As a first principle, there is, or rather should be, no such thing as a "diet" in the sense of a temporary alteration in eating habits, in order to get back to some prior desirable weight or size. Any temporary eating change will lead only to temporary changes in weight. A diet in the best sense of that term is essentially a life-style choice to be followed indefinitely. This is not to say that one’s diet should not change or possess great variety or be delicious. Indeed, as scientific knowledge about the diet-health-longevity nexus advances, one would expect to alter one’s diet. Healthy diets would be generally expected to incorporate a wide variety of foods and they should be mostly great tasting.
A second principle is that there is certainly no single best diet for everyone. There is enormous genetic variation among human beings (e.g. height, bone density, skinfold thickness, body fat, fat-free mass, and body fat distribution have all been shown to have a genetic influence). That variation will likely reflect itself in widely varying micro- and macro-nutrient requirements and ideals. Many diseases are known to have at least some genetic causation (e.g. Type 1 diabetes which is more common among Caucasians than African-Americans or Native-Americans, familial hypercholesterolemia, hereditary hemochromatosis, among many others). While great progress has been made in specific cases, very little is generally known about the implications of the genetic diversity of human beings for optimal diets. Moreover, there is considerable variation in dietary needs at different exercise levels and at different stages of the life cycle. For example, a fit, trained athlete will require more calories, water, iron, and certain B vitamins. Nutritional requirements and ideals will vary during pregnancy, infancy, adolescence, and in old age. Hence, what follows is of necessity general (and written largely from the perspective of an active adult)—if in doubt, seek medical advice.
A third principle, underlying the present effort, is that the proper diet for a given individual should be based on the best information that science has to offer. Some people may, for personal religious or ethical reasons, not wish to include items in their diet that would otherwise be healthy for them. Others may avoid or embrace various dietary measures out of ignorance (see "Fads, Frauds, and Quackery," by S. Barrett and V. Herbert, Chapter 109 in Modern Nutrition in Health and Disease, 9th Edition, M. Shils, J. Olson, M. Shike, and A. Ross, eds. 1999). This is the "bible" of the traditional nutritional establishment, incidentally, and may be referred to sporadically. In general, I will minimize references and attempt to keep everything as simple and readable as possible. The goal, then, is to understand the science relating diet to health and longevity. If the science of a topic is "controversial," I’ll note that as I go, along with providing some sections of specific controversies at the end.
The Key Insight: Calorie Restriction Reduces Disease and Extends Life
In literally thousands of experiments, on a wide range of animals (almost certainly to include humans!), calorie restriction has greatly extended maximum and average lifespans and improved disease resistance, including resistance to many cancers. There is still uncertainty about why calorie restriction has these desired effects. Two important reasons proposed for the benefits of calorie restriction are: 1) fewer calories mean that there will be a reduction in the accumulation of oxidant and free-radical damage, and 2) fewer calories alter fat deposition, obesity, and hormones. The practical effect of this is improve the immune response of calorie-restricted (hereafter CR) animals. There are numerous reputable websites to learn more about the underlying animal studies (preliminary corroborative results are now coming out on the rhesus monkey experiments currently underway). Indeed, there are already convincing studies demonstrating the health benefits (and, no doubt, the longevity benefits…though not enough time has passed to observe these!) in humans. See the Sears and Walford references in the bibliography, and for a fascinating more general account of why we age check out Austad. For present purposes, that CR—with adequate or optimal nutrition (the first controversy)--is good for your prospects for a long, healthy life will be taken as a given. The science is unambiguous and the life extension benefits have been known (surprisingly) since 1935. The interesting questions revolve around related issues.
What is Calorie Restriction?
You might (in an ideal world) want to get an extensive blood test, so that you can verify for yourself the benefits of CR as they occur. Also, in an ideal world, you would want to calculate how many calories you are currently eating. This will add some useful precision, if others are to learn from your experience with CR—remember that you are a pioneer and that leaving a record is a good thing. But, unfortunately, I did not do the latter, so I have only a loose understanding of what percentage of CR I am engaged in at any particular time.
The range of recommended calorie restriction levels is from 10% to 25% from the unrestricted diet (Walford believes most people should start CR with 1,800 to 2,200 calories per day). But, you don’t want to lose too much weight and you don’t want to lose it too fast! A number of ways of thinking about CR have emerged. If you feel weak, lightheaded, or are overly tired and sleep a lot, you are either losing too fast or not getting enough nutrition with your reduced caloric intake—you should feel better, not worse, if things are going right.
