Just consider for one moment what you would do if you heard that scientists had found a way of extending the human life span. Not just extending it, but also allowing you to maintain youthfulness and vitality for most of your later years. What would you do? Immediately go out and start taking the supplement? Or wonder drug? Or super food? But there's more! Whereas purchasing the various products in health food stores that fraudulently claim to do just that will empty your pocketbook, this approach will actually save you money. No, it's not a magic pill at all. It's something called dietary restriction. Yes, it involves lifestyle change. But don't let that scare you off. With the right frame of mind, you can do more than you think. More about that later.
Dietary restriction, also known as caloric restriction, simply means watching your calories and eating less. Studies involving all kinds of animals, from worms and insects to mammals like us, have uniformly shown that consuming fewer calories can lessen the risk of many chronic diseases and extend the upper limits of life expectancy.1 Consuming less fat but taking in the same number of calories does not have the same effect. Ditto for protein, even though we know that excessive protein can also be harmful. And the same for carbohydrate, whether we're talking about complex carbohydrate (starch) or simple carbohydrate (sugar). The cut in calories is generally at least 30% below the amount consumed when an unlimited food supply is provided. The key to dietary restriction, though, is that adequate amounts of all nutrients, such as protein, vitamins, and minerals, are consumed. It is not a deficient diet in any respect and does not lead to malnutrition.
Why have all of these studies been performed on animals other than humans? The reason is that humans have such a long life expectancy that it would take the greater part of a century to determine whether the upper limits for life span were really being extended, assuming that the dietary restriction was begun in childhood. The problem with using animals, though, is that the results cannot be uncritically extrapolated to humans. What occurs in some species of animals may not occur at all in humans. Many nutrition studies on rats, for example, regarding protein and other requirements, have misled us because humans are so different. How many times have you heard of some major study on animals that seemed to promise that a cancer cure was just around the corner? Then you never hear anything about it again. But the fact that the benefits of dietary restriction have been seen in virtually all animals studied would suggest that the phenomenon represents a common thread of all life and therefore applies to humans as well.
The studies on mice and rats have shown that dietary restriction does not even have to begin in childhood. Cutting back on calories in mid-life is almost as effective in extending life span as beginning the diet in childhood. If dietary restriction works on humans the way it does on other mammals, then that's good news for us. Further, the studies on mice indicate that less dietary restriction with increasing age is desirable. Consuming more calories in the later stages of life (but still restricting them somewhat) results in the maximum extension of life. It's not clear why this should be. Perhaps it is related to reduced absorption of certain minerals or other nutrients with age, or perhaps it is due to a change in metabolism.
Animals who are on the lower calorie diet tend to be leaner than those who are not restricted, as expected. But those allowed to eat all they want are usually not obese, so we cannot attribute the lower life expectancies of the unrestricted animals to the health risks associated with obesity. Further, among those mice who are having their calories restricted, the heavier ones tend to live the longest! One possibility is that the mice who become heavier are those who use the calories they consume most efficiently. Less efficient use of calories may result in the production of harmful by-products of metabolism such as free radicals -- activated forms of oxygen and other molecules that can damage the body's cells and their contents.
What about exercise? Rats who voluntarily exercise in a wheel and eat a regular diet burn up enough calories that their net calorie intake is the same as that of non-exercising rats on restricted diets. Yet they do not live as long as the rats on the reduced calorie diet. Obviously, there is something about eating less that makes the difference. But don't assume from this that exercise does not promote health and increase longevity, at least in humans. A number of studies have shown that becoming physically fit does indeed reduce the mortality rate in people. The benefits of regular exercise and avoidance of a sedentary lifestyle have been touted by physicians throughout history.
Preliminary results in monkeys indicate that they also live longer on a calorically restricted diet. But we have little information about humans. Few people would want to cooperate with a study that would go on for such a long time. Observing groups of people in the world who currently consume fewer calories is not very productive because such populations often consume diets that are deficient in various nutrients.
One interesting report by Dr. Yasuo Kagawa concerned nutrition and the longevity of the Japanese following World War II.2 He found that those who lived on the island of Okinawa, where, on the average, people consumed 17% fewer calories than those on the mainland, were about 40 times as likely to live to be a hundred years old as people who lived in the northeastern prefectures of Japan. Very few people on Okinawa experienced serious disease before age sixty.
