Picture this: One day in the future you go to a clinic for healthy eating. You open wide and a nurse takes a swab from the inside of your cheek. That sample is whisked off to a lab, where your DNA is tested. A few weeks later you get a report, recommending a diet specifically geared to make you healthier.

You’ve got to really boost your leafy greens and fortified cereals, it says. Your body doesn’t process folic acid as well as others so you need up to three times as much in your diet. It also doesn’t deal with fat well, and you’ve got to watch the cream, butter and fudge. The report explains why you gain weight during the holidays; you’ve got a gene that makes you more likely to munch when stressed.

Your spouse has a rosier picture. The test reveals a genetic variant that can metabolize caffeine quickly, and allows a coffee habit without harmful cardiac consequences. But, refined carbohydrates could become a problem because a gene that metabolizes those seems to be deficient. No more white bread, pasta and cupcakes.

That kind of personalization is the promise of nutrigenomics, an emerging science that describes how food interacts with our DNA. It aims to move dietary advice beyond the general – low-fat diets are good – to the specific by describing how variations among different people’s genes make them react to food differently. It is beginning to deepen our knowledge of how our diets affect our health. Ultimately, it may change the way we think about eating.

“We have to move from the general recommendation to the more personalized science-based recommendation,” says Jose Ordovas, a professor of nutrition and genetics at Tufts University and national expert on nutrigenomics. “Sometime in the future,” he says, “we’ll say your genes are in such a way that you don’t need to have a low-fat diet, as long as you maintain the proper caloric intake.”

Nutrigenomics is part of the trend in health care toward increasingly targeted treatments, with everything from cancer therapy to prescription medications becoming more tailored toward a unique patient’s needs. Enabled by our burgeoning knowledge of the human genome, scientists can now look more closely at our differences than ever before, down to the level of a single gene on a single chromosome. That gives them the ability to precisely describe how drugs or nutrients affect the human body. More powerfully, it also enables a prediction about what treatments or diets will work for which individuals and why those things will work.

“We’ve known for many years that some people eat whatever they want and don’t get obese, and some people can’t,” says Ordovas. “Nutrigenomics will make us able to identify and tell us how to fix the problem.”

You are what you eat

Many people are familiar with the concept that variations in each person’s DNA are what make each of us unique. Because your genes are slightly different from the person sitting next to you, you have straight hair or curly, green eyes or brown, long legs or short.

But genes also determine how our bodies respond to the food we eat. Eat a salad, for example, and your body will digest it and break it down into its various parts, including the nutrients folic acid, vitamin K and vitamin C. Depending on your particular configuration of DNA, you may absorb more or less of those nutrients than other people. Ordovas likens it to the gas pedal on a car. If the gas pedal is not sensitive, then when you push it, you will need to apply more pressure to get the same speed. Similarly, if a person’s gene is not as sensitive as another’s, the former may need more nutrients to get the same result.

Ordovas uses the example of a low-fat diet. In many people, the amount of fat they eat affects the amount of cholesterol in their body. Some people, however, seem to be immune to its effect, maintaining healthy cholesterol no matter their diet. As Ordovas says, “their genes compensate for the excess of fat.”

Scientists are just now beginning to learn which genes do what to affect the way our body processes food. Once they know more, they will be able to give people recommendations more closely tailored toward their genetic type. That could end the era in which we have general recommendations for good health. Eat your veggies could give way to eat the best veggies for you.

“It helps us to understand what kind of recommendations we should be giving,” says Ahmed El-Sohemy, a professor of nutritional sciences at the University of Toronto and the Canada Research Chair of Nutrigenomics. “Eat less, exercise more; that’s prudent advice for everyone. But in terms of shifting, we might say you should cut back on refined carbohydrates because your body doesn’t respond to it.”

Eventually, nutrigenomics will enable better predictions about how foods will affect someone. Today’s diets are recommended through educated guesses, says Eris Craven, a nutritionist at Bend Memorial Clinic. “Most of it is trial and error. You look at (the person) and you put together a prescription and give it a few weeks and kind of wait and see.”