To give a reference, it would be difficult for most people to lose more than a pound a week of true weight (ignoring water) in a healthy way. Since a pound loss (3500 calories, roughly) in a week breaks down to 500 calories per day, that is a quite substantial restriction (16.7% CR if one is initially at 3,000 calories a day, which is plenty of food). Note that the "Percent Daily Values" on all of the food packages these days refer to a 2,000-calorie diet, with gram numbers also being given for the 2,500 calorie diet. If you were eating at those levels before restriction, losing one pound a week would be 25% and 20% CR respectively. So, you are "safer" to take six weeks to lose 6 pounds, though this, too, is likely to vary with the individual. When I lost 12 pounds in that time (2 per week), I felt very bad, but Ray (another CR Society member) lost 15 pounds in 6 weeks and felt fine. The key is to be guided by how you feel--you are supposed to feel better, not worse. If you feel worse, lose more slowly. Remember that when you are losing fat you are also losing muscle along with that fat; you may also be releasing toxins stored in fat too rapidly.
Also, and especially if you are moderately to very active, you will find your fat percentage declining steadily as you lose weight. Walford believes that you should not let that fall below 6-10% for men and 10-15% for women. This is not terribly likely to happen for most people on CR—the 1990 mean values for males between 40 and 75 years old varied from 25.3 to 26.8% while the female means were 34.9 to 39.0% for those age groups! For men between 40 and 75, a 13 to16% body fat will put you in the lowest 5% of the nation, while for women, a 25 to 28% body fat will also make them leaner than 19 out of 20 people! And, we’ve gotten a bit fatter since 1990. So, it’s not too likely that you will acquire a dangerously low fat percentage. Despite Walford’s warning, having quite low body fat percentages may not be so terribly undesirable at least for particular individuals (Frank Shorter was estimated to be only 1-3% fat when he won the Olympic marathon in 1972!).
A rough measure of how fat people are is the Body Mass Index or BMI. This can be calculated by dividing your weight in kilograms (2.2 pounds to a kilogram) by the square of your height in meters (39.4 inches to a meter). Thus, if you weigh 150 lbs. (68.2kg) at a height of 5’9" (69" or 1.75m) tall and weigh 150 lbs., your BMI is 68.2kg/3.0625 = 22.3. Traditional nutrition/health sources say that the BMI for "normal" men and women should be in the range of 20-27, which roughly corresponded to the 10th and 75th percentile values in 1971-74. For a flavor of where you stand, from 1990 data (we’ve gotten fatter since then!), consider
|BMI||Adult Men (%)||Adult Women (%)|
I would guess that the average BMI of the members of the CR Society (a newsgroup on the web) would be well under 21, with many as low as 17. A recent study has indicated that those with lower BMIs are much healthier and less prone to disease and premature death than those with high BMIs.
While perhaps a depressing revelation for many, it turns out that you do not get CR’s health benefits by losing weight via increased caloric expenditure. It is true that a typical person could lose 1 pound a week either by restricting calories an average of 500 per day or by running 5 miles every day (losing an average of 100 calories per mile more-or-less regardless of speed) and eating the original number of calories. The reason exercise does not give CR benefits even if it gave equivalent CR weight stems from how CR is hypothesized to work. Food is the source of 90% of the oxidants or free radicals in the body—reducing food reduces oxidative damage. Exercise, ironically, actually contributes to free radical formation by burning that food faster. These negative effects are for most people (the non-CRers) more than offset by the health benefits of exercise, so that average lifespan is certainly increased by exercise. [Probably the oxidative damage is more than offset by positive effects of improved fat deposition, reduced obesity, and improved hormone status.] But a number of rodent experiments indicate that exercise doesn’t add anything to the maximum lifespan and fairly little to the average lifespan when animals are already calorie restricted. It is the CR that gives the benefits—exercise to feel better and to maintain independence in old age, but don’t exercise as a substitute for calorie restriction. Note, too, that while CR won’t make you stronger, it will make you relatively stronger—you’ll be able to do more push-ups and chin-ups, for example, just because you have less weight to lift! These benefits will be manifest in everything you do as you move around in your lighter body throughout the day.
Will a Longer Calorie-Restricted Life Really be "Better?"
In some respects, only you can answer that question. In economic terms, the answer may depend on your "internal rate of time discount," or perhaps what psychologists might call a desire for "immediate gratification" versus "deferred gratification." That is, if you find yourself really wanting things right now, rather than later, any perceived suffering now is not likely to be compensated for by having more years (of said suffering) in the distant future. People who smoke must obviously greatly discount the future, for example. But, so do people who run up charge cards that eventually must be paid for, and so do those who fail to save for retirement, as other examples.
As someone posting a note on a web newsgroup put it, "To me the whole calorie restriction thing is like the idea that you shouldn't drive your car, because people sometimes have accidents and crash into each other. So you can make your car live longer by not driving it, but where's the fun in that?" But, as someone responded on that same newsgroup, "The fun is that someday - perhaps within 30-50 years - science will be able to "roll back the aging clock" and make us all young again. And keep us that way. So we try to make our cars last until that day comes. Because then we can drive them forever." Those people, I would argue, will never understand each other because they have different rates of time preference.
