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Chapter One: Human Nutrition: An Evolutionary Perspective
In order to answer the question "What is a healthy diet?," it is important to first take a look at what our body is designed for. Is the human body designed to eat plant foods, animal foods, or both? Respectively, are we herbivores, carnivores, or omnivores?
While the human gastrointestinal tract is capable of digesting both plant and animal foods, there are indications that we evolved to digest primarily plant foods. Specifically, our teeth are composed of twenty molars, which are perfect for crushing and grinding plant foods, along with eight front incisors, which are well suited for biting into fruits and vegetables. Only our front four canine teeth are designed for meat eating, and our jaws swing both vertically to tear and laterally to crush, while carnivores' jaws swing only vertically. Additional evidence that supports the human body's preference for plant foods is the long length of the human intestinal tract. Carnivores typically have a short bowel, while herbivores have a bowel length proportionally comparable to humans'.
To answer the question of what humans should eat, many researchers look to other primates, such as chimpanzees, monkeys, and gorillas. These nonhuman wild primates are omnivores. They are also often described as herbivores and opportunistic carnivores in that although they eat mainly fruits and vegetables, they may also eat small animals, lizards, and eggs if given the opportunity. For example, the gorilla and the orangutan eat only 1 percent and 2 percent of animal foods as a percentage of total calories, respectively. The remainder of their diet is derived from plant foods. Since humans are between the weight of the gorilla and orangutan, it has been suggested that humans are designed to eat around 1.5 percent of their diet in the form of animal foods. However, most Americans derive well over 50 percent of their calories from animal foods.
Since wild primates fill up on wild fruit and other highly nutritious plant foods, those weighing one tenth the amount of a typical human ingest nearly ten times the level of vitamin C and much higher amounts of many other vitamins and minerals (see Table 1.1). How is this possible? One reason is that the cultivated fruit in an American supermarket is far different from the wild fruit of the primate's diet, having a slightly higher protein content and a higher content of certain essential vitamins and minerals. Cultivated fruit tends to be higher in sugars and, while very tasty to humans, it is not nearly as nutritious. In fact, it raises blood sugar levels much more quickly than its wild counterparts do.
There are other differences in the wild primate diet that are also important to highlight, such as a higher ratio of alpha-linolenic acid -- the essential omega-3 fatty acid -- to linoleic acid -- the essential omega-6 fatty acid. A higher ratio of omega-3 fatty acid decreases the likelihood of the development of inflammatory and chronic diseases as well as their severity. Finally, the wild primate diet is very high in fiber, while the average American diet is not. A high-fiber diet protects against heart disease and many types of cancer.
Determining what diet humans are best suited for may not be as simple as looking at the diet of wild primates. Humans have some significant structural and physiological differences compared to apes. The key difference may be our larger, more metabolically active brains. In fact, it has been theorized that a shift in dietary intake to more animal foods may have produced the stimulus for human brain growth. The shift itself was probably the result of limited food availability, which forced early humans to hunt grazing mammals such as antelope and gazelle. Archaeological data support this association -- humans' brains started to grow and become more developed at about the same time evidence shows an increase of animal bones being butchered with stone tools at early villages.
While improved dietary quality alone cannot fully explain why human brains grew, it definitely appears to have played a critical role. With their bigger brains, early humans were able to engage in more complex social behavior, which led to improved foraging and hunting tactics, which, in turn, led to even higher quality food intake that fostered additional brain evolution.
Data from anthropologists looking at evidence from hunter-gatherer cultures is providing much insight as to what humans are designed to eat. However, it is important to point out that these cultures were not entirely free to determine their diets. Instead, their diets were molded as a result of what was available to them. For example, the diet of the Inuit Eskimos is far different from that of the Australian Aborigines. Therefore, it may not be appropriate to answer the question "What should humans eat?" simply by looking at these studies alone.
Nonetheless, regardless of whether a hunter-gatherer community relied on animal or plant foods, the rate of diseases of civilization such as heart disease and cancers was extremely low.
