Calorie Restriction

Calorie Restriction (CR) is the only well-researched, effective means of retarding fundamental aging that is available to post-embryonic animals. It has been shown effective in every living organism in which it has been tried, from single-cell yeasts to flies to roundworms to rodents to dogs and cats to -- it would appear from preliminary evidence -- non-human primates and even to humans.

CR, as applied to humans, means a reduction of one's calorie intake without any essential nutrient deficiencies, primarily for the purpose and hope of maximizing one's lifespan. For this end to be achieved, the reduction of calorie intake, which slows fundamental aging, must *not* be associated with any nutrient deficiencies, because such deficiencies tend to cause chronic diseases which themselves cut life short.

In other words, "calorie restriction" extends maximum lifespan by slowing the fundamental aging processes (whatever they may be), but in order to derive any benifit from that, a person must avoid diseaseas and other things which reduce average lifespan. Long term nutrient deficiencies are one thing that can lead to many of the chronic and (often) late-life diseases which kill most people. When restricting calories, it is therefore important to optimize the nutrient content of one's diet.

CR is therefore not the same as "going on a diet," or simply eating less, or starving oneself. It is a specific (though still diverse) set of dietary choices, based on the best available scientific evidence, with a specific goal in mind: life extension.

How Does One Practice CR?

Roy Walford's first book on CR, The 120-Year Diet, and the recent book, The Anti-Aging Plan, which he wrote with his daughter, Lisa Walford, both give extremely useful advice on how to practice CR. One or both of these books should be read by anyone planning to practice CR. Here I will bring up only a few relevant points for emphasis. First, it would be unwise to drop your caloric-intake extremely rapidly. Studies with rodents show that if energy-intake is dropped suddenly (switched from high to low from one day to the next, with no adjustment period), the rodents don't even live as long as the controls do. However, if the CR is instituted slowly, say, over the course of three months, the rodents have greatly extended life spans. In Walford's first book on CR, he suggested that one should take 4-7 years to go from one's normal level of intake to a severely reduced intake level, depending on various factors, age, what one is used to eating, etc. This was a conservative recommendation. Because such a small number of studies showing the optimal "caloric descent" time had been conducted, Walford probably just decided to take the descent time that he knew worked well in rodents, 3 months, and multiply it by the human:rodent life span ratio. But after his experience with the Biosphere 2 "experiment," in which energy-intake dropped fairly suddenly (though not in one day), he no longer believes that such a lengthy period of readjustment is necessary. Indeed, in the more recent book, one of the methods of instituting CR offered actually does involve a somewhat rapid drop in energy-intake. My own suggestion would be to drop your food-intake over the course of two years or so, just to be safe, unless you are at severe risk for one of the diseases that CR can (almost certainly) prevent, and prevent quickly, such as adult-onset diabetes, or heart disease. (Note that cholesterol levels in the Biospherians dropped far more than is achievable by any cholesterol-lowering drug.) If you are at risk for one of these diseases, then it might be better to go a little more quickly. I actually think just going by feel is probably not a bad idea. You should feel better on a CR diet (notwithstanding the hunger). If you feel light-headed or unusually tired, or have headaches, etc., you have probably dropped your energy-intake too quickly.

This talk of rates of "caloric-descent" and the like may make CR seem like an unmanageably complicated way of life, but the determination of the proper amount to eat is not complicated at all. One can simply go by weight. Both of the books on CR explain this in detail. The basic point is: figure out your "set-point," then weigh yourself every morning (or every few mornings) to make sure that, on avg., your weight is dropping a pound or two per month (or possibly faster, if that seems healthful), until you get to a point where you weigh about 15-20% less than your set-point, or perhaps 25% less than your set-point, if you want to do a more severe form of restriction. This is just a very rough guide. Many other factors would alter these numbers a bit, most importantly, your starting age (older people probably shouldn't restrict as severely), and your starting weight.