CR, for many people, has some serious downsides that you should be prepared for, in the event they occur. You may be colder in your everyday activities (CR lowers body temperature usually, another possible mechanism underlying its anti-aging benefits). You may need to dress warmer or raise the temperature of your home to feel equally comfortable. The reactions of people you meet (they might think you look like you have cancer or AIDS or have an eating disorder) can be a problem. This is mostly a problem while you are in the process of losing weight; when you stabilize for a while they are likely to notice it less and less. Also fairly common are irritability and loss of libido (some of that may be offset by ingestible substances, but whether those substances might offset some of the benefits of CR is unknown at this time). Also, a recent concern in the CR Society newsgroup is that those on substantial CR might have more rapid bone loss than those on mild CR and ad lib eaters. The preceding issues may have an important effect on the degree of CR you wish to practice.
But, there are different "spins" on this issue. CR doesn’t really result in much suffering, if it is done properly--or at least it doesn’t for many people, including me. In particular, one can substitute along taste/nutrition/calorie lines to arrive at a meal that is equally pleasurable and filling to eat, but that has fewer calories and actually more nutrition. Moreover, there are other pleasures that come with CR that tend to offset any remaining "suffering," namely losing weight, feeling better, and being more attractive to others (subject to the caveat above). Too, remember that there are degrees of CR, and 10%CR is much easier than 25%CR. In fact, some feel that those starting CR in midlife (say, 40-50 years old) should practice more mild CR than might be desirable on longevity grounds for those starting as young adults. One might also begin with lower levels of restriction, find that it is not so difficult, and later increase the amount CR, gradually increasing the health and longevity benefits. To understand that, we need to get into how to practice CR:
How Does One "Calorie Restrict?"
As to background facts, proteins and carbohydrates have four calories per gram, while fats have nine calories per gram. For perspective, 4 grams of pure sugar is about one teaspoon and has 16 calories. A typical sweetened soda may be thought of as swallowing 9 or 10 teaspoons full of sugar! Similarly, the commonly mentioned 3-ounce serving of meat (at 28.35 grams to an ounce, that is 85 grams of meat) is approximately the size of a deck of playing cards.
If one is going to calorie restrict, you must reduce the numbers of grams of something…and, unless you reduce everything in proportion, the ratios of protein, carbohydrates, and fats will change. The current American average intake is 35% fat (12% saturated, 3% transfats, 14% monounsaturated, and 6% polyunsaturated—more on these breakdowns later), 50% carbohydrate, and 15% protein. In fact, virtually every diet variant (discussed later under "controversies") recommends a change from the current American eating pattern! But, this is also where the many diet controversies start in earnest, when compared as a baseline reference to the American Heart Association recommendations. For example, a (declining) number of people believe in very high carbohydrate and very low-fat diets (notably, Ornish), while others believe in moderately high protein and very high fat and very low carbohydrates (Atkins). Higher protein, less saturated fat, but more polyunsaturated and monounsaturated fats in the same overall fat intake, with lower carbohydrates roughly characterizes Sears, while Reaven recommends more mono and poly fats, with reduced carbohydrates. These approaches are discussed more fully in the "controversies" section later—CRers generally believe that almost any diet that is effective in reducing calories substantially will extend life greatly (provided nutrition is adequate), though momentum is growing in Sears' direction. I will "cut to the chase" and make recommendations that will certainly not be accepted by all, but that will provide a basis for later discussion of the controversies. These recommendations have come largely come from web discussions among members of the CR Society, tempered (or perhaps tampered) by my own views here and there.
Begin with your current, unrestricted diet (the so-called "ad libitum" diet in the case of the rats—what they eat when rat chow is freely available). The basic idea is to substitute foods that have more nutrition per calorie for foods that have less nutrition per calorie, while gradually reducing the number of calories. The goal is to get equal or better nutrition from fewer calories. This is not hard…as a practical matter, one should attempt something like the following:
Yet another way to think about diet under CR is to consider Paleolithic diets. The idea here is that mankind’s optimal diet (the one we have evolved to handle) does not include the "recent foods" that we only began consuming in large quantities in the last 5,000-10,000 years when agriculture began to replace the earlier hunter-gatherer system of food collection. In this view, the diet was mostly meat, non-starchy vegetables, and fruits—the meats eaten being mostly quite lean and everything eaten mostly raw. Stone Age people ate three times as much of a wide variety of vegetables and fruits as modern man. Vegetables and fruits (along with nuts, legumes, and honey) provided a rather astounding 65% of daily calories (with 100 grams of fiber). The remaining 35% of calories (2-3 times what is recommended in many diets today) was protein, largely from game animals, eggs, wild fowl, fish, and shellfish (along with the protein contained in the vegetables). Modern meat, especially red meat, has high levels of saturated fat—a more appropriate analogy to the type of meat eaten long ago would be skinless white meat poultry.