How is this possible? One reason is that the meat our ancestors consumed was much different from the meat we find in the supermarket today. Domesticated animals have always had higher fat levels than their wild counterparts, but the desire for tender meat has driven the fat content of domesticated animals to 25 to 30 percent or higher compared to a fat content of less than 4 percent for free-living animals or wild game. In addition, the type of fat is considerably different. Domestic beef contains primarily saturated fats and virtually undetectable amounts of omega-3 fatty acids. In contrast, the fat of wild animals contains over five times more polyunsaturated fat per gram and has desirable amounts of beneficial omega-3 fatty acids (approximately 4 percent).
What conclusions can we draw from the evidence of the wild primate and hunter-gatherer diets about how we should eat today? Overwhelmingly, it appears that humans are better suited to a diet composed primarily of plant foods. This position is supported also by a tremendous amount of evidence showing that deviating from a predominantly plant-based diet is a major factor in the development of heart disease, cancer, strokes, arthritis, and many other chronic degenerative diseases. It is now the recommendation of many health and medical organizations that the human diet should focus primarily on plant-based foods, comprising vegetables, fruits, grains, legumes, nuts, and seeds.
The evidence supporting diet's role in chronic degenerative diseases is substantial. There are two basic facts linking the diet-disease connection:
1. A diet rich in plant foods is protective against many diseases that are extremely common in Western society.
2. A diet providing a low intake of plant foods is a causative factor in the development of these diseases and provides conditions under which other causative factors became more active.
The Pioneering Work of Denis Burkitt and Hugh Trowell
Much of the link between diet and chronic disease originated from the work of two medical pioneers: Denis Burkitt, M.D., and Hugh Trowell, M.D., editors of Western Diseases: Their Emergence and Prevention, first published in 1981. Although now extremely well recognized, the work of Burkitt and Trowell is actually a continuation of the landmark work of Weston A. Price, a dentist and author of Nutrition and Physical Degeneration. In the early 1900s, Dr. Price traveled the world observing changes in teeth and palate (orthodontic) structure as various cultures discarded traditional dietary practices in favor of a more "civilized" diet. Price was able to follow individuals as well as cultures over periods of twenty to forty years, and he carefully documented the onset of degenerative diseases as their diets changed.
Based on the extensive studies examining the rate of diseases in various populations (epidemiological data), including the groundbreaking work of Dr. Price and their own observations of primitive cultures, Burkitt and Trowell formulated the following sequence of events:
First stage: In cultures consuming a traditional diet consisting of whole, unprocessed foods, the rate of chronic diseases, such as heart disease, diabetes, and cancer is quite low.
Second stage: Commencing with eating a more "Western" diet, there is a sharp rise in the number of individuals with obesity and diabetes.
Third stage: As more and more people abandon their traditional diet, conditions that were once quite rare become extremely common.
Examples of these conditions include constipation, hemorrhoids, varicose veins, and appendicitis.
Fourth stage: Finally, with full Westernization of the diet, other chronic degenerative or potentially lethal diseases, including heart disease, cancer, osteoarthritis, rheumatoid arthritis, and gout, become extremely common.
Since the publication in Western Diseases of Burkitt and Trowell's pioneering research, a virtual landslide of data has continually verified the role of the Western diet as the key factor in virtually every chronic disease, but especially in obesity and diabetes. In 1984, the Food and Nutrition Board of the National Research Council established the Committee on Diet and Health to undertake a comprehensive analysis on diet and major chronic diseases. Their findings, as well as those of the U.S. surgeon general, the National Cancer Institute, and other highly respected medical groups brought to the forefront the need for Americans to change their eating habits to reduce their risk for chronic disease. Table 1.2 lists diseases with convincing links to a diet low in plant foods. Many of these now-common diseases were extremely rare before the twentieth century.
Trends in U.S. Food Consumption
During the twentieth century, food consumption patterns changed dramatically. Total dietary fat intake increased from 32 percent of calories in 1909 to 43 percent by the end of the century; carbohydrate intake dropped from 57 percent to 46 percent; and protein intake has remained fairly stable at about 11 percent.