With nutrigenomics, a person’s genetic profile could become a guide to the diet that will work best for that individual and, perhaps what foods will cause a negative reaction. Though Craven says she does not use nutrigenomics heavily now, she thinks she will in the future. “That’s where nutrition is going.”

However, scientists emphasize that the processes that govern how nutrients affect our blood pressure, cholesterol levels and other aspects of health are complex, and no one yet knows the number of genes involves. “We have found several of those genes,” says Ordovas, “but not all.”

World of possibilities

Those several genes, however, are tantalizing enough to both consumers and companies that a fair number of nutrigenomic products are already on the market. Many test a handful of genes and recommend certain diets, or their own supplements, based on the results.

For example, Salugen, a San-Diego-based company, markets a variety of tests to consumers, spas and physicians that measure deficiencies in some genes. The company uses genetic information to postulate the reasons behind various health issues from weight gain to addiction. “There’s a certain a-ha experience in knowing this is the culprit and this is what I can do about it,” says Salugen CEO Brian Meshkin.

The company’s consumer product, GenoTrim, uses a cheek swab to test five genes that the company dubs “the sweet tooth gene,” “the fat regulator gene,” “the nervous eating gene,” “the new cell gene” and “the obesity risk gene.” Meshkin admits that the five genes do not give the whole picture of what is causing obesity, for example, but he says testing all related genes would be much more expensive and that having any information leads to a better decision.

Based on the variants in each of those genes, the test reports to each person whether he or she is at risk for a variety of both behavioral or medical problems, including obesity, insulin sensitivity, depression, even compulsive gambling. Then, the customer can buy a customized weight-management supplement that will help get a handle on those issues that could have been obstacles in the past.

“It’s not a magic pill,” says Tom Cross, the owner of the Eugene franchise of DNA Services of America, a genetic counseling firm that sells GenoTrim. “But we’re in addition to a program that someone might be on.”

However, some scientists say that companies that recommend diets or sell supplements based on genetic profiles are not scientifically sound, because the science isn’t there yet. “When we have such a powerful tool, like genomics, there’s obviously great interest in trying to capitalize on that and make it available to the public, but most academics would say that you have to tread carefully,” says El-Sohemy.

“This is still very preliminary,” says Ordovas. “We have over 20,000 genes and many of them are involved in the major problems that occupy the mind of people: heart disease, obesity, cancer. Any of these companies are only looking at one, two, 19 genes.”

A federal report chastised companies that used nutrigenetics (sometimes used synonymously with nutrigenomics) to sell tests and supplements. The report, published in July 2006 by the Government Accountability Office, found that the nutrigenetic tests “misled consumers by making predictions that are medically unproven and so ambiguous that they do not provide meaningful information to consumers.” The GAO found that the tests did not provide unique genetic profiles, and that they recommended “personalized” vitamins for about $1,200 per year that are similar to a supplement that could be bought at a grocery store for $35 per year.

And though the report itself was not well received – El-Sohemy says it was “done terribly” – its point was well-taken in the scientific community: The promise is exciting, but today’s reality may not yet live up to those expectations.

You vs. me

With all its futuristic promises, some of the concepts around personalized nutrition and medicine are not new. In about 400 B.C., Hippocrates referenced individual differences in people’s ability to cope with disease. In eastern medicine, people are categorized by body type and given ways to avoid ailments common to each type.

More recently, we’ve become used to giving our family history to our doctors as a way to assess what we might fall victim to ourselves. Doctors use family histories as a crude measure of genetic susceptibility. If Dad and Grandpa died of a heart attack, you better get your own heart checked.

And, there are a multitude of tests that give an idea of differences or suggest recommendations to better your own health. At BMC, Craven says she uses a person’s cholesterol level, body fat percentage, waist circumference, glucose level and blood pressure, among other things, to build a personalized diet for a patient. Still, as nutrigenomics comes into its own, Craven says, it could improve all of our eating habits. “When your genes are the support, who can argue?”

What is nutrigenomics?

Nutrigenomics is an emerging science that describes how nutrients in food interact with our genes. A cousin of pharmacogenomics, which examines how pharmaceutical drugs react with genes, nutrigenomics promises to personalize dietary advice and could change the way we think about healthy eating.