Contrast the modern American diet. It is argued that 55% of our modern diet is "new food" (cereal grains, milk, milk products, sugar, sweeteners, processed fats, and alcohol). Only 17% of calories currently come from fruits, vegetables, legumes, and nuts. And, 28% of calories come from fatty meats, domesticated poultry, fish, eggs, and shellfish.
Evidence indicates that the hunter-gatherers were healthier, with greater height (as suggested by the protein numbers above), better tooth retention, and longer life expectancy than was the case for the farmers, who arrived on the scene quite recently in evolutionary terms. Indeed, the life expectancy of paleo man was low compared to modern man only because of infections, injuries, and complications of childbirth…long-lived individuals without modern diseases of aging ("Syndrome X," coined by Reaven) would have existed in substantial numbers. There is debate about when farmers first domesticated animals and about when breads were made, and so on. But, on the whole, the story that we have evolved over the vast eons of time to eat mostly lean meat, vegetables, and fruits (with legumes and nuts) seems fairly compelling. The stomach/gut system in man would appear to be designed for omnivores, with the acids and enzymes to digest meat and fats along with considerable vegetable handling capacity. Under "controversies" some implications for vegetarianism are discussed.
Regardless of how one wishes to think of CR, however, success is fairly easily achieved by reducing mostly-empty calorie foods and especially increasing non-starchy vegetables and, to a lesser extent fruits (especially the berries). The plates you serve look more colorful and appetizing, too! The preceding is the "bare-bones" take on CR. You really should begin with a blood test and an examination of the calorie content of the foods you eat in a typical week. Just write down everything you eat on a pad of paper, and you can come back later to analyze how many calories it is. Otherwise, if you are like me, you will never be able to know what your CR is relative to your Ad Lib benchmark diet. You don’t have to do anything with that list for as long as you want—you may never care about all the "sciencey" issues. But, it’ll be there if you get more deeply into CR, as a great many people have.
The Diet "Controversies"
There are a number of controversies regarding CR, even among people who have been practicing it for many years. There are likely to be more such controversies, both that I am unaware of, and that will emerge as science progresses in the future. I will begin with the most controversial and important.
The table below compares the average American diet %ages with those
recommended by conventional medicine (the AHA recommendations) and various
|Diet Approach||Protein||Saturated Fat||Mono-Poly Fat||Carbohydrates||Cholesterol|
|American, actual||15||15 (3 trans)||20 (14 & 6)||50||300-400mg|
|Am. Heart Assn.||15||5-10||20||55-60||< 300mg|
* = calculated from Atkins recommended menus (no specific recommendations. Much of this information came from: Center for Science in the Public Interest, Volume 27 (no. 2), March 2000)
Interestingly, the actual American diet looks quite a bit like the AHA recommendations, with the exception of a bit more saturated fat and a bit less carbohydrates. Yet while Americans were moving closer to the AHA guidelines (more carbohydrates, less fat) between the late ‘70s and the early ‘90s, the obesity rate soared from 46% to 55%! So, while heart disease directly related to saturated fat’s role in clogging the arteries with LDL cholesterol has been declining, the extra weight (along with, more controversially, insulin and glucose swings) is likely to create a future epidemic of adult-onset (Type II) diabetes (with heart disease just occurring a bit later due to that!). Diagnosis: too much total food, as overall calories increased by some 200 per day over this period—cutting fat evidently caused total food intake to increase. Also, the carbohydrates consumed in the actual American diet are low-nutrient (potatoes in a myriad of forms, iceberg lettuce, bread, etc.), leading to major health problems due to their "crowding out" of vegetables and fruits that are vastly better for us. In addition, the carbohydrates consumed to excess are "high-glycemic" (tend to raise blood glucose more, and more rapidly, leading to undesirable insulin over-production--see Brand-Miller, Wolever, Colaguiri and Powell for more on the glycemic index). Note that high-glycemic carbohydrate diets are precisely how cattle are fattened in the feedlots of America (corn-fed)...reduced exercise and increased starchy carbohydrates are doing the same thing to Americans that we do to our cattle!
Atkins swings abruptly away from carbohydrates, but his diet is too overtly unhealthy due to the saturated fat (raising LDL cholesterol, hence increasing coronary artery diseases) and the failure to get enough phytonutrients from fruits and vegetables.
Ornish has a "total system" of weight loss, exercise, and meditation. It is a very demanding system that is difficult to follow, unless highly motivated (e.g. told that your arteries are about to close due to plaque formation, people might follow it!). It is probably a good plan for people with particular medical problems and has been shown to actually reverse plaque formation within arteries. If you can stay thin enough on this diet, it is probably fine for healthy people as well. You must, however, choose carbohydrates fairly carefully to maintain enough satiation to keep a stable weight and get the nutrients.
