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Long overdue changes coming soon:Changes since June, 1998:Changes since March, 1998:Changes since October, 1997:Note: none of the following should be construed as medical advice. Consult a doctor before undertaking any dietary changes.
Julius Pierce (julius@math.utah.edu) wrote the first CR FAQ for Sci.life-extension [1] in 1993, and I had been making emendations to it as new research became available, and as my own thinking about CR evolved. As time went on, this began to make the FAQ look a patchwork, so I decided to start from scratch and write a completely new FAQ.
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'Calorie restriction,' as it is used by life-extensionists, means a reduction in caloric-intake for the purposes of lowering one's rate of aging as well as preventing disease or the morbidity/mortality associated with disease. For these ends to be achieved, a restriction of energy-intake must not also be accompanied by restrictions of most other essential nutrients, especially vitamins and minerals, at least insofar as such restrictions in essential nutrients would result in sub-optimal intakes of these nutrients.
This is important: CR is not the same as "going on a diet," or simply eating less, or starving oneself.
One often sees other terms in the research literature, terms which connote a slightly different sort of diet, such as 'food restriction,' 'dietary restriction,' and so on. These different terms reflect, partly, different conceptions of the mechanism by which "CR" slows aging and prevents disease. In some cases, the terms also reflect different dietary regimens used in experiments. Part of this terminological and methodological confusion results from the difficulty in isolating the effects of a low-calorie diet from the effects of other aspects of the experimental diets. Some of the research that claims to be testing the effects of a calorically reduced, but not otherwise reduced diet has not, in fact, taken sufficient note of the reduction in protein that exists in the diets of the experimental animals, but considers protein only insofar as it contributes energy (calories) to the diet of the animals. Indeed, there are a few researchers who would call other researchers' "CR" experiments "PR" experiments.
The situation is even more complicated than this, given that minimal essential requirements for protein (for humans or rodents), as well as for other nutrients, have yet to be determined precisely.
Nevertheless, there is now widespread agreement that the reduction in energy-intake per se is responsible for most of the positive effects seen in these experiments, even if a few researchers think that the reduction in protein which usually exists in these experiments plays some role also.
The best terms to describe this sort of diet should perhaps be more general, like the 'anti-aging diet,' or 'high/low diet' (high in "good" nutrients, low in "bad" ones), or 'undernutrition without malnutrition' -- terms that Roy Walford often uses in his writings (see below for bibliographical info on some of his work). These terms capture the essence of the dietary anti-aging strategy, w/o presuming to have solved the technical questions about the absolutely optimal nature of an anti-aging diet, or the precise mechanisms by which the researched diets exert their effects.
Nonetheless, 'calorie restriction,' or just 'CR,' is in widespread use and captures the essence of the diet well enough that I will continue to use it, most of the time {![[CRS-6]](../../ics/crsl.gif){kind=small}
6} { 7}. I also sometimes call the practice of eating less for the purpose of living longer 'anorexia longaeva,' a term not without problems of its own.
There is something tremendously appealing about the idea that the world is divided into Good and Evil at all levels, from the social, down to the molecular. It is thus no surprise that the public has latched onto the idea that free radicals -- reactive "chemical fragments" -- are the primary cause of aging, and that any agent which is thought to render free radicals harmless -- such as vitamin C, beta carotene, or any other "anti-oxidant" -- will slow or even reverse aging when consumed in larger than normal quantities. As appealing as this idea is to most people, it is for the most part nonsense. That's not to say that free radicals play no role in aging, nor that anti-oxidants play no role in health maintenance.
Depending on the degree of dietary restriction used in an experiment, and the age at which the restriction is begun, CR animals can have a maximum life span that is up to 40% longer than the maximum life span of control animals (ad libitum fed animals). By 'maximum life span' I mean the age at which the longest living member of a group dies. (For technical reasons, it is sometimes better to consider the maximum life span of a group to be the avg. life span of the several longest-living members of a group. For purposes of comparison with controls, the result is essentially the same). Many studies that purport to be about aging just measure the average life span of all the animals in the study. A drug or dietary regimen that increase average life span but not maximum life span most likely does not slow the rate of aging -- it probably just prevents or reduces the incidence of certain diseases, or age of onset of these diseases. Such a drug or dietary regimen would thus not necessarily do anything positive at all for someone not prone to the disease or diseases in question.