Another report described a three-year study involving retired members of religious institutions.3 They normally consumed about 2,300 calories a day. But the restricted group got only a quart of milk and a pound of fruit every other day, equivalent to about 1,500 calories. This group required health care less frequently than the unrestricted group, and there was a trend toward a lower death rate as well. A longer study may have shown a much greater difference between the two groups.
A small number of healthy people participated in a study4 by allowing themselves to be sealed inside an enclosed space called Biosphere 2 near Tucson, Arizona. Their food availability was greatly restricted during most of the two year period. Their cholesterol and triglyceride levels plunged by 30% and 45% respectively. Their blood pressures and blood sugar levels also declined significantly while they were involved in the experiment, lending support to the findings observed in nonhuman animals undergoing dietary restriction.
In 2004, researchers at Washington University in St. Louis reported findings on 18 adults who had followed a calorically restricted diet for an average of 6 years.5 Marked drops in cholesterol and triglyceride levels, blood pressure, blood sugar and insulin levels, and C-reative protein, a marker of inflammation in the body, as compared with a group of people following the usual Western diet, were all observed. The calorically restricted group was following what we would consider a qualitatively more healthful diet than the other group as well, so we cannot attribute all of the findings to the restriction of calories.
The Washington University group published another study on 25 calorically restricted individuals in 2006.6 They found that this group had heart function similar to that which would be expected in people fifteen years younger. Again, the participants were consuming a healthful, Mediterranean style diet, but the study provides one more piece of evidence of how diet can significantly retard aging changes in the body.
The studies indicate that the benefit of dietary restriction goes beyond mere extension of life. That is very important, because the quality of life is probably more important than the length. We sometimes say that the goal is to die young as late in life as possible. And that is what happens to mice and rats on this kind of diet. They not only live a long time, they also tend to be healthy, lean, and active for most of their lives.
Dietary restriction may help prevent some chronic diseases, and it may also contribute to a more favorable prognosis in people who already have certain diseases. Chronic diseases are those that tend to increase in frequency with age and for which there is often no cure.
Many of these studies have looked at breast cancer in mice and rats. For example, in one strain of mice in which many fatal mammary cancers appear after ten months of age, none of these cancers developed in mice that were underfed. Other studies on the Wistar strain of rats showed that those eating ad lib had five times as many mammary tumors as those on a restricted diet, and the tumors in the latter rats tended to be smaller. Studies involving mice yielded similar results.
Why do so many women in Western countries develop breast cancer? For some time, it was the number one cause of death due to cancer in women. Now it is second only to lung cancer. Fatal breast cancer is ten times more frequent in American women than in Japanese women following a traditional non-westernized diet. The explanation has been elusive. We can't blame it on genetics even though there are hereditary tendencies for most diseases. The fact that the rate of breast cancer has increased dramatically in Japan following the introduction of Western lifestyle practices suggests that diet plays an important role.
You may have heard of the "dietary fat hypothesis." The idea here is that the high-fat American diet greatly increases the risk of breast cancer. The average American diet derives 40% of calories from fat, compared with 10% or fewer in a traditional Japanese plant-based diet. But there are many differences other than fat between the two diets, and recent studies have not strongly supported the dietary fat hypothesis, so it remains controversial. Since fats are involved in the production of sex hormones, and since breast cancer is a hormonally related cancer, it is still possible that fat plays a role. But it is very hard to make a definite determination by studying only Americans, since the number of people in the U.S. who follow a Japanese-style diet is minuscule.
The dietary restriction studies we've discussed, however, suggest another important risk factor for breast cancer -- eating too much. We already know that people who are overweight are at higher risk, so it makes sense. The number of calories consumed is obviously not totally independent of fat, since fat is very high in calories and people who consume a lot of fat are usually consuming more calories than other people. Let's take another look at Dr. Kagawa's figures in his study of Japanese women. In 1975, even after westernization of the Japanese diet had progressed to a considerable degree, a Japanese woman, on the average, consumed about 2,467 calories a day. Compare that with the United States, where the per capita calorie intake was 3,304 calories a day. The Japanese women were consuming about 25% fewer calories than the American women!