Reaven, however, believes that his plan would be better than Ornish’s because he claims that his diet would (under the same conditions of exercise and lost weight) be better yet because it would raise HDL levels and lower triglycerides, because of the increased emphasis on unsaturated oils. Reaven recognizes that there will be insufficient calcium in his diet and argues for a 500 mg supplement. In terms of medical professional qualifications, Reaven is vastly superior to the other competing diet authors, having authored over 500 scientific papers. But, his arguments appear most valid only for Ad Lib diets. Failing to consider what happens to nutrient intake when calories are restricted is, for me, the biggest problem with Reaven’s approach.
Any of the above approaches would likely be a substantial improvement over actual eating practices in much of the developed world. The difficulties come when one wishes to incorporate greatly reduced caloric intake into such diets. This is why Sears’ dietary approach has the greatest appeal among most CRers.
Sears program calls for increased protein, but with low saturated fat. Total fats come in at the AHA recommendation by increasing the mono- and polyunsaturated fat (see the Simopoulos and Robinson book for more on the important topic of fat). The big difference between the AHA recommendations and the Sears Zone is that carbohydrates are dropped to 40% from 55-60% to raise the protein percentage. Sears drops the carbohydrates by dropping the calorie dense but nutrient poor starches and sugars as described earlier.
Reemphasizing, probably all of the diets will work for many people, if they can lose weight on them and can enjoy them enough to maintain them as a life-style change, rather than as a temporary diet. Those who practice CR to improve and extend life, however, are attempting to go well beyond the goals of most dieters. CRers are attempting to eat 10-25% fewer calories than ad libitum feeding forever and will eventually get well below initial "setpoint" weight (the weight you tend to naturally be at, often what you weighed at around age 30). And, they want to do this without compromising their nutritional status.
A principal reason most CRers prefer the Sears approach is that when losing weight you lose more fat than muscle (particularly if moderately active). Hence you become a higher percentage muscle and a lower percentage fat (as Walford observed in the Biosphere II setting). Partly because of this, the consensus among CRers is that CR increases the need for protein, relative to non-CR diets. An ad libitum diet with 15% protein is probably fine for most people because the overall diets are excessive from a CR perspective (that is, 15% of 3000 calories is 450 calories and, at 4 calories per gram, is 112.5 grams of protein). With a 15% protein CR diet, too little protein is allowed in—the 15% becomes 15% of too small a number for the importance of protein to the human organism (15% of 1500 calories is 225 calories--only 56.25 grams of protein).
Expanding, without protein nothing moves in the human body. Protein is actually the second largest store of energy in the body, after fat; carbohydrates, despite their rapid availability, are depleted in a few hours of taxing activity. We certainly don’t want protein being used as a source of energy when there are important cellular processes to be done. The "official" recommended intake of "high-quality reference protein" (think of egg whites) is .8gm/kg/day. A 154 lb. man (70kg) should then be getting 56gm/day. That is not too terribly much—2 ounces a day (2/3 of a deck of cards worth of protein, if that protein is "reference" protein). But the case is more complex: First, there are the digestibility issues—is the body going to take in the proteins we actually eat as well as the reference protein? Second, and more important for most people, is the fact that proteins are created from 20 amino acids, of which 8 are "essential" (you can’t make the protein in your body unless they are present from the diet). Virtually all vegetable sources of protein are either incomplete or have percentages of amino acids that are not ideal for making human protein (they are after all plants, and don’t move—this is also the reason they don’t have, generally, any fat). Foods have to be mixed very carefully (though this is certainly possible, at least with an ad lib diet, a subject we’ll return to below) to get sufficient protein from non-animal sources. Animals are very much "more like us" in terms of the amino acids their protein is made of, hence protein insufficiency is rare in the developed world among non-vegans. In the most recent discussion of optimal protein intake in the CR Society, the consensus was that double the "official" recommendations would be better, 1.6g/kg/day. This is because the lower calorie intake might end up causing some protein to be used for energy, because we are a higher percentage protein per kg of body weight, and possibly to minimize any stresses caused by CR.
Returning to the Sears diet approach, by dropping, or substantially curtailing, the starches and sugars, one can actually increase the weight of the nutritionally dense, but low-calorie vegetables and fruits. This allows an increase in the percentage of protein taken in, as is optimal. Hence, you can get better nutrition, stay feeling full longer (from the generally low glycemic index vegetables and fruits), and enjoy your meals more. As a consequence, CR with the Sears approach doesn’t seem to involve as much "suffering" for most members of the CR Society. Additionally, the Sears Zone is by far the diet most closely related to the Stone Age diet discussed earlier, which may imply some evolutionary superiority.