By virtually all measures of youthfulness other than chronological age -- appearance, cognitive abilities, various biological parameters such as insulin-sensitivity, etc. -- CR animals are more "youthful" than their age-matched controls. The one possible exception is that fertility appears to be reduced in comparison to controls. For the most part, however, this is true only during the period of maximum fertility of controls, a period which is short relative to the full life span of the CR animals. But thereafter, one could almost say the reverse is true: that CR animals are more fertile than controls. Indeed, female CR animals can still conceive at an advanced enough age that all the control animals are dead, though with some species this may require temporarily giving them a little bit more food than they normally eat under CR.
CR can change the aging rate so dramatically that aging experiments which do not control for food-intake can, in some cases, be utterly worthless. For example, if an experimental group of animals is given megadoses of vitamin C by mixing it into their food, and they end up living longer than the controls, we cannot be certain that it was the C that altered their life span. Vitamin C might not taste very good to rodents, and the experimental rodents might not have eaten as much food because of the bad taste of the vitamin mixed in with it. It's also possible that vitamin C has a suppressive effect on the appetite. To take an example that Julius Pierce used in the original CR FAQ, researchers who have claimed that a lower fat intake among certain human populations has been shown to have a protective effect against cancer may be in error, since most low-fat diets will also be lower in calories (and this research doesn't or can't always control for caloric intake) { 1}.
CR probably slows aging by means of several of these mechanisms.
The evidence that bears on the question of the applicability of CR to humans then, is at present indirect. There is nonetheless a great deal of such indirect evidence, enough that we can say with an extremely high degree of confidence that CR will work in humans.
Until recent fairly hard data on primates and humans became available, most of the evidence that CR would work in humans was just this: CR experiments have been tried in many, many different species, and CR has been shown to work in all them, with a couple of odd and likely irrelevant exceptions (for example, the amoeba -- a species at an extreme evolutionary distance from homo sapiens -- becomes immortal if fed more than normal). Our beliefs about the efficacy or safety of other dietary regimens, and some drugs, come from studies performed on rodents alone, so there's no more reason to doubt the efficacy of CR for humans than there is to doubt the efficacy of these other diets or drugs. Bear in mind that CR has been successful in slowing aging in all higher organisms in which it's been attempted, which include many creatures other than rodents. I have not heard a good argument as to why the mechanisms whereby CR slows aging in all these creatures would have been "lost" by humans, or never would have evolved in our ancestral line.
In Roy Walford's first popular (geared towards laypeople) book devoted to CR, The 120-Year Diet, other arguments were made in favor of the applicability of CR to humans. (See Walford, 1986, for details.) Let me briefly mention the most interesting piece of data: Okinawans are the only large group of people who tend naturally to eat a diet approximating the high/low diet, though it is not as strict as it could be. They live much longer than genetically similar people on the other Japanese islands, who do not eat a high/low diet. It's not easy to see what other than CR could explain this difference in longevity.
The above conjectures were enough to convince me, and many others, that it would be foolish for someone who wants to live a long life not to practice CR (or not to try, at least, to practice CR). But recently, two things have greatly strengthened the case that CR will work in humans. One is the primate CR studies that have just begun to yield data, and the other is the "unintentional" experiment on humans that Roy Walford was able to perform.
Most of the researchers who remain skeptical that CR will slow aging in humans agree that if CR works in non-human primates, it will most likely work in humans. This is because monkeys are nearly identical to humans, genetically. Because the monkeys being studied have much longer life spans than rodents (true even of the relatively short- lived squirrel monkeys), it will be at least another decade before actual life spans between the experimental and control groups can begin to be compared, but the initial results suggest that the CR animals are aging at a slower rate. For example, one study has shown that puberty has been delayed in the monkeys in which CR was instituted at a young age. In addition, virtually all of the changes that are seen in CR rodents are being seen in the monkeys (again, it still a bit too early to know for sure in the case of some of these changes, but we'll probably know within a year or two -- though of course we'll still have to wait for the "hard" data of mortality).
