In the quest for your ideal diet, take clues from your ancestors and members of your family.
IN THE PAST two decades, nutrition has become a subject of great popular interest. Advertisements and labels proclaim what various foods do and do not contain. Books and articles abound on diets that can lower everything from our weight to our risk of various illnesses. We speak in casual conversation about our cholesterol and triglyceride levels and have learned the differences between saturated, unsaturated and hydrogenated fats.
All this attention we pay to nutrition is based on the premise that what we eat affords us some measure of control over our health and that proper nutrition is a one-size-fits-all proposition with little relationship to our personal genetic background makeup. But is it?
A recent book by naturopathic physician Peter D'Adamo, N.D., Eat Right 4 Your Type (Putnam, 1996), made waves with a bold theory about how our individual genetic makeup affects what each of us should and should not eat. To maintain optimal health, D'Adamo argues that specific blood types-A, B, AB and Oshould dictate our diets.
One of D'Adamo's assertions is that people with type O blood (about 46 percent of the population) should be eating meat virtually every day in order to remain healthy. According to D'Adamo, type O's are direct descendants of those who roamed the earth before the advent of agriculture, and therefore, have "huntergatherer" genes, which dictate a preagricultural diet-one free of cultivated products, such as oats, wheat and most other grains. By contrast, those with blood types that originated after the start of agriculture can eat these foods. Persons with type A blood, he claims, are best off as vegetarians, while type B's are basically omnivores and the only ones who do well eating dairy products. People whose blood type is AB have the nutritional needs and intolerances of types A and B.
D'Adamo's book has been roundly criticized by a variety of experts. "There is no anthropological evidence whatsoever that all prehistoric people with a particular blood type ate the same diet," says Stephen Bailey, Ph.D., a nutritional anthropologist at Tufts University in Medford, Mass. The Tufts University Health and Nutrition Letter bluntly called D'Adamo's book "a blood bad idea."
"It's the latest diet fad. It's not backed up by good science," states Bonnie Liebman, director of nutrition at the Center for Science in the Public Interest in Washington, D.C. "I think people who are talking about these individualized diets are just trying to sell books. I guarantee that the blood-type theory will be gone within a year."
NOBODY DISPUTES the fact that our genes play a major role in determining our health, and that, consequently, there are things we must do to safeguard it. But four genetic attributes alone cannot account for the vast complex that is the human body nor for any one person's multiple needs. Human DNA the double helix molecule in each cell that is its genetic blueprint-is made up of 50,000 to 100,000 genes, not just four types, and these genes are shuffled and reshuffled each generation, creating an incredible variety of traits, tendencies and requirements particular to each individual.
Genes lay the groundwork for who a person is and how he fares, but they alone do not determine the finished product. "Almost always it's not just a single gene that causes a disease, for instance," says Liebman. "It's an interaction between environment and a gene that causes disease." And one of the major elements of the human environment is diet.
In fact, the foods that have been available over the millennia have had a profound effect on who survived to pass along their genes to subsequent generations. For example, during times of food scarcity, individuals who were genetically predisposed to store fat were more likely to survive than individuals without this tendency. Scientists speculate that this capacity may explain why obesity and related illnesses are so prevalent today-prehistoric peoples who were able to store fat lived through lean times and passed along that characteristic to their descendants.
Similarly, scientists hypothesize that the reason people from central and northwestern Europe and some parts of Africa are able to digest lactose, while many adults in most of the rest of the world are lactose-intolerant, is that these areas have a long history of dairy farming. According to the report Diet and Health: Implications for Reducing Chronic Disease Risk by the Committee on Diet and Health, a research arm of the National Research Council (National Academy Press, 1989), the gene for lactase persistence [ability to digest lactose] conveyed a survival advantage to people in dairy farming cultures in which milk products were a primary source of nutrients. Over the generations, this gene proliferated in the population because people who were able to absorb milk as children and young adults were either more fertile or less likely to die early.