It is certainly possible for an ad libitum eater to eat a healthy diet as a vegetarian…and they may even live longer than the typical ad lib eater of other diet types. But to a CR person who intends to live vastly longer than this, vegetarianism presents serious difficulties. Indeed, a few of our members were practicing vegetarians for many years, then converted to something closer to a Sears-type diet. As time went by as CR vegetarians, they began to get weaker and suffer an increased rate of disease. Interestingly, it may actually take quite a long time for this to happen. The reason is that the diet is only a one short-run source of protein…proteins of a wide variety are constantly breaking down in the body, providing raw input for the construction of new protein. In fact, only a little over a fourth of the daily use of protein in the "free amino acid pool" available for the formation of new protein comes from protein ingested that day (typically, only 90gm of a 340gm total). Since the 250gm of amino acids broken down from our innards must have just the amino acid balance we need, shortages in the diet may not manifest themselves for a long time. [Also, the vegetarian must be very concerned about Vitamin B12, which is very abundant in meats of various sorts, but quite difficult to obtain in sufficient quantities from a vegetarian diet. It would be wise to supplement at least this vitamin if you are contemplating a vegetarian diet.]
So here’s the bottom line: if we restrict calories and we’re vegetarians, there are not many opportunities to get enough of the right balance of amino acids, especially since CR people are likely to need more protein per kg of body weight. Japan currently has the longest average life spans in the world, but within Japan the Okinawan islanders who eat an abundance of animal seafood and many vegetables (and much less rice and other starchy foods) have the very longest average life expectancies. If on moral or other grounds you want to be a vegetarian, be very wary if attempting to gain the benefits of CR, too.
Role of Exercise?
As already mentioned, exercise has a certain dual nature. On the one hand, it increases the average life expectancy of those who exercise, among ad lib eaters. And, it is usually taken to be quality of life enhancing per se, to enjoy the functioning of a stronger body. But, it appears not to increase the maximum lifespan of CR rodents (the lifespans of the top 10%, say). The extra food eaten (and the exercise itself, as noted above) to maintain any given body weight will increase the formation of oxidants ("free radicals") that are partly blamed for the symptoms we observe as aging.
But, most of the people on CR do engage in at least moderate exercise. There are proven health benefits and quality-of-life concerns, that for most, offset what are minor CR negatives (the maximum lifespans of the exercised CR rats are nearly as long as the unexercised, and sometimes the average age at death is higher, despite not raising the maximal lifespan).
Raw vs. Cooked?
The raw versus cooked debate probably stems from a combination of two concerns. First, from the paleodiet versus "new foods" perspective, foods probably should not generally be cooked since the control of fire was a fairly recent invention (although that assertion is fairly controversial, too). Second, there is evidence of carcinogens being created in the cooking process.
On the other hand, there are some nutrients in certain vegetables that are better absorbed if cooked (carrots, spinach, etc.). And, there are heightened concerns with sanitation/pathogens for raw foods.
Overall, I would guess that most CRers eat a higher percentage of their food raw than does the general population, and the foods we do cook are usually cooked less long. Many CRers are quite fastidious (in terms of the contamination issue—see list discussions of grapefruit seed extract as a safe vegetable cleaner) and the knowledge that some foods are more nutritious cooked enables people to pick and choose what to cook. Ultimately, I think this is mostly an aesthetic issue—whatever tastes better at a particular time is likely to have a following. For example, sometimes I prefer bell peppers cooked, but at other times (and especially for the sweeter red ones) I eat them like an apple—quick, tasty and nutritious.
"Organic" vs. Traditional?
There has been considerable debate on this issue in the CR Society newsgroup. Some of the concerns are eco-system integrity, "dosage making the poison," natural versus synthetic pesticides and additives, and economic issues.
People are split on the issue of which would be better for the environment, organic or traditional (mono-culture, with artificial fertilizers and pesticides). One faction feels that the fertilizers are not sufficiently diverse and soils are being depleted (resulting in inferior nutrient content in traditional vegetables and fruits), while pesticides are believed to be likely to have dangerous, poorly understood eco-system effects that should be avoided (biomagnification, for example). The other side, believes that there is essentially no nutritional difference between the nutritional content of organic versus traditional foods (this is the position of The Berkeley Wellness letter, for example, and other "establishment" types). They also believe that broadly-applied organic methods would (because of lower yields, combined with the large number of animals needed to get the manure nutrients to put on the land) result in rapid habitat destruction, and indeed massive world human starvation if carried out on a large scale. There is an astonishing amount of fertilizer put on traditional crops, which would require extremely large amounts of any organic substitute…it must come from somewhere. Nobel laureate Norman Borlaug, who has arguably saved the lives of a billion people as a central figure in the green revolution, believes that converting to organic produce in a big way would be ecosystem destructive and would, moreover, likely kill hundreds of millions of people.