As Roy Walford has put it, "for CR not to work in humans [or in other primates], all of our theories of aging would have to be wrong" (I'm paraphrasing). The idea here is, even though we don't have actual mortality data in the monkey studies or human studies, the changes seen in the monkeys -- changes in glucose metabolism, changes in anti-oxidant defenses, etc. -- are changes that, if our theories of aging are correct, would have to result in a slowed rate of aging. Again, this doesn't yield perfect certainty, since the theories could be wrong. But it seems unlikely that all, or even most of the theories, are totally wrong.
The objection might be raised that, although monkeys are nearly identical to humans genetically, they still don't live nearly as long as humans do, and thus the applicability of the monkey studies to humans may not be justified. As it happens, a situation arose accidentally in which a group of people were forced to do CR. This situation came about in the Biosphere 2 project. Again based on the results of this "experiment," we would have to conclude that CR will slow aging in humans, unless several of the leading theories of aging turn out to be completely wrong: the changes in fasting glucose levels and immunity seen in these people would most likely mean that they were aging more slowly. (See Walford, Harris and Gunion, 1992, and Walford and Walford, 1994, for details.)
Secondly, the point of CR isn't to be thin, it's to eat less, and to eat less in a specific way. Overweight people are under social pressure to be thin, so they may be more likely to eat less than skinny people, who often can eat as much as they want w/o gaining weight. So even if heavier people DID live longer than thin, healthy non-smokers, it wouldn't constitute evidence against CR's applicability to humans.
Finally, it's conceivable that some people who are thin are thin as a result of their eating less of a poor quality diet. This makes them "nutritionally analogous" to many people in the developing world, instead of being analogous to Okinawans, the only relatively large group in the world that "naturally" follows a high/low diet. Someone eating a diet of the same quality as the thin person eating the junkfood diet, but in greater quantities, might be able to overcome shortages in vitamins and minerals simply by virtue of the huge amount of food they're eating, even if it is junkfood. Thus, while the non-restricted junkfood-eating person (a person following a 'high/high' diet or 'sufficiently-high/high' diet) isn't getting any CR benefits, s/he is less likely to be short on vitamins and minerals, which might prevent certain types of early death suffered by someone eating the 'low/low' diet.
For me, and for most people who practice CR, or who are seriously contemplating practicing CR, the main questions are not whether CR will work in humans, but rather: 1) Is it possible that something better than CR -- something capable of slowing and reversing aging -- will come along soon enough that we don't have to do CR, but can just wait until the better method comes along? and 2) How can we deal with the hunger...? These questions are beyond the scope of this FAQ, though I will offer a few brief thoughts below. The Anti-Aging Plan: Strategies and Recipes for Extending Your Healthy Years of Life (Walford and Walford, 1994) has some excellent ideas on why a high/low diet might not leave one feeling as hungry as one might think.
The members of the CR Society who practice more than mild CR will themselves likely be part of a peer-reviewed article soon. Jordan Sparks, a member of the group, conducted a brief, informal survey of some of the members of the list. It gives some idea of the range of body-weight changes people on different degrees of CR experience.
The only currently available candidate that looks like it stands a chance of turning out to be as effective as CR is melatonin-replacement therapy. (DHEA does not look as promising, and other hormone-replacements need much more work.) Drop by a medical library from time to time to check on the status of the melatonin research. (And read Sci.life-extension -- with a skeptical eye, of course....)
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.)
4}: 1) hunger is limited to two or three days a week, which might be easier psychologically, and 2) the attendant weight-loss wouldn't be as great (the extreme, but periodic, restriction of the fasts seems to have a longevity-enhancing effect w/o a continual avg. reduction in caloric-intake).This would probably need to be instituted slowly, like the standard way of doing CR. You could just eat your first meal of the day -- on days when you want to fast -- later and later, until you're not eating at all on your fasting days.
This method of CR, however, has not been researched nearly as intensively as the other method. It is possible that there are unknown dangers to periodic fasting.
Another way to practice mild CR is simply to skip lunch. This is probably the easiest way to practice mild CR. An additional potential benefit of skipping lunch is the prevention of late afternoon fatigue. A recent study suggested that this benefit could be quite striking [5].
Slightly less extreme is the idea of ingesting substances which would absorb energy from food, or bind to food to prevent the body from utilizing the energy in it. I would also recommend not trying anything like this on a regular basis. However it may not be a bad idea to ingest some Questran or other fat-absorbing substances on occasions where one "pigs-out" on fat-laden food { 2}.