Studies of Norwegian women also provide support for the concept that too much food is a culprit. Those who went through puberty during World War II, a time when food was restricted, subsequently had a lower risk of developing breast cancer, despite the fact that their menstrual periods began at the same age as women who lived earlier or later. Further studies showed that the protective effect was most prominent in those areas of Norway where food was the scarcest. Naturally, there were other wartime differences in diet besides the number of calories, but the studies do provide some support for the theory that dietary restriction can lower the risk.7
Dietary restriction has reduced the incidence of a number of other common tumors in mice and rats. Again, whether it would show any benefit in humans remains to be determined. One human tumor for which dietary restriction should be investigated is prostate cancer, another hormonally dependent tumor. It is second only to lung cancer as a cause of death in American men, and the rate is about ten times higher in American men as in Japanese men on their traditional diet. On a microscopic level, elderly Japanese men have just has much prostate cancer as American men do, but, in Americans, the cancer tends to be more aggressive. Fat may play a role here, as some studies have indicated that fat consumption correlates with tumor aggressiveness. Meat and dairy product consumption may also increase the risk. But certainly we should determine whether consuming too many calories plays a role.
Immune system problems are also being investigated. Although the immune system generally becomes weaker with age, it can also undergo the derangements seen in autoimmune diseases. In these disorders, the immune system of the body attacks some of the body's own tissues instead of infectious agents like viruses and bacteria as it is supposed to. Three common autoimmune diseases are rheumatoid arthritis, lupus, and multiple sclerosis. Inflammation in general, which also involves the immune system, is being increasingly implicated in problems ranging from heart disease to Alzheimer's. Diet may play an important role in lessening the severity of these problems, and dietary restriction is just one of a number of possible approaches.
A number of strains of mice are prone to autoimmune diseases resembling lupus, more formally known as systemic lupus erythematosus, or SLE for short. Lupus is a disease that can cause arthritis, kidney problems, vasculitis (blood vessel inflammation) in the brain, and many other disorders, and it can markedly shorten life expectancy. In a number of studies, dietary restriction has been shown to improve the condition of lupus-prone mice and dramatically increase their life span. Benefits can be seen not only when dietary restriction is started early in life but also in adult mice. Dietary restriction, therefore, has a therapeutic (and not just a preventive) effect. Immune-related problems with the kidneys occur to a much lesser degree in these restricted mice regardless of the age at which it is begun. Other autoimmune diseases affecting the kidneys are benefited as well. In some strains of mice, signs of autoimmunity such as anti-DNA antibodies and immune complexes increase with age, but dietary restriction seems to block these increases.
We already have good evidence that alterations in diet can help people who suffer from rheumatoid arthritis. It has long been known that fasting causes a temporary decrease in joint symptoms. Fasting, of course, is a form of dietary restriction. Dr. Kjeldsen-Kragh and his colleagues at the University of Norway showed that a vegetarian diet can be very effective in reducing both the signs and symptoms of rheumatoid disease.8 Of course, there are other factors besides the number of calories in a vegetarian diet that might be beneficial. Vegetarian foods are lower in the kinds of fats that lead to inflammatory substances in the body. They are richer in phytochemicals, which are plant-derived substances that often have anti-inflammatory properties, than meat-based diets. And they seem to alter the composition of the bacteria that live in the large intestine, a phenomenon that may also be helpful. One case report in the British journal The Lancet described a woman with lupus whose symptoms remitted when she tried a vegetarian diet.
Another chronic disease that has the potential to be helped by dietary restriction is diabetes, and we will discuss that later when we examine some of the specific changes that can be measured in the blood of animals or humans whose food intake has been curtailed.
One thing is clear. If we are ever to determine whether the aging process in humans can be slowed down by dietary restriction, we must find a better way of studying it. Carrying out a study for the entire life of a human is impractical, and we cannot assume that the results on short-lived animals are in any way applicable to us. Fortunately, there is a way of getting around this dilemma.
