A trip to the diet doc, circa 2013. You prick your finger, draw a little blood and send it, along with a $100 fee, to a consumer genomics lab in California. There, it’s passed through a mass spectrometer, where its proteins are analyzed. It is cross-referenced with your DNA profile. A few days later, you get an e-mail message with your recommended diet for the next four weeks. It doesn’t look too bad: lots of salmon, spinach, selenium supplements, bread with olive oil. Unsure of just how lucky you ought to feel, you call up a few friends to see what their diets look like. There are plenty of quirks. A Greek co-worker is getting clams, crab, liver and tofu — a bounty of B vitamins to raise her coenzyme levels. A friend in Chicago, a second-generation Zambian, has been prescribed popcorn, kale, peaches in their own juice and club soda. (This looks a lot like the hypertension-reducing ”Dash” diet, which doesn’t work for everyone but apparently works for him.) He is allowed some chicken, prepared in a saltless marinade, hold the open flame — and he gets extra vitamin D because there’s not enough sunshine for him at his latitude. (His brother’s diet, interestingly enough, is a fair bit different.) Your boss, who seems to have won some sort of genetic lottery, gets to eat plenty of peanut butter, red meat and boutique cheeses.

Nobody is eating exactly what you are. Your diet is uniquely tailored. It is determined by the specific demands of your genetic signature, and it perfectly balances your micronutrient and macronutrient needs. Sick days have become a foggy memory. (Foggy memory itself is now treated with extracts of ginkgo biloba and a cocktail of omega-3 fatty acids.)

”Ultimately, the feedback you’ll get will be continuous,” says Wasyl Malyj, an ”informatics” scientist at the University of California at Davis working with the new Center of Excellence for Nutritional Genomics, who is helping me blue-sky here. The appeal of this kind of laser-targeted diet intervention is hard to miss. If you turn out to be among the population whose cholesterol count doesn’t react much to diet, you’ll be able to go ahead and eat those bacon sandwiches. You’ll no longer be spending money on vitamin supplements that aren’t doing anything for you; you’ll take only the vitamins you need, in precisely the right doses. And there’s a real chance of extending your life — by postponing the onset of diseases to which you’re naturally susceptible — without having to buy even a single book by Deepak Chopra.

This, then, is the promise — and the hype — of nutritional genomics, the second wave of personalized medicine to come rolling out of the Human Genome Project (after pharmacogenomics, or designer drugs). The premise is simple: diet is a big factor in chronic disease, responsible, some say, for a third of most types of cancer. Dietary chemicals change the expression of one’s genes and even the genome itself. And — here’s the key — the influence of diet on health depends on an individual’s genetic makeup.

How does that work? Consider what happens, biologically, when we eat a meal. Until quite recently, most scientists thought food had basically one job: it was metabolized to provide energy for the cell. Indeed, that is what happens to most dietary chemicals — but not all of them. Some of them don’t get metabolized at all; instead, the moment they’re ingested, they peel off and become ligands, molecules that bind to proteins involved in ”turning on” certain genes to one degree or another. A diet that’s particularly out of balance, nutritional-genomics scientists say, will cause gene expressions that nudge us toward chronic illness — unless a precisely tailored ”intelligent diet” is employed to restore the equilibrium.

Take genestein, a chemical in soy, which attaches to estrogen receptors and starts regulating genes. Different individuals may have estrogen receptors that react to genestein differently. Genetic variations like that one, some scientists say, help explain why two people can eat exactly the same diet and respond very differently to it — one maintaining his weight, for example, and the other ballooning.

There is a buzz around nutritional genomics at the moment, which is partly a matter of timing. A sea change is under way in the approach scientists are taking to disease — they’re looking less to nature or nurture alone for answers, and more to the interactive symphony of ”systems biology” that nutrigenomics epitomizes.

At the same time, chatter around this new science has been amplified by a controversy. The idea of the biological relevance of race — even its very existence — is hotly debated. And the assumption of real genetic markers that distinguish one ethnic group from another is at the philosophical heart of nutrigenomics.

Here’s the most familiar example: If you’re of Northern European ancestry, you can probably digest milk, and if you’re Southeast Asian, you probably can’t. In most mammals, the gene for lactose tolerance switches off once an animal matures beyond the weaning years. Humans shared that fate as well — until a mutation in the DNA of an isolated population of Northern Europeans around 10,000 years ago introduced an adaptive tolerance for nutrient-rich milk. The likelihood that you tolerate milk depends on the degree to which you have Northern European blood.

”That, essentially, is the model — a very dramatic one,” says Jim Kaput, the founder of NutraGenomics, a biotechnology company. ”As humans evolved, and as our bodies interacted with foods on each of the continents, we sort of self-selected for these naturally occurring variants. And certain populations have variants that, when presented with Western-type food — which is usually fatty and overprocessed and high in calories — pushes them toward disease rather than health.”