Finally, there is the option of pharmacological alteration of appetite. This too, would be risky, although some common, benign drugs exist which could make this a desirable option { 3}. Recent discoveries regarding leptin, GLP-1, and other elements in the body's hunger-regulating mechanism suggest that we may soon have safe, easy ways to alter appetite in a way which would make CR much easier.
5}
I don't eat lunch.
For dinner, when I'm eating at home, I usually have a large serving of a high-carotenoid veggie (kale, collards, etc.), sometimes stir-"fried" (no oil) with other veggies -- peppers, onions, etc. when I have time, or sometimes arugula (=arrugula, rocket, roquette, for the non-Americans); along with a good protein source -- beans of some kind usually; and a grain of some kind, usually rice. Sometimes I'll have a piece of fruit with dinner, or right before bed.
For a very interesting approach to meal planning on CR, see Tim Freeman's excellent page on his diet.
People interested in CR and exercise have typically answered the question with reference to Roy Walford's discussion in The 120 Year Diet (pp. 188-190). In his discussion, Walford draws on an older study by Goodrick, and on some of the early work of John Holloszy (who, since the publication of The 120 Year Diet, has gone on to do a number of other studies on CR and exercise).
The canonical answer, then, is that the increasing order of both maximum and average life span for rodents under different combinations of exercise and CR looks like this:
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1. non-CR'd, sedentary rodents. (Shortest-lived.) 2. non-CR'd, exercised. 3. CR'd and exercised. 4. CR'd and sedentary. (Longest-lived.) |
This makes sense from a theoretical standpoint that takes two things into account: 1) increasing one's "metabolic allotment," and/or decreasing metabolism (or making it more efficient) increases life span; and 2) exercise prevents some diseases of aging. We can leave out, for the moment, other things which play a role in the CR effect here, like improved handling of glucose, hormonal changes, etc.
So: Group (1) doesn't get the extra "metabolic allotment" of CR (somewhat controversial), or certainly, wastes energy in thermogenesis that the CR'd rodents don't waste, and doesn't get the reduction of the diseases of aging because of the lack of exercise. Group (2) gets the exercise benefits -- disease prevention -- but doesn't get the CR benefits. But their maximum life span is, in a few early studies, slightly increased, so there's possibly some anti-aging benefit per se to exercise alone. On the other hand (call me Tevye), male rats, when ad libitum fed, do not naturally increase their level of food-intake when they exercise, so it could be a kind of CR effect (if -- another qualification -- we can take CR to be a certain Calories needed:Calories consumed ratio, which is complicated -- see below). (See below [3e] for a reference to a study with female rats which exercised and did increase food-intake, and had an increase in average life span, but not maximum.) Group (4) lives the longest because CR appears to confer the disease-preventive effects of exercise (though possibly not all of them), while also resulting in a radical anti-aging effect. In Group 3, the exercise, one can reasonably guess, "uses up" one's metabolic allotment faster, and so partly negates the CR effect. There are other ways of understanding the group (3) effect, of course: more free radical damage results from exercise, etc. (note, though, that exercise increases defenses against free radical damage, according to many studies). Or perhaps the extra exercise makes the "effective CR level" too close to starvation (Calories needed:Calories consumed becomes too high).
Quite right. We need many, many more studies with many things varied and carefully quantified. (Although I do think we know enough to make good guesses about optimal exercise programs.)
What do we have now? A few new studies that help a bit:
Consider the Group (3) effect. The first qualification on the canonical answer to the CR+exercise question came in Holloszy's 1991 study [1e], in which the higher mortality of (3) compared with (4) was shown to be restricted to the first half of life. Of rodents that made it to past the 50% overall survival mark, exercise did NOT reduce the longevity-effect of CR. But what do we, who are starting CR in adulthood (not true in this study), make of this? Not much, I'd guess. Holloszy himself speculated that there might have been some unusual condition or disease that for some reason affected the CR'd rodents more than others, at an early age.
One possible problem: in all of Holloszy's recent studies the rodents doing CR plus exercise are CR'd to weigh the same the CR'd sedentary rodents, which means they ate a bit more.