Compounding these detrimental changes are the individual food choices accounting for the changes. There were significant increases in the consumption of meat, fats and oils, and sugars and sweeteners in conjunction with a decreased consumption of noncitrus fruits, vegetables, and whole-grain products. But the biggest change in the last hundred years of human nutrition was the switch from a diet with a high level of complex carbohydrates, as found naturally occurring in grains and vegetables, to a tremendous and dramatic increase in the number of calories consumed in the form of simple sugars. Currently, more than half of the carbohydrates being consumed are in the form of sugars such as sucrose (table sugar) and corn syrup, which are added to foods as sweetening agents. High consumption of refined sugars is linked to many chronic diseases, including obesity, diabetes, heart disease, and cancer.
The Government and Nutrition Education
Throughout the years, various governmental organizations have published dietary guidelines, but it has been the recommendations of the U.S. Department of Agriculture (USDA) that have become the most widely known. In 1956, the USDA published "Food for Fitness -- A Daily Food Guide." This became popularly known as the Basic Four Food Groups. The Basic Four were:
1. The Milk Group: milk, cheese, ice cream, and other milk-based foods
2. The Meat Group: meat, fish, poultry, and eggs, with dried legumes and nuts as alternatives
3. The Fruits and Vegetables Group
4. The Breads and Cereals Group
One of the major problems with the Basic Four Food Groups model was that it suggested graphically that the food groups were equal in health value. The result was an overconsumption of animal products, dietary fat, and refined carbohydrates and insufficient consumption of fiber-rich foods such as fruits, vegetables, and legumes. This in turn resulted in the diet being responsible for many premature deaths, chronic diseases, and increased health care costs.
To replace the Basic Four Food Groups model, various other government and medical organizations developed guidelines of their own, designed either to reduce a specific chronic degenerative disease such as cancer or heart disease or to reduce the risk for all chronic diseases.
In an attempt to create a new model in nutrition education, the USDA published the "Eating Right Pyramid" in 1992. Since it received harsh criticism from numerous experts and other organizations, it was altered visually in 2005 (see page 10).
One of the main criticisms of the Eating Right Pyramid is that it does not stress strongly enough the importance of quality food choices. For example, the USDA thinks foods from the Bread, Cereal, Rice, & Pasta Group should make up the bulk of your diet. Eat six to eleven servings a day from this group, and you are supposedly on your way to a healthier life. What the pyramid doesn't tell you is that you are setting yourself up for insulin resistance, obesity, and adult-onset diabetes if you consistently choose refined products (those containing white flour) rather than whole-grain products in this important category.
You see, the Eating Right Pyramid does not take into consideration how quickly blood sugar levels rise after eating a particular type of food -- an effect referred to as the food's glycemic index, or GI. The GI is a numerical scale used to indicate how fast and how high a particular food raises blood glucose (blood sugar) levels. There are two versions of the GI, one based on a standard of comparison that uses glucose scored as 100, while the other is based on white bread. Foods are tested against the results of the selected standard. Foods with a lower glycemic index create a slower rise in blood sugar, while foods with a higher glycemic index create a faster rise in blood sugar.
The glycemic indices of some of the foods the pyramid is directing Americans to eat more of, such as breads, cereals, rice, and pasta, can greatly stress blood sugar control, especially if they are derived from refined grains, and are now being linked to an increased risk for obesity, diabetes, and cancer. As a result, while the goal of the Eating Right Pyramid was to improve the health of Americans and, it was hoped, slow down the growing trend for obesity and diet-related disease, the fact is that because of poor individual food choices within the categories, the pyramid has only worsened the problem.
In light of this, the big question consumers may want to ask is "Is it appropriate to have the USDA making these food recommendations in the first place?" After all, the USDA serves two somewhat conflicting roles. First, it represents the food industry, and second, it is in charge of educating consumers about nutrition. Many people believe that the pyramid was more weighted toward dairy products, red meat, and grains due to the influence of the dairy, beef, and grain farming and processing industries. In other words, the pyramid was not designed as a way to improve the health of Americans but rather to promote the USDA agenda of supporting multinational food giants.
The Optimal Health Food Pyramid
We do like the concept of graphically illustrating what constitutes a healthful diet, so we are offering our version of the Eating Right Pyramid: the Optimal Health Food Pyramid.