Plenty of examples bear out this ill fit between certain cultures and certain diets — suggesting, if not quite proving, some interplay of genes and nutrition: the Japanese who relocated to the United States after World War II soon saw their cholesterol levels soar. The Alaskan Inuit, whose metabolism was perfectly suited to moving around all day, looking for high-fat food, were suddenly saddled with an evolutionary disadvantage when they began living in heated homes and traveling on snowmobiles, and they now show high levels of obesity, diabetes and cardiovascular disease. The Masai of East Africa have developed new health problems since they abandoned their traditional cattle-meat-and-blood-and-milk diet for corn and beans.

The cradle of nutrigenomics is the cradle of humankind itself: the original migration out of Africa created widely separated subpopulations with distinct collections of gene variants. The members of each subpopulation tend to respond similarly to diet and environmental conditions. But the genetics of race is an inexact science. And since many people have ancestors from different continents — making them a genetic admixture — the data are rarely clean-cut. In other words, ethnicity is relevant to nutritional genomics, but only as a starting point. Which is why the idea of sorting ourselves by race and pursuing a diet consistent with the original continental diet isn’t going to be very helpful. And why, in fact, the customized diets of most people’s perfect genomic future will probably not be all that different from one another.

Kaput estimates that the middle 60 percent of the bell curve are probably not going to need to deviate too much from the basic fruit-and-vegetable-heavy diet recommended by the Department of Agriculture. The folks who will benefit from customized nutritional packets, he says, will be the 20 percent at either end: those at the top who don’t have to worry much about what they eat — and will thus be able to cut corners — and the 20 percent on the bottom, who respond disastrously to conventional diets and will discover that they need to follow special diets or eat specific supplements. The problem for everyone will be figuring out where they fall on the curve of each disease profile.

Just how far in the future are we projecting here? When will nutrigenomics be ready for public consumption? Even many of those who have faith in the science concede that the staggering complexity of interactions among genes, and between genes and the environment, will be a real challenge to solve. As a workable concept, ”eat right for your genotype” may be a decade or two — or more — down the road.

”Right now, no one in their right mind would offer genetic testing or tell you what drug to take,” says Dr. Muin Khoury, director of the Office of Genomics and Disease Prevention at the Centers for Disease Control. Despite that warning, a handful of companies are already offering genomics profiles and nutritional supplements to early adopters looking for an edge. One company, the North Carolina-based Great Smokies Diagnostic Laboratory, offers a genetics-testing service called Genovations. Clients pay up to $1,500 for a preventive health profile.

For nutrigenomics to realize its potential, though, vast, ethnically diverse databases of genomic profiles will have to be assembled, from which researchers will try to divine patterns.

But that, of course, opens up a whole new can of genetically modified worms. Once our genotypes are in databanks, can we really be sure they won’t be sold to employers or insurance companies? And in what social gulag will those poor saps find themselves who simply cannot resist tucking into a double-cheese all-beef sub during the seventh-inning stretch?

Some people can eat slabs of steak and butter without gaining weight or raising their cholesterol levels. Others assiduously shun fats and still have a high risk of heart disease. The different response to diet is determined in part by one’s genes.

Now scientists are beginning to apply genetics to diet, a new field known as nutritional genomics, or nutrigenomics. In the near term, the study is expected to reveal how particular diet ingredients affect health. The ultimate goal will be to tailor one’s diet to genetic makeup.

Mass market products like corn flakes may one day come in different varieties, geared to different subsets of people based on their genes. And dietary guidelines issued by the government or medical societies will have to make more distinctions based on genetic profiles.

”We’re moving into an era where the one-size-fits-all public health strategy for disease prevention will not apply as it currently does,” said Dr. Muin J. Khoury, director of the Office of Genomics and Disease Prevention at the Centers for Disease Control and Prevention.

Pharmaceutical companies are working on a related field known as pharmacogenomics, with the goal of developing so-called personalized medicine. It is known that people with certain genetic variations will not receive benefit from certain painkillers or will suffer serious side effects from a dose of a cancer drug that helps others.

Nutrigenomics would expand the idea of personalized care into the consumer world. ”This will take the benefit of the Human Genome Project and extend it from the hospital to the home,” said Dr. Raymond L. Rodriguez, a professor of molecular and cellular biology at the University of California at Davis.

Already there are some examples. People with phenylketonuria, a rare inherited disease that leads to mental retardation, can avert problems with a special diet low in proteins. People with a particular gene variant cannot digest milk.

The advent of consumer genetics is also raising concerns. Already some small companies are offering vitamins or dietary advice customized to people based on genetic tests. Customers swab the inside of their cheeks with cotton to obtain their DNA.

But many experts say not enough is known yet to support the claims of these companies. ”I’m really skeptical that this is going to lead to health benefits at the stage of knowledge we’re in,” said Dr. Ronald M. Krauss, a senior scientist at the Lawrence Berkeley National Laboratory who was the chairman of the dietary guidelines committee of the American Heart Association.