Here are some details from the study:
There were four groups of rats (the strain was Long-Evans). The two of interest were the rats CR'd by 30%, and exercised, and those not exercised, but CR'd to weigh the same as the exercisers. It turns out that the degree of CR needed to match the weight of the exercisers is ~50%!
The amazing thing is that there was virtually no difference in mortality between the exercisers and the non-exercisers. If you look at the plot of mortality, you see that the average of the longest-lived 3 exercisers was around 1310 days, and the average of the longest-lived 3 non-exercisers was around 1360 days, but these animals are just "outliers" (statistically insignificant). The rest of the curve is essentially identical.
Note also that the amount run is around 4000-6000 meters/day at 17 months, going down with age gradually to 2000 or so. This is actually quite a bit of exercise.
So how do we apply this to the question of how much exercise we should engage in?
First, we should keep in mind that it is only one study.
But, if it's valid, a few things are worth noting. 30% restriction is a lot, for people. Most people who practice CR do not practice it that severely. With this assumption about how people practice CR in mind, and assuming the these results are robust, and _can_ be applied to humans, then exercising moderately while on CR is certainly safe, and it may even be safe to exercise more rigorously. The question is how to translate the 4000-6000 meters/day into human exercise. It obviously doesn't make sense to multiply it by the human:rodent body weight ratio, since running hundreds of miles/day would be impossible. But I don't know to what extent the human equivalent should be taken to be more than 4000-6000 meters.
I dug around a bit for data on career athletes and mortality a long time ago and found that they have a very "square" mortality curve. These were soft numbers so I wouldn't read much into it. (It wouldn't surprise me if there's some good data on this; I haven't looked too hard.) From what I saw, hard-working/playing aerobic athletes are much less likely to die young, but don't often make it past ninety.
I suspect strongly that when the dust clears, we'll see that the anti-longevity effect of exercise, when added to CR (in such a way as to keep body weight constant), kicks in only above a certain, very high, level of exercise.
But again, Paul's question: what is that level? What, exactly, is the human exercise equivalent of rodent wheel-running? Is it running a few miles a day, or is it more like climbing a few stair cases/day or brisk walking?
I agree with Doug Skrecky, generally, when he says that the risk of CR combined with exercise comes into play when either is at an extreme, except that adding a little CR to an intense exercise program seems to increase longevity (but not nearly to the level of longevity achieved by the addition of a little exercise to extreme CR).
But we need numbers. This is one of my priorities for my next CR research question, so I'll report back when I have some good data.
My advice: If the only relevant goal is longevity (or it radically eclipses other priorities), do extreme CR, with no aerobic exercise. That much strikes me as scientifically well-supported (certainly by comparison with the scientific support behind any other life-extension regimen).
Less extreme CR -- most of Holloszy's studies are with 30% restriction, probably more than most of us will achieve, by the way -- can probably be combined with exercise with less loss, probably no loss.
But advice on other combinations of degrees of CR and exercise are difficult even to speculate on. Take me, for example. I lift weights a bit, and don't exercise aerobically on a regular basis, but engage in extremely intensive physical activity periodically -- climbing mountains, hiking, etc. I have to increase temporarily my Caloric intake if I'm hiking all day. What does this cost me? Not much I'd guess, but I don't know. This sort of thing goes in the "Needed Real World Life-extension Experiments" file: get a bunch of rodents on CR, exercise them intensely on an erratic basis, giving them extra food during those exercise periods, and see what happens.
One more thing: if the treatment or prevention of depression is an additional significant goal (and you don't want to treat it with medication or psychotherapy), adding a tiny bit of aerobic exercise (brisk few mile walks 3-4 times/week) might reduce your longevity a tiny bit, if you're practicing an extreme CR, but probably not much more than a tiny bit.
| [1e] |
Holloszy JO; Schechtman KB. Interaction between exercise and food restriction: effects on longevity of male rats. J Appl Physiol, 1991 Apr, 70:4, 1529-35 . |
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| [2e] |
Holloszy JO. Mortality rate and longevity of food-restricted exercising male rats: a reevaluation. J Appl Physiol, 1997 Feb, 82:2, 399-403. |
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| [3e] |
Holloszy JO. Exercise increases average longevity of female rats despite increased food intake and no growth retardation. Journal of Gerontology, 1993 May, 48(3):B97-100. (UI: 93246574.) |
Disadvantages of Practicing CRAnother problem for some people is being skinny. Not everyone who did CR would end up skinny -- this depends in part on your starting point (your "set-point"). Yet all the people I've met personally who practice CR (about ten people) are skinny.