If we can simply measure the rate of aging over a relatively short period of time, say two or three years, we would then be able to predict the effect on our maximum life span. As everyone knows all too well, there are definite signs associated with aging -- wrinkles, graying of the hair, drooping, etc. But we need to be a little more scientific than that. Scientists have been attempting to develop a list of certain age-related changes in the body that could be used to determine the rate of aging. These are called biomarkers of aging. Many of these are simple blood tests. What are the characteristics of a good biomarker? First, it must be reproducible. This means that when you repeat the test right away, you get approximately the same result. Second, measurement of the biomarker should not harm the person or animal. Third, it should change predictably with aging so that it can be used to determine the rate of aging and the estimated life span. Fourth, the changes should occur over a relatively short time so that the study is not unduly prolonged. Finally, it should reflect a function that has a direct bearing on health. Studying these biomarkers of aging may also help us determine just how dietary restriction prolongs life, although determining that it does is more important than knowing how it does it.
We will now look at many of the bodily changes induced by dietary restriction and explore their significance. Some of these, either alone or in combination, may represent the key to the fountain of youth.
Dietary restriction lowers the metabolic rate, at least in the short term, in monkeys as well as in mice and rats. This means that the fuel-burning chemical reactions in the body are slowed down. The important thyroid gland hormone T3 is lowered with both short- and long-term dietary restriction, and this contributes to the slowed metabolism. Whether this lower metabolic rate is one of the mechanisms by which dietary restriction increases life span remains controversial. But why should it increase life span? The theory is that the burning of fuel for energy in the body occurs in the mitochondria, which are the powerhouses of our body's cells. As you know, fires require oxygen to continue burning, and the cells of our body do also. The process can result in the formation of activated forms of oxygen and other molecules that we call free radicals. Free radicals can attack important components of the cells, such as DNA, proteins, and the cell membrane. We strongly suspect that this kind of damage is a cause of aging and chronic diseases such as cancer.
There is evidence to support this theory. Rats undergoing dietary restriction have been found to have reduced levels of activated forms of oxygen in the mitochondria of their livers as well as reduced oxidative damage to the DNA in the mitochondria. The fact that the larger diet-restricted animals are the ones who live the longest also supports this theory, since it suggests that they are the more efficient fuel burners, thereby producing less of the harmful activated oxygen by-products.
A lower metabolic rate may also help people who already have cancer. Since cancer cells divide much more rapidly than normal cells, they require more energy to accomplish this. If people with cancer reduce their calorie consumption and their metabolism becomes slower, the cancer cells can be expected to suffer. Their growth will be inhibited and they may even die off. Therefore, the concept that cancer patients should eat more and put on weight while they can may be wrong. It's true that they'll have farther to go when they reach the late stage of their disease and start losing weight. But consuming more calories may actually be helping their cancer cells to multiply more rapidly.
Lower body temperatures are one of the most consistent findings in animals on dietary restriction. This may well be linked to the lower metabolic rate, but it appears doubtful that the lower temperatures have any direct effect on slowing the aging process.
Insulin and blood sugar levels are lower, with increased sensitivity of the body to the actions of insulin in monkeys as well as rodents. This is a very important finding, since resistance to the effects of insulin results in diabetes in adult humans, especially those who are overweight. This insulin resistance syndrome is associated with a wealth of other problems, including high cholesterol and triglyceride (fat) levels, high blood pressure, and heart disease. Some theorize that the high insulin levels in themselves may cause or contribute to these other problems. Both lowered tryglyceride levels and lower blood pressures occur in calorie-restricted monkeys. In addition, HDL-cholesterol, the "good" cholesterol, is increased. The good news is that lower insulin levels occur very quickly after dietary restriction is begun. This may explain why some people can enter a lifestyle program and depart two weeks later leaving some of their diabetic or blood pressure medications behind.
Insulin-like growth factor 1 (IGF-1) is also lowered by dietary restriction, not surprising since it has long been known that reducing either total calories or protein has this effect. IGF-1 is a polypeptide (protein-like) growth factor that causes many kinds of cells to proliferate. It has been linked with a number of human cancers, including those of the breast, prostate, colon and rectum, and thyroid. This could well be one of the reasons why so many of the dietary restriction studies have shown fewer and less aggressive tumors in those animals undergoing dietary restriction. Preliminary studies also show that low calorie intake may reduce angiogenesis, blood vessel growth that feeds tumors, and increase apoptosis, programmed cell destruction that can eliminate cancerous cells.