Clearly, our genes have a major role in determining the nature of our responses to the foods we eat and, in turn, our health. So the question raised by D'Adamo's book and other recent books that have promoted highly individualized diets is this: How can each of us figure out the diet that will be best for our unique genetic selves? The answer lies in a true understanding of our genetic heritage, both ancient and modern.
Even though we may be only a few decades old, our genes are ancient. They have been passed along, in various combinations, from person to person since prehistoric times. And while we may pride ourselves on being adaptable, the same can not be said for our genes. They evolved to fit into a long-ago world we can now barely recognize. In essence, we inhabit a contemporary universe with primitive genes that have not been able to respond rapidly enough to the pace of change affecting our surroundings.
THE HUMAN GENETIC constitution has changed relatively little since the appearance of truly modern human beings, Homo sapiens, about 40,000 years ago," says S. Boyd Eaton, M.D., a professor in the School of Medicine and the Department of Anthropology at Emory University in Atlanta. "Even the development of agriculture 10,000 years ago has apparently had a minimal influence on our genes." In other words, our genes still assume that we are hunter-gatherers, eating a diet that varies according to location and season. They presume we spend our days in constant motion, hunting and foraging for our food.
When stable agricultural societies appeared, they radically altered what people ate and how much time they spent on the move, collecting food, but our genes remained what they had always been since it takes many millennia for genes to adapt to new circumstances.
Agriculture not only introduced and emphasized new foods but modified mankind's nutritional intake. Domesticated animals yielded meat much higher in saturated fats than did wild animals. Cultivated grains didn't provide the rich source of omega-3 fatty acids found in wild greens. And then, with the development of modem growing-and-processing technology, foods were exposed to fertilizers, pesticides and environmental toxins, stripped of fiber and nutrients, and pumped full of fillers and additives our ancestors never encountered.
As a result, we now eat a diet we were not designed for and experience illnesses unknown to our ancestors. "Human beings today are confronted with diet-related health problems for which prior genetic adaptation has poorly prepared them," Eaton says.
EVOLUTION AND DIET
THIs FACT has led many researchers to try to shape a modern diet based on the ancient model. Such books as Eaton's The Paleolithic Prescription (HarperCollins, 1989) suggest ways in which we could return to a diet more in line with our evolutionary development.
The evidence on which diets such as Eaton's are based comes primarily from archeological digs that uncover relics of our past. The earliest human fossil is from Australopithecus, who lived more than 2 million years ago. Australopithecus walked upright and ate mainly fruits and nuts. About 2 million years ago came Homo habilus, who used tools and scavenged for food, followed by Homo erectus who emerged about 1.7 million years ago, and hunted and used fire. "Eating meat became systematic with erectus," says Alan Walker, Ph.D., of Johns Hopkins University in Baltimore, Md.
Despite this evolution in dietary habits, there's no reason to believe that during any one prehistoric period all members of the species were eating the same things. They ate what was available, and that depended on where they lived. Still, anthropologists make some generalizations based on the fossil evidence, including the fact that meat has been a part of the human diet for at least 1.7 million years.
But, like current efforts to craft highly individualized diets based on blood type, the efforts to devise modern versions of prehistoric diets failed to adequately allow for the incredible nutritional flexibility of the human body and the vast differences between foods available then and now. Our ancestors were omnivores, capable of living on a wide variety of foods but dependent on none. They were able to derive their protein from any number of sources, plant and animal, and passed along those omnivorous genes to us. When meat was available, they ate it. When it wasn't, they were fine without it. D'Adamo's claims aside, there was no one pattern of eating to which all hunter-gatherers adhered.
Clearly, our ancient ancestors didn't have the luxury of choosing not to eat meat. A general scarcity of food required them to eat whatever they could get, whenever they could get it. That's what it means to be an omnivore-not having a reason to eat everything, but having the capacity to do so successfully. And this ability is what we have inherited-what all of us, regardless of our individual genetic makeup, have inherited.
TODAY, WE have an entire public health industry advising us on nutritional principles. Yet, there is a remarkable level of consensus among its major players, which include the National Institutes of Health, the National Cancer Institute and the American Dietetic Association. All these organizations recommend a grain-based diet that derives less than 30 percent of calories from fat (no more than one third of these from saturated fat) and includes less than 2,400 milligrams of sodium, at least 5 daily servings of fruits and vegetables and at least 25 grams of dietary fiber.
Still, there is no question that individuals can have nutritional needs that diverge quite dramatically from the norm. A good example of how general nutritional advice recognizes individual requirements is the complicated calculations that go into determining (and periodically updating) the U.S. Recommended Dietary Allowances (RDAs). On the surface, the specific numbers of calories, grams of fat, international units of vitamin A, milligrams of calcium and so on seem to reflect an intimate knowledge of what each of us needs. These numbers are based on the realization that every person is genetically unique and, in fact, are carefully calculated averages that take into account the fact that each individual processes the same food differently; the recommendations accommodate vast variations in the absorption, digestion, usage, storage and excretion of various nutrients. But the RDAs are only a starting point.
They are designed to satisfy the needs of 90 percent of the population, specifying too much of a given nutrient for 5 percent and too little for 5 percent. And even for the 90 percent for whom the averages are accurate, they are only a dietary launching pad. Anyone with a predisposition to a specific illness will need much larger quantities of certain nutrients, as will anyone with a metabolic disorder that causes them to either absorb too much or too little of a particular nutrient.
So while the general advice about nutrition applies pretty well to most of us, our individual genetic makeup does affect how healthy we will be if we don't tailor that advice to our own genetically influenced needs. And much of the information about our individual genetic makeup can be gleaned from an analysis of our more recent genetic past-our family.
THE FAMILY CONNECTION
IF YOUR GRANDMOTHER fell and broke her hip, you may have a tendency toward osteoporosis and would be wise to pay more attention to your calcium intake. If your grandfather died of a heart attack and your father had a bypass operation, you are probably well-advised to reduce your consumption of saturated fats and increase the amount of antioxidants you ingest.
Similarly, some families are more prone than others to colon cancer, high blood pressure, various allergies, obesity, alcoholism and diabetes. These conditions provide valuable clues to your genetic legacy and suggest how to customize your food regimens to fit your genetically shaped requirements. These afflictions, especially, call for the grain-based diet endorsed by the public health industry.
Of course, it's difficult to ferret out how much of a family pattern of illness is genetically determined. In addition to genes, family members tend to share eating, drinking and stress stimuli as well as exercise and smoking habits. Still, recent research has unearthed genetic predispositions to many illnesses, putting people in families that are prone to those ailments on notice to be extra cautious. "Not everyone is at the same degree of risk for disease," says Artemis Simopoulos, M.D., president of the Center for Genetics, Nutrition and Health and co-author of Genetic Nutrition: Designing a Diet Based on Your Family Medical History (Macmillan, 1993). "Each one of us is unique, but we are more similar to our brothers and sisters and our parents than we are to the rest of the world."
So where does this leave us? How do we integrate what we know about our genetic history, both ancient and recent, with generalizations about healthful diets proffered by agencies that make recommendations for the public health?
The best advice seems to be to regard the general suggestions as a benchmark and then customize your own diet according to what you know about your family's health history, your own health indicators (such as cholesterol and triglyceride levels) and the way you feel.
Public nutrition advice will always be firmly entrenched in the language of generalizations. To muster your best chances for good health, you need to personalize that advice, factoring in your own genetic legacy. You may choose to consult with a dietitian or nutritionist who shares your overall perspective of health, but whatever methods you employ to shape your diet, keep in mind that a healthful one depends on a high level of activism.
Ed Blonz, Ph.D., is a nutrition consultant, researcher and author of YOUR PERSONAL NUTRITIONIST series published by Signet. Winner of the 1996 James Beard Foundation award for his story in VEGETARIAN TIMES on deciphering scientific studies, Blonz lives in Kensington, Calif.…