The companies defend their tests. ”This is not voodoo; this is science,” said John R. DePhillipo, chief executive of GeneLink, of Margate, N.J., which is developing customized vitamins and skin products based on gene tests. NuGenix, a company owned by Mr. DePhillipo’s children, recently began selling customized vitamins at $300 for the test and a one-month supply.

GeneLink does not make public which genes it tests for, but one of them is manganese superoxide dismutase, which is involved in reducing so-called oxidative stress. A variant of the gene that is not as efficient as other forms has been shown to raise the risk of breast cancer, Parkinson’s disease and other diseases, said Dr. Robert P. Ricciardi, a professor of microbiology at the University of Pennsylvania and a founder of GeneLink.

People with this variant would be given vitamins with an extra dose of antioxidants. ”It’s giving some sort of rational approach to nutrients and formulations,” said Dr. Ricciardi. ”A lot of people are just mega-dosing on stuff.”

Sciona, a British company, is selling customized dietary advice for about $200. The company tests for 19 variations in nine genes. Six genes are involved in removing toxins from the bodies. Consumers who have variations that the company says slow this process are advised, for instance, to avoid well-done red meats, which have higher levels of certain toxins.

Another test is for the gene that produces Mthfr, an enzyme involved in using folic acid, an important vitamin. People with a less efficient version of this gene are told to eat more liver, broccoli and other foods rich in the vitamin.

Outside experts acknowledge that scientific papers link certain diseases to genetic variations and diet. But they say dozens or hundreds of genes may be involved. In some cases, data on genetic variations can be conflicting. In addition, they say, the companies have not proved that the diet or vitamins they recommend will really make a difference. For instance, Dr. Khoury of the C.D.C. said, it is not clear that people with the Mthfr variant need more folic acid than they are already getting.

”There is so much uncertainty about the meaning of these genetic tests,” he said. ”Right now we are telling people to exercise, eat well, eat a diet high in fiber, low in fat. From what I see, so far there is no added clinical benefit from the genetic tests.”

Dr. Helen Wallace, deputy director of GeneWatch U.K., a group that led opposition to Sciona’s test, said the advice was too generalized to be worth paying for. ”Most of us could probably do with eating more broccoli,” she said.

Dr. Chris Martin, Sciona’s chief executive, said that although some of the advice was common sense, people took it ”much more seriously” because it was personalized. He said the company had sold more than 600 tests so far.

Genetic tests that are offered as services, in contrast to those offered as testing kits, are not stringently regulated by the Food and Drug Administration. Companies do not have to prove claims, for example, that a particular genetic variation is linked to a higher risk of disease or the inability to use a vitamin. And dietary supplements and cosmetics are also lightly regulated.

Another concern is that some genes that may be tested for dietary purposes are risk factors for serious diseases. Should consumers be told, and do they risk being denied insurance or jobs if that information leaks out? Do they need medical advice? Sciona initially sold its advice through retail stores, but after controversy arose, it is now selling only through doctors and dietitians.

People with a version of a gene called APOE, for instance, tend to have their cholesterol go up or down more rapidly in response to dietary changes, Dr. Krauss said. But this same gene variant, known as APOE4, also means a higher risk of Alzheimer’s disease. ”We don’t even like to measure APOE anymore because it would get people worried about Alzheimer’s,” he said. In some cases, he and others said, it is not necessary to test genes. Other tests, like those for cholesterol, can help guide diet decisions.

Still, despite skepticism about some early applications, interest is growing. Several companies, some still operating in their founders’ living rooms, have sprung up: Galileo Laboratories in Santa Clara, Calif.; Alphagenics of Gaithersburg, Md.; NutraGenomics of Chicago; and NuDisCo of St. Louis.

Bigger food and consumer products companies like Unilever, Nestlé and Kraft are at least monitoring the field. Interleukin Genetics, a company that studies variations of genes involved in inflammation, announced last month that it was in talks with a ”major consumer products company” about developing nutritional supplements and skin care products based on genetic information.

But much of the early focus is not on customizing foods but on using genomics to unravel the mechanisms by which certain food ingredients affect the body. ”We’d like to know the molecular mechanism of nutrients,” said Dr. Young S. Kim, a program director at the National Cancer Institute, which recently held a workshop on nutritional genomics and cancer prevention.

Scientists at Johns Hopkins have found which genes are turned on by sulforaphane, a compound in broccoli that helps prevent cancer. Dr. Len Augenlicht, professor of medicine and cell biology at the Albert Einstein Cancer Center in the Bronx, found that different genes were turned on and off in mice when they ate the rodent equivalent of an unhealthy Western diet than when they ate a healthy diet.

Dr. Jose M. Ordovas, director of nutrition and genomics at the Agriculture Department’s Human Nutrition Research Center at Tufts, said dietary guidelines would soon have to be customized