Repair of DNA is increased by dietary caloric restriction. Since DNA is constantly undergoing oxidative attack by free radicals and other activated forms of oxygen, there is a need to repair the damage. Facilitating the repair mechanisms could have a positive effect on aging and possibly even prevent the development of cancer. Protein turnover is also increased. This means that the body is synthesizing more protein and replacing proteins that have become damaged. This may also be important because protein turnover declines with age, allowing damaged proteins to build up in our cells. Although we are not certain whether this is a cause or a consequence of aging, helping our body replace defective proteins with new ones may have an anti-aging effect.
Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are steroid hormones produced by our adrenal glands. They are intermediates in the pathway that leads to the formation of both male and female sex hormones. Their levels in the bloodstream gradually decline as people age. Some studies have shown a higher mortality rate (death rate at a given age) in men with lower levels of this hormone. This does not prove, of course, that the lower levels caused them to die earlier. Many animal studies have suggested that DHEA may slow down aging, boost the immune system, and even prevent cancer. The problem is that very large dosages of DHEA were used, and most of the animals studied were rodents, who have hardly any DHEA and DHEAS to begin with. As often happens, inappropriate extrapolation of these results to humans has led to DHEA's being touted as an anti-aging miracle, and many people have obtained the hormone, a "natural supplement," from their local health food stores. There is concern, however, that these supplements might have adverse effects, such as promoting the growth of hormone -dependent cancers, among other things. In any case, dietary restriction blunts the decline of DHEAS in monkeys as they become older, and it is possible that this may be one of the factors that enables them to remain youthful longer.
Interleukins are small proteins that have an effect on immunity and inflammation. Some but not all studies have shown a decline in interleukin-6 levels with dietary restriction. Interleukin-6 leads to the formation of C-reactive protein, which is a sign of inflammation. A low-calorie diet and weight loss have been shown to cause a decline in C-reactive protein in overweight people. This is important because reducing inflammation might help people with autoimmune diseases. It may also help prevent or improve some of the other diseases in which inflammation is now felt to play a role. The most common of these is coronary artery disease, which leads to heart attacks. Since blood levels of C-reactive protein can predict the risk of heart attack, lowering C-reactive protein levels by dietary restriction may, along with lowering of cholesterol levels and other treatments, help prevent coronary disease, the most common cause of death in the United States.
In summary, dietary restriction can change the body chemistry in many ways, and it is probable that many of these changes can lead to improved health and increased longevity. Choosing appropriate biomarkers of aging will allow good studies to be performed on humans. We need to determine not only whether calorie cutting does indeed add quality years to our lives, but also the ideal number of calories to consume at the different stages of life. At the same time, we cannot forget that the quality of the foods we eat is also important, and the other chapters of this book are devoted to that subject. But since we already know that overeating is harmful, and since most of us tend to be overeaters, the question now is how to cut back on the amount of food we're eating without diminishing the joy of eating.
All too often, health professionals make dietary recommendations based on what they think people will accept rather than on what would be best for them. They doubt the ability or willingness of people to change their ways. For example, I am sometimes reading a study touting the benefits of a high-fat diet and am puzzled as to why anyone would recommend this over a healthy, low-fat diet. Then, somewhere toward the end of the article, I come upon a grudging acknowledgment that low-fat approaches have done even better but would be unacceptable to the masses because of their "unpalatability." There is no conception whatever of the possibility that people can change their tastes with appropriate counseling and encouragement.
Recently, one of the main groups of researchers involved in dietary restriction studies declared that it was very doubtful that humans would ever agree to consume fewer calories even if they knew it would mean a longer and healthier life. The researchers did not want to recommend anything that would interfere with the pleasures of eating, even though eating less food, if done properly, can be equally enjoyable. In fact, compared with the very transient pleasure experienced with overeating, moderation in one's eating can result in a much deeper, longer lasting pleasure when it is part of a moderate lifestyle. Thus, these researchers were looking for drugs or other substances that might mimic the beneficial effects on health seen with dietary restriction. This approach lies in clear opposition to the philosophy of those of us who believe in the importance of trying to change oneself for the better. There is no magic bullet or easy shortcut. A return to the proper path is the only answer.