One possible disadvantage is that it may turn out to have been a waste of effort. This is the main reason, aside from not being able to deal with the hunger, that most people I know decide not to practice CR. They are convinced that they are going to make it to a time when better life extension methods exist, methods which will actually be able to stop the aging process, at which point one will be able simply to wait as long as necessary for the (virtually) inevitable: the time when the aging process can be reversed. One takes a risk with this approach, of course. In addition, CR lowers your chances of dying a premature death, as well as slowing the aging process. If CR prevents a case of terminal cancer that would have otherwise befallen you before the next Great Breakthrough in medicine, it will prove to have been worth it.
There are a few other disadvantages to practicing CR: one could not practice severe CR and engage in competitive sports requiring endurance; severe CR could make it difficult for some women to conceive (this is a complicated, and not-yet resolved issue), and doing CR while pregnant is most likely a stupid idea; and, finally, it requires an attention to food that some people may find annoying. Even practicing CR the way I, and some other people do -- not analyzing every meal for its nutritional content, etc. -- still requires some effort. At the level of restriction at which I'm currently eating, I find myself thinking about food much more often than I used to. I suspect, however, that I will probably adjust fairly soon.
John Woodman, a participant in the CR Society email list, conducted a brief, non-scientific survey of the side-effects of CR. Although, as John himself points out, the study is not rigorous, it is useful, and, based on my experience, fairly accurate. The survey asks about both advantageous and disadvantageous consequences of CR.
ANON1-1
.
Every practitioner of CR with whom I've spoken has claimed to feel a general increase in energy levels, something that may not be apparent from the rodent studies. One is certainly not "weighed-down" after meals (unless one practices CR by the fasting method). It's possible that energy levels of severely restricted people, as measured by physical activity actually performed in a given, short period, would actually be lower then that of "controls." Some of the rodent studies, and initial findings from the primate studies, bear this out. But the implications of these studies for people are difficult to assess. It could just be that random foot-tapping, drumming of fingers, and the like, would tend not occur as often under severe CR. Also, observed physical activity doesn't necessarily have anything to do with mental energy, or with the ability to engage in intense physical activity when such activity is needed. Moreover, in the long run, CR animals (rodents or humans) would end up having more energy than controls, simply because they live so much longer. (In fact, though it was thought for a while that the effect of CR resulted from the "candle not burning at both ends" -- i.e., that a purported lifetime allotment of metabolic energy was simply being used more slowly in CR animals -- it now appears that CR actually increases this allotment of energy, in addition to causing it to be used, on average, at a slower pace and in a more efficient way.)
Another advantage: you could save big on grocery bills.
A few people on the Net have written software to read the data. Ask in Sci.med.nutrition or Sci.life-extension. There is also a simple program at the University of Maryland Internet site for using the food composition data, but it may be insufficient for most people practicing CR. Recently, flaws in the USDA data have come to light, but the data set is probably fairly reliable, on the whole. There are a few commercial nutrition analysis programs available that have far more complete, reliable data. Most are quite expensive, though. Many of these programs were evaluated in the January, 1992 issue of the Journal of the American Dietetic Association. This journal also runs ads monthly on new programs. Some of the companies will send demo disks for free, so this would be one way of seeing whether the software meets your needs.
I have a copy of an article that was posted to Sci.life-extension recently containing a list of several shareware nutrition programs. I know nothing about these programs beyond what you will know after you've read the article.
One program designed specifically for people practicing Calorie restriction is called, not surprisingly, "Doctor Walford's Interactive Diet Planner". I played around with the program recently at a conference, and was favorably impressed. The company selling this program (with which I have no financial connection) is:
The Longbrook Company
1015 Gayley Ave. Suite 1215
L.A., CA 90024
(310) 392-8208 Fax (310) 396-9115
The company can be reached through email at the following address: 71510.2431@compuserve.com
Thanks,
Brian M. Delaney,
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( CALORIE RESTRICTION: FREQUENTLY UNANSWERED QUESTIONS ) |
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( THE INFINITE FACULTY: LIFE EXTENSION ) |