risk of heart attack or stroke
• reduced risk of arthritis
• improved immune system
• improved mental functioning

CR has some distinct drawbacks as well:

• ongoing hunger urges. The benefits of CR may very well be tied to hunger and the hormone signals that hunger creates
• extreme thinness, to the point that other people may think you are sick or anorexic
• very low reserves of body fat. If you were in a situation where you had to live without food for a while (shipwrecked, say), you wouldn't last as long as someone with more body fat. Or if you came down with a serious illness such as pnuemonia, you would be more at risk than someone with more body fat.
  
• there is a lot we don't know. The blood markers we can measure all look good in people using CR. But the discovery that fasting results in much higher levels of methylglyoxal was made fairly recently. One of the ways in which people can reduce their calorie intake is through fasting, and there are still CR practitioners who recommend this. My own take is that fasting for more than one day at a time is not healthy; however, every other day should be fine.

Overall, my take on this is that CR is quite likely to increase your expected lifespan, and that the drawbacks appear to be relatively modest compared to the benefits. But then, I haven't tried it so can't say for sure; it certainly seems to be a highly personal choice.

What I am trying is skipping lunch, which is a very short-term fast, and I'm going to see how this affects me and the various blood-markers for health.