We can make a number of suggestions to help you limit your food intake. There is no need to starve yourself. On the contrary, eat when you are hungry and stop eating before that feeling of fullness comes upon you. Then leave the table to avoid the temptation to eat more.
Most people who engage in compulsive eating have lost touch with their body's signals. When you do attempt to pay attention to what your body is telling you, and you start to experience feelings of hunger, that will be positive reinforcement for you that you are on the right track. One can also meditate on the fact that the hunger leads to the eating that, when properly performed, provides spiritual as well as physical refreshment for our bodies. When you reframe hunger in your mind in these ways, it can become a pleasant reminder of how well you are succeeding with your diet instead of an unpleasant sensation.
The urge to eat when one is not hungry is often the result of emotional stress. Mild depression or boredom can also fuel the habit. Find other ways of dealing with stress. Try going for a walk or engaging in other exercise. If you do feel the need to satisfy your oral urges, try just drinking water or eating some low calorie snacks.
When you do decide to snack on a particular food, don't assume that you need to consume a great deal of it in order to enjoy it. It is the quality of the experience, not the quantity, that is important. When chocolate was introduced to Europe several centuries ago, it was a precious and rare treat that could be afforded mainly by the aristocracy. Expensive porcelain and silver cups were designed to enhance the experience. Think of all the pleasure people had back then as they savored just a little bit of their chocolate drink. If you think of your food in that way, you will enjoy it all the more.
Make use of all your senses. Savor the appearance and smell of what you're eating. Place just a little bit in your mouth at one time and allow it to stay there for several seconds. Experience its taste and texture. Slow down the whole eating process. You will probably begin to enjoy eating all the more. Your taste and smell will become more acute. Cut back on the oils and other fats and you will experience tastes you never knew existed. You will notice the sweetness in an onion and not just the pungency. The clean, fresh taste of vegetables will come through.
Altering your buying habits can help as well. If you see something in which you know you will be tempted to overindulge, simply buy less of it and avoid the temptation. Sometimes I see some beautiful cherries or strawberries in the store but am hesitant to buy them because of the price. Rather than do without, I just buy fewer of them -- perhaps just eight or ten cherries, for example. As with the story of chocolate, if you regard something as a rare commodity, you will experience pleasures you never dreamed possible from even small amounts. Spiritually oriented people who are able to see the holiness in food and in the eating process will experience much of the same kind of enjoyment from eating.
You know your own weaknesses. If there is some snack food that makes it impossible to resist the temptation to eat "just one," don't buy it. If you do buy snack foods, put them out of sight and thereby out of mind.
Some people resolve to just eat half of what is on their plate, even though that seems like a terrible waste. I prefer to simply dole out a much smaller portion to begin with. The remainder then goes right in the refrigerator so it isn't there to tempt me after my plate is emptied. Studies have shown that when people are served smaller portions, they tend to eat less and don't usually bother getting second helpings.
How much should you be restricting your diet? At this time, I can only recommend eliminating the excess calories that you consume as a result of overeating, for example, your tendencies to continue eating even when you are full and to eat at other times when you are not really hungry, and so on. Obviously, if you are sick and have no appetite or if you are diabetic and have to eat on a set schedule, you need to eat regardless. But here I'm talking about people who are generally healthy. We don't yet know whether dietary restriction, performed to the degree employed in the animal studies, will be beneficial to humans, so I don't recommend restricting yourself to that degree.
A low-fat, high-fiber diet is really the ideal way to cut back on calories, because fat contains more than twice the number of calories per gram or ounce as carbohydrate or protein does. Studies have shown that diets high in fiber and low in energy density (calories) induce satiety (sense of fullness) equal to that of diets providing more calories. That doesn't mean you can't eat some foods that are relatively high in fat. For example, nuts consumed in moderation are good sources of vitamin E and other beneficial substances. It does mean that you should try to get out of the habit of cooking in oil (using water or vegetable broth works fine) and smearing high fat spreads on your toast and bagels. It's very easy to get over the taste for fat once you cut most of it out of your diet. As a child who was used to drinking whole milk, I recall disliking the watery taste of the skim milk my grandmother used to drink. When I was older and was trying to improve my diet by cutting back on cholesterol and saturated fat, I switched to skim milk for my cereal. After a short while, the taste of whole milk became unpleasant because of its richness. When I finally eliminated the dairy and began using soy milk, which had a moderate fat content, even that seemed rich at first and I had to dilute it with water. Soon, it tasted just fine undiluted. Therefore, our taste for fat can be changed very readily.