It is also possible to use skinfold calipers to measure changes in % body fat, and to set one's target level of energy-intake by setting a goal of a certain amount of body fat. One could measure one's starting % body fat, then shoot for a level of food-intake that results in a halving of that percentage. This is probably less precise than going by weight, but it might be a convenient method to use when travelling, for example. (Actually, when travelling for short periods, it is probably sufficient just to go by "feel" -- one gets used to how feelings of hunger correlate to food-intake.)

One could, however, ignore one's weight and body fat content altogether, and just count Calories. This is, after all, the method used in the most of the laboratory studies. This wouldn't need to be done every day, since most people eat approximately the same diet over the course of a few days, or a week. So one could just get a good idea of how many Calories one normally eats, then use a computer or nutrition tables to lower that a bit for the first month, then a bit more for the next month, and so on.

Indeed, with a nutritional analysis computer program, this is quite easy. Actually, even if you don't want to practice CR, I would suggest getting one these programs (some exist for free on the Internet -- more on that below, under "Nutrient Data in Electronic Form"), since most people have nutritional deficiencies, and using computers is the easiest way to discover what these deficiencies are.

[Bear in mind that the use of your current dietary habits -- measured as actual number of Calories consumed, or more loosely as your set-point or percentage body fat -- as the basis for the determination of optimal energy-intake is quite problematic. There are numerous non-biological determinants of dietary habits that operate in humans, but might not operate in laboratory animals. Still, setting a target intake-level based on your current habits, in conjunction with simply going by feel, as well as performing a few of the health-monitoring tests suggested by Walford (see the books), will most likely do the trick.]

In any case, one reason why a computer, or nutrition tables, would be necessary, even if you want to weigh yourself to determine your level of energy-intake (the "low" part of the high/low diet), is to insure you're getting enough essential nutrients (the "high" part). So if you just weighed yourself to insure that you're eating less, you probably would eventually be short on some essential nutrients. This might not matter too much for a very slight restriction, but for a severe restriction, the shortage in essential nutrients could be, ultimately, fatal. Malnourishment is not life-extending.

One way to avoid the use of computers and nutrition tables altogether would be to use the recipes and meal plans in the The 120-Year Diet, and, especially, The Anti-Aging Plan. The latter book, in fact, is mostly a book of "high/low recipes." I have tried several of these recipes. They are quite good, unless you need a few sticks of butter in each meal for it to taste good. The reason you can avoid the use of computers and nutrition tables here is that the Roy and Lisa Walford have done it for you. Just follow the recipes and meal plans, and you will be eating a high-nutrient, low-calorie diet.

I should say here, that, in my view, the concern shown by some practitioners of CR to avoid even the tiniest deficiency of a vitamin or mineral in their diet may be excessive. The idea seems to be that even a slight deficiency in one's diet can't be overcome with supplements, that there is something else in a naturally complete diet which no supplement has AND which would only end up being consumed in the right quantity if one's diet had at least the exact RDA's of known nutrients. To me, this seems unlikely, though Roy Walford might disagree. (Note that the "Biospherians" took vitamin B-12 supplements to overcome a B-12 deficiency in their diets, and suffered no noticeable ill-effects.) Consider the nature of the diets given to the rodents in most of the CR experiments. These rodents, in a way, "take supplements," since they're eating a fortified diet (as are the primates in the primate CR studies), so it's not at all clear that an unbalanced diet combined with supplements -- indeed, even a junkfood diet combined with supplements! -- wouldn't work. A somewhat conservative approach is, nevertheless, probably a good idea. I eat an extremely nutritious, variegated diet on the whole, but I'm occasionally slightly short on a couple of B vitamins. I let my multivitamin tablet make up the difference. There are so many errors in nutrition tables, and there are so many ways that recommended optimal levels of vitamin- and mineral-intake could be wrong or too unsophisticated (not taking nutrient interaction into account, for ex.), that worrying a lot about a slight shortage in a small number of nutrients, esp. when one can get those exact nutrients in a pill form, seems silly.

One final word: it is probably not a good idea to try to encourage kids to practice CR. If you are a parent considering putting a child on CR, I would definitely see a doctor. (You should probably see a doctor any time you want to make a radical in change in your, or your child's, diet, in any case.)

Resources

• CR Society

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