The "dose is the poison" and the natural versus man-made pesticides and additives issues revolve around how damaging low-dose pesticide residues are and whether the specific chemicals, some new to the human body, behave differently, from natural pesticides with which we co-evolved. Bruce Ames, well-known Berkeley expert, claims that we are exposed to 10,000 times as much natural pesticides as we are man-made pesticides, since plants contain many compounds designed to thwart the critters (usually small insects, parasites, and the like) that bedevil them. He argues that the chemical compounds are often quite similar in structure to artificial pesticides and that the liver evolved to handle a wide variety of new things. He notes that the few animal studies that examine cancer or mutagenic activity of commonly-consumed goods (e.g. coffee) have "flunk" rates about the same as the artificial pesticides in the same sorts of high-dose tests. Safrole, for example, is a powerful carcinogen and is abundantly present in ordinary black pepper. There are many such examples—the point is not to get you to stop using pepper! But, he argues (for both artificial and natural chemicals) that the liver has an amazing ability to detoxify the small amounts that we actually consume of most things. Others on the CR list are concerned about even small amounts of artificial additives, and prefer to eat organic foods. [On the other hand, I’d certainly rather be able to wash the pesticides off a vegetable than have a genetically modified vegetable that contained a pesticide that I would have to eat!]
The economic argument is related to the eco-system implications. If vegetables and fruits were to be grown organically, they are likely to be much more expensive (I think, as an economist, very much moreso than now, though there is disagreement about that on the list). If the price rises for things that are good for people, they will buy them in smaller quantities. And, it is those very vegetables and fruits that contain the phytochemicals that help us deal with carcinogenic compounds. We may become on net substantially less healthy (at considerable cost undertaken to make us more healthy, ironically), should organic foods displace traditional foods in a big way.
I’m frankly not sure what the "truth" is, though I personally almost always ignore the organic produce (mostly because it looks less fresh, like it isn’t selling as fast). Others on CR always try to buy organic when possible. I think much of it comes down to whether you like the taste of the organic better or don’t notice the difference and how much you are willing to pay for your food. It may not matter too much either way, since the CR immune system is better able to handle whatever goes into your body, in any event, relative to the ad lib eater.
Some CRers drink and some don’t. I won’t be discussing heavy drinkers; that is clearly unhealthy. For the ad lib eater, moderate alcohol consumption is almost certainly healthy (particularly red wine). But, the principal reason for that health effect may be that alcohol offsets the undesirable blood chemistry generated by the typical American diet. So, from a CRer’s perspective, those 7 calories per gram (yep, it’s an unusual carbohydrate that has more calories per gram than others—but doesn’t appear to act that way in terms of weight gain, for some reason) are just empty calories. On the other hand, quercetin, resveratrol, and other ingredients in red wine and to a lesser extent in red grape juice, have been demonstrated to reduce cancer. The consensus of the CR Society would likely be that, on net, it’s not worth it…but perhaps it doesn’t matter too much. Some use grape juice, but then you’ve got the sugars…. Moderation is, of course, key.
Supplements and other "potions"?
Here we have a real split among the CR Society group! Some feel that the increased vegetables and fruits (with the quality meats and proper fat profiles) render vitamin supplementation unnecessary. One person recently noted that he is using fewer pills over time as he continues with CR. The high nutrient density of the CR diet, combined with the internal body changes (lower temperature, some hormonal changes, etc.) are argued to guarantee more than 100% of the RDAs (even the recently modified ones that recommend more of several things).
Others (I’m in this group…but could possibly be swayed) take megadoses of vitamins and minerals and other "potions." The extensive discussion on the CR Society list of the many things that people take to increase their probability of extending their healthy years is beyond the scope of this introduction. See, however, Packer and Colman for the latest on anti-oxidant networks. Suffice it to say that some of us spend many thousands of dollars a year on "neutraceuticals," while the more typical CRer probably takes a complete (100% RDA) vitamin pill and perhaps a little extra C and E, and maybe some fish oil (or, better, flax seed oil). An interesting and informative place to begin if you are interested in going beyond CR, is the Life Extension Foundation (www.lef.org).
What about "glycemic index"?
Humans have a great many "feedback" mechanisms to keep our bodies functioning normally (e.g. to maintain temperature). Among those systems is the glucose-insulin feedback loop. When you eat, your digestive system eventually puts increased glucose in the bloodstream. Glucose is the fuel that runs the body, much like gasoline in a car. But, like a car, the fuel doesn’t "automatically" go into the cylinders from the gas tank, rather a precise set of operations result in the fuel injector injecting the fuel just when you want it to. You can drive a car without knowing anything about how that system works, just like you can practice CR without knowing anything about how it works! This material is a bit complicated, but I'll make it as clear as possible.
Imagine the impact of a lifetime of rapid starts and stops on your car--you are putting more total gasoline into the car and you are damaging your car in the process...it's "lifespan" will be shorter. Similarly, putting high glycemic index carbohydrates into you puts more total glucose into your system over your lifetime. It turns out that some of that glucose forms "cross-links" with proteins (called "non-enzymatic glycosylation") and that those cross-links are a prime cause of everything we think of when we think of "old people" (wrinkles, "liver" spots, stiffness, progressive stiffening of the arteries, etc.). Hence, putting more glucose into your body, results in more rapid aging other things equal (some people have genetic advantages, of course). So, you want to eat mostly low glycemic index foods.