It's true that some of the faddish low carbohydrate higher fat diets are low in calories. But we need to be concerned about the quality of the foods we're consuming as well, and most of the foods rich in health-promoting phytochemicals and antioxidant vitamins are those that are rich in complex carbohydrate (starch). We're talking about members of the plant kingdom, of course.
If you do restrict your food intake a great deal in order to lose weight, remember how important it is to make sure you are getting a sufficient amount of all the nutrients. The successful dietary restriction studies all contained adequate amounts of vitamins, minerals, and protein. Therefore, a low calorie diet for weight loss should emphasize foods that are nutrient-dense. What do we mean by that? We don't mean foods with the most nutrients per unit weight or volume of the food. We mean the most nutrients per calorie. That is a very important distinction, because the healthy vegetables that we should be emphasizing in our diets actually stack up very well against animal products when we look at nutrient density from a per calorie basis. As an added bonus, they have none of the cholesterol and much less of the saturated fat.
Compare the dark, leafy green vegetable kale with reduced fat (2%) milk, for example. Using the latest figures from the USDA Nutrient Data Laboratory, we find on a per calorie basis that kale has more protein, calcium, and zinc, severalfold more magnesium, copper, and potassium, 5 times more essential fatty acids, 20 times more vitamin E, 32 times more iron, 73 times more vitamin C, and over 350 times more manganese! It also has manyfold more vitamins B1 (thiamin), B3 (niacin), B6 (pyridoxine), and folate, a little less vitamin B2 (riboflavin), and is lacking only in vitamin B12 (cobalamin). Now add on all of the fiber and the numerous phytochemicals with their antioxidant, anti-inflammatory, and cancer-preventive properties, none of which you'll find in milk. Which would you say is the more nutrient-dense? Similar analyses can be made on many other vegetables. We will discuss the ins and outs of achieving optimal nutrition more extensively in the final chapter.
Numerous studies over the past half century have consistently shown that restricting calories while maintaining nutritional adequacy extends life span, lowers the risk of chronic disease, and improves vigor and vim in a wide range of animals. Potentially beneficial mechanisms of this approach include a slowing of the body's metabolism, lowering of blood sugar and insulin levels, reducing the rate of decline of the steroid hormone DHEAS, and exerting a favorable influence on levels of fats in the bloodstream. Although we do not know the degree to which human health and quality of life would be improved, we already have enough evidence of the harmful effects of overeating to recommend that eating habits be improved.
1Weindruch R, Walford RL. The retardation of aging and disease by dietary restriction. Springfield, Illinois: Charles C. Thomas, 1988.
2Kagawa Y. Impact of westernization on the nutrition of Japanese: changes in physique, cancer, longevity and centenarians. Prev Med 1978;7:205-217.
3Roberts SB, Pi-Sunyer X, Kuller L, et al. Physiologic effects of lowering caloric intake in nonhuman primates and nonobese humans. J Gerontology: Series A 2001;56A:66-75.
4Verdery RB, Walford RL. Changes in plasma lipids and lipoproteins during a 2-year period of dietary restriction in Biosphere 2. Arch Intern Med 1998;158:900-906.
5Fontana L, Meyer TE, Klein S, Holloszy JO. Long-term calorie restriction is highly effective in reducing the risk for atherosclerosis in humans. Proc Nat Acad Sci 2004;101:6659-6663.
6Meyer TE, Kovacs SJ, Ehsani AA, et al. Long-term caloric restriction ameliorates the decline in diastolic function in humans. J Am Coll Cardiol 2006;47:398-402.
7Robsahm TE, Tretl S. Breast cancer incidence in food- vs non-food-producing areas in Norway: possible beneficial effects of World War II. British J Cancer 2002;86:362-366.
8Kjeldsen-Kragh J, Haugen M, Borchgrevink CF, et al. Controlled trial of fasting and one-year vegetarian diet in rheumatoid arthritis. The Lancet 1991;338:899-902.