Gene cuisine - genetics and diet

Vegetarian Times, Oct, 1997 by Ed Blonz

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?

BLOOD-TYPE HYPE

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 O--should 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 "hunter-gatherer" 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."

GENETICS COUNT

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.