The following is somewhat controversial, and some on-going research may soon clarify some things. The second reason many prefer low-glycemic index foods, is the relationship between glucose and insulin. As with the car, glucose doesn’t "automatically" go into the cells that use it for fuel, but rather the cells must be "opened" to enable the glucose to enter. When the feedback mechanisms of the body sense that glucose is elevated after a meal, a series of hormonal commands have the practical effect of increasing insulin in the bloodstream. It is insulin that enables the glucose to go into the various cells (muscle, fat, etc.) in the body. Insulin is, then, absolutely critical to the functioning of the body. But, with aging (and with excessive glucose intake, as CRers believe), the body gets progressively more resistant to the insulin—to do its job more insulin must be pumped out. The role of excess insulin in "causing" Type II diabetes is controversial, but some believe that too much insulin over long periods is a really bad thing. Excess insulin (hyperinsulinemia) is argued to increase body fat, mess with the balance of other hormones causing blood pressure to rise, reduce HDL (the good cholesterol), increase total cholesterol, etc. Perhaps, one of the reasons why CR extends lifespan, then, is by reducing lifetime exposure to insulin. This is all background for the "glycemic index" of foods, to which we turn.
The glycemic index is a measure, where either white bread or pure glucose is used as a reference point, of how rapidly and how much particular foods raise glucose in the body after being eaten (technically, it's the integral under the glucose concentration curve). In the context of the previous discussion, the glucose spike of a high-glycemic food will in turn create an insulin spike during which extra-normal amounts of insulin are produced (though the relationship between glucose and insulin is poorly understood, hence this is somewhat speculative). This exacerbates the problems discussed in the preceding paragraph. You may or may not feel hungry again sooner, but that is a common folk belief (e.g. hungry two hours later after Chinese food, due to the rice, if true). The "whites" (eating plain potato, white bread, or "sticky" forms of rice is almost exactly like eating pure sugar from a glucose creation perspective) and sugars already discussed tend to have high glycemic indexes (as do carrots and corn, interestingly). The glycemic index of the average of the food in the stomach determines the overall glucose spike to expect (hence, carrots and corn can go into a healthy stir-fry with lots of other vegetables, since that ameliorates their individual effects).
Most CRers tend to reduce the amount of high-glycemic foods they eat. Those that are eaten are mixed with items having a lower glycemic index to help even out insulin production, reducing the overall amount created.
As would be implied by the preceding, getting the same number of calories by, say, alternating days with no food with days with lots of food, is likely to result in a greater total creation of insulin, than eating more evenly. It is probably the case that an essentially continuous nutrient flow is the best way to even blood glucose and minimize insulin output. On the other hand, it is also the case that many CRers find that they can’t really effectively practice CRer without something like fasting going on. Indeed, "break fast" (the origin of our breakfast) is not eaten by some CRers, because they find it makes them hungrier for lunch. The lesson, I believe, is that it is more important to practice CR effectively, with how one is able to succeed at it being secondary. We know that if less glucose-creating food goes in, less insulin gets created.
As one of the CR Society members (Warren) put it so well:
The successful voluntary practice of CR in humans is
1) the life-long focused commitment
2) to gain knowledge, self-control, and motivation
3) to reduce calories consumed,
4) while maintaining adequate nutrition,
5) under active monitoring of current state of health,
6) with the hope of living better,
7) and the hope of living longer.
That's really it in a nutshell.
Scientific learning is an on-going process, yet we have to make decisions today. The following captures what many of us are doing in practicing CR in a world where all the information we'd like to have is not currently available:
"Life is the art of drawing sufficient conclusions from insufficient
premises." -- Samuel Butler
Atkins, R.C. Dr. Atkins New Diet Revolution, M. Evans, January 1999.
Austad, S. Why We Age: What Science is Discovering about the Body's Journey through Life, Wiley: New York, 1997.
Brand-Miller, J, T.M.S. Wolever, S. Colagiuri, and K. Powell, The Glucose Revolution, Marlowe and Company: New York, 1999.
Center for Science in the Public Interest, Nutrition Action Health Letter, Vol 27, no. 2 (March 2000).
Packer, L. and C. Colman, The Antioxidant Miracle, Wiley: New York, 1999.
Reaven, G. Syndrome X: Overcoming the Silent Killer that Can Give You a Heart Attack, Simon & Schuster: New York, 2000.
Sears, B. The Anti-Aging Zone, Regan Books (imprint of HarperCollins Publishers): New York, 1999.
Shils, M.E., J.A. Olson, M. Shike, and A.C. Ross, (eds) Modern Nutrition in Health and Disease, 9th Ed. Williams and Wilkins: Baltimore, 1999.
Simopoulos, A.P. and J. Robinson, The Omega Diet, Harper Perennial: New York, 1999.
Walford, R.L. Beyond the 120 Year Diet: How to Double Your Vital Years, Four Walls Eight Windows, 2000.
Walford, R.L. and Walford, L. The Anti-Aging Plan, Four Walls Eight Windows: New York, 1994.