The Optimal Health Food Pyramid incorporates the best aspects from two of the most healthful diets ever studied: the traditional Mediterranean diet and the traditional Asian diet. It also more clearly defines what the healthy components within the categories are and stresses the importance of regular consumption of vegetable oils as part of a healthy diet. Let's take a closer look at each category.
Foods to avoid entirely:
Vegetables: Five to Seven Servings Daily
The word "vegetable" comes from the Latin vegetare, meaning "to enliven or animate." Vegetables give us life and should be the main focus of any health-promoting diet. Vegetables provide the broadest range of nutrients of any food class. They are rich sources of vitamins, minerals, carbohydrates, and protein. They also provide high quantities of cancer-fighting phytochemicals.
It is very important not to overcook vegetables. Overcooking will not only result in the loss of important nutrients, it will also drain the flavor. Light steaming, baking, and quick stir-frying are the best ways to cook vegetables. And do not boil vegetables unless you are making soup, as much of the nutrients will leach into the water.
If fresh vegetables are not available, frozen vegetables are preferred over their canned counterparts. The only exception is tomato products, for example, soup, paste, or sauce, because canned products actually provide more absorbable lycopene than do raw tomatoes.
There are three vegetable categories: green leafy and cruciferous; low-glycemic; and starchy. Eating a variety of vegetables from each category daily will help you achieve a "rainbow" assortment and allow you to focus on low-glycemic choices.
Good Oils and Fats (Nuts, Seeds, and Vegetable Oils): Four Servings Daily
Nuts and seeds, especially those providing the monounsaturated and medium-chain fatty acids, contain beneficial oils. Regular consumption of nuts has been shown to improve blood sugar regulation and lower the risk for diabetes, heart disease, obesity, and cancer.
Be sure to focus on raw nuts and seeds, avoiding nuts and seeds roasted in oils or coated with sugar. Nuts and seeds are great to add to salads and sauteed greens. Try to mix it up a bit by eating a variety such as almonds, Brazil nuts, flaxseeds, pecans, pumpkin seeds, sunflower seeds, walnuts, and pumpkin seeds.
Use canola, flaxseed, macadamia, or olive oil to replace the butter, margarine, and shortening that you use for cooking, or try them in your homemade salad dressings. However, you never want to cook with flaxseed oil because it is very rich in omega-3 polyunsaturated fats, which are easily damaged by heat. Coconut and macadamia nut oils are the best cooking oils because of their ability to remain stable at high temperatures, but olive oil is great for sauteed vegetables and canola oil is usually best for baked goods because it has the least "nutty" flavor. Avoid using safflower, sunflower, soy, and corn oil because they contain too much omega-6 fatty acid, which feeds into inflammatory pathways in the body.
We suggest that you have at least one serving of nuts or seeds (one serving equals 1/4 cup) and 3 tablespoons of the healthy oils per day.
Whole Grains: Three to Five Servings Daily
It is very important to choose whole-grain products, such as whole-grain breads, whole-grain flour products, and brown rice, over their processed counterparts, including white bread, white flour products, and white rice. Whole grains provide substantially more nutrients and health-promoting properties. They are a major source of complex carbohydrates, dietary fiber, magnesium and other minerals, and B vitamins. The protein content and quality of whole grains is also greater than that of refined grains. Diets rich in whole grains have been shown to be helpful in both the prevention and treatment of diabetes, heart disease, and cancer.
One serving of whole grains equals:
Whole-wheat, rye, or 1 slice other whole grain
Whole-grain cereal 1/2 cup
Cooked whole-kernel 1/2 cup corn
Corn on cob 1 small
Flour and flour products:
Whole-wheat flour 21/2 tablespoons (unbaked)
Whole-grain pasta 1/2 cup (cooked)
Amaranth, barley, 1/2 cup millet, oats, quinoa, rice, spelt, and wheat
Two to Three Servings Daily
Beans, a mainstay in most diets of the world, are second only to grains in supplying calories and protein to the world's population. Compared to grains, they supply about the same number of total calories but usually provide two to four times as much protein and are a richer source of the soluble fiber that lowers cholesterol and stabilizes blood sugar levels. While we do not recommend using canned vegetables or fruit, canned beans retain their fiber content and anticancer flavonoids. Plus, given the long preparation time for cooking beans, canned beans are extremely quick and convenient. A serving size for beans is 1/2 cup.
Fruits: Three to Four Servings Daily
Fruits are a rich source of many beneficial nutrients, and regular fruit consumption has been shown to offer significant protection against chronic degenerative diseases, including cancer, heart disease, cataracts, diabetes, and stroke. Fruits make excellent between-meals snacks and super desserts. We know it's easy to get into the habit of eating only a few varieties of fruit, so we encourage you to eat a "rainbow" assortment of fruits over the course of a week. Keep in mind that one serving equals one 1 medium fruit or 1/2 cup of small or cut-up fruit; 4 ounces of 100 percent juice; or 1/4 cup dried fruit.
Two to Three Servings Daily
The detrimental effects of diets high in saturated fat and cholesterol have been stressed for decades. Likewise, the importance of the omega-3 fatty acids in the battle against chronic disease is now well known. Fish consumption, in particular, has shown tremendous protection against heart disease and cancer because of the high content of omega-3 fatty acids in fish. Choosing smaller species of fatty fish, such as wild salmon, mackerel, herring, and sardines, is best because their smaller size and shorter life span translate into a smaller accumulation of mercury, PCBs, and other environmental toxins. Wild-caught fish have less accumulation than farmed fish. Because of concerns about exposure to mercury and other environmental toxins, we recommend that you consume wild fish at least three, but no more than six, times per week.
We suggest that you limit your intake of red meat (beef, veal, or lamb) to no more than two servings per month and choose the leanest cuts possible. Do not charbroil or cook the meat until well done, as this increases the formation of cancer-causing compounds. Also, consider some of the alternatives to beef, such as venison, buffalo, elk, rabbit, and ostrich. These emerging beef alternatives are lower in saturated fat and provide higher levels of omega-3 fatty acids.
Chicken and turkey can also provide excellent protein with very little fat, especially if you eat only the white meat (breast) and do not eat the skin. Eggs are also a very good source of high-quality protein and, if produced by free-range hens fed flaxseed meal, are rich in beneficial omega-3 fatty acids.
One serving is about the size of a deck of cards. That translates to roughly 3 to 4 ounces.
Dairy: One to Two Servings Daily (Optional)
Many people are allergic to milk or lack the enzymes necessary to digest dairy products. Even for people who do tolerate dairy foods, milk consumption should be limited to no more than one or two servings per day. Although dairy foods are rich in protein and calcium, they are also high in fat and calories, lacking the wide nutrient spectrum of foods in the categories previously discussed. Dairy foods can also contain accumulations of agricultural chemicals and hormones if not organically produced. Use organic, nonfat, or reduced-fat dairy products over whole-milk varieties whenever possible. Also, fermented dairy products such as yogurt, kefir, and acidophilus-fortified milk are preferred over milk due to their content of beneficial bacteria, which predigest the dairy proteins and sugars. If you haven't tried some of the soy milk alternatives to cow's milk, they are delicious, especially the flavored varieties, which include vanilla and chocolate.
One serving equals 1 cup of milk, yogurt, or cottage cheese or 1 ounce of cheese. If you do not consume dairy products, we recommend that you take a calcium supplement.
The Optimal Health Food Pyramid and the dietary guidelines given reflect the current scientific answer to the ideal diet for most people. They are based upon a 2,000-calorie-a-day diet. If you need to increase your caloric intake, we recommend getting the extra calories you need by increasing the number of servings of vegetables, nuts, and legumes, as these are the best foods for improving blood sugar control. Athletes or people engaged in heavy physical labor or exercise should add another serving of seafood, meat, or poultry to their daily intake or add a soy protein or whey protein smoothie to provide an additional 25 to 30 grams of protein.
The following chapters explain the recommendations of the Optimal Health Food Pyramid in depth and more clearly define the benefits, features, and importance of consuming healing foods.
Copyright © 2005 by Michael Murray, N.D., Joseph Pizzorno, N.D., and Lara Pizzorno