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Are You Really What You Eat?
Scientists are discovering more about the relationship among genes, diet, and health. By John Pekkanen
Comments () | Published April 1, 2010
John Milner of the National Cancer Institute believes nutrigenomic research could lead to “nutritional preemption” of some forms of cancer and other chronic illnesses. Photograph by Chris Leaman.

Editor's note: Genetic tests are about to become much more accessible: Walgreen's has announced that it will begin selling genetic test kits at its 7,500 drugstores across the country. This article, from the April Washingtonian, focuses on how genetic tests might be used to lose weight and improve your health.  

 

Dr. Melik: This morning for breakfast he requested something called wheat germ, organic honey, and tiger’s milk.

Dr. Aragon: Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties.

Dr. Melik: You mean there was no deep fat? No steak or cream pies or hot fudge?

Dr. Aragon: Those were thought to be unhealthy—precisely the opposite of what we now know to be true.

—From the 1973 Woody Allen comedy “Sleeper.” The doctors are discussing the eating habits of Allen’s character, who awakens in the 22nd century after a slumber of 200 years.

If you’ve wondered whether the green tea you’re drinking is really good for you or whether having a glass of red wine will help you live longer—as it seems to do for the French—or whether passing up a juicy steak for a plate of steamed vegetables will keep you healthier, answers are on the way. But they may not be the ones you expect.

An emerging science called nutritional genomics is illuminating how the food we eat influences our genes and our health.

This new knowledge won’t be as fanciful as Sleeper, but in time it will revolutionize our understanding of the relationship between diet and health. We’ll learn why certain foods might be lifesaving for some but, because of genetic variations, might bring no benefit—or could even be harmful—to others.

We’re seeing a similar phenomenon with therapeutic drugs. A drug that may save one person’s life might jeopardize another’s and for a third have no effect. This is why genetic testing has emerged as an important part of cancer treatment, guiding physicians’ selections of drugs to treat individual patients.

Similarly, nutritional genomics—or nutrigenomics, as it’s also known—will let us individualize healthy dietary choices in ways that go well beyond what we can learn from family history. Scientific evidence suggests that dietary habits are related to a third of all cancers, and diet plays a powerful role in cardiovascular disease, obesity, diabetes, and other chronic infirmities.

Individualized genetic tests already exist to help predict the most effective diet for losing weight and delaying or preventing some forms of cardiovascular disease, and more tests are emerging. But consumers beware: Some commercial labs market genetic tests over the Internet purporting to guide dietary choices, but experts say they offer incomplete and often worthless information.

“The power of nutritional genomics is enormous,” says Ruth DeBusk, a geneticist and dietician and the author of Genetics: The Nutrition Connection, “because it will allow us to prevent disease, especially chronic disease, by manipulating our diet. But the big challenge right now is not to oversell it before the science is ready.”

Nutritional genomics will alter but not completely overturn conventional dietary advice.

“There will always be population-based recommendations for diet to address the basic needs of biology,” says Sharon Ross, program director of the Nutritional Science Research Group in the Division of Cancer Prevention at the National Cancer Institute in Bethesda. “But nutritional genomics could give us the ability to make recommendations to clusters of individuals who have genetic differences that might require them to consume more or less of a specific nutrient to reduce their risk of disease.”

Although the field of nutrigenomics is new, its antecedents reach back to the 1960s, when the first newborn screening programs for phenylketonuria—or PKU—were mandated in all 50 states. PKU is a genetic metabolic disorder in which the body can’t break down an amino acid called phenylalanine. Untreated, PKU can lead to mental retardation, but a low-phenylalanine diet can prevent it. The PKU experience demonstrated that the interplay between nutrients and genes can be powerful.

“The work with PKU makes it clear that the way we handle food is different for different people,” says Artemis P. Simopoulos, past president of the International Society of Nutrigenetics/Nutrigenomics and formerly an NIH researcher and director of the newborn nursery at George Washington University Hospital. “If you took ten people and gave them four eggs a day, five of them would not show any change in their cholesterol, but the other five would—and that’s because of their genetic makeup. We also know that 50 percent of heart attacks for men under 50 occur in only 5 percent of families. Nutritional genomics not only will help identify who is at risk but also will help establish nutritional guidelines.”

Consider the “lower your fat intake” mantra for people with high cholesterol levels.

“We know of a subgroup of society who have what is called a Type 4 hyperlipoproteinemia,” says John Milner, chief of the Nutritional Science Research Group in the National Cancer Institute’s Division of Cancer Prevention. “They have elevated cholesterol, and Type 4 means it is carbohydrate-induced. They account for about 15 percent of the population. The classic recommendation we have today for people with elevated cholesterol is to lower fat intake, and when people lower fat intake, they usually increase their intake of carbohydrates such as vegetables and grains. When this doesn’t work, they’re given a statin drug to lower their cholesterol. But for that 15 percent, switching to more carbohydrates and less fat actually increases their cholesterol level, so with these people we are making an error—they don’t need the drug, and they don’t need to lower their fat intake.”

Milner says that a test for this genetic variation would make it possible to identify people with this form of high cholesterol in order to prevent them from taking unneeded medication and eating the wrong diet.

It’s widely known that moderate alcohol consumption can help lower the risk of heart disease for many, but less well known is that perhaps 20 percent of people have a variation on a gene called Apo E that reverses the protective effect of alcohol.

Similar variations are seen with regard to cancer. Milner says some people have a genetic variant that makes them “highly susceptible” to colorectal cancer if they eat meat regularly, especially red meat. For most of these people, substituting fish for meat will reduce this risk. But Milner adds that because of genetic variations, a high-fish diet may increase disease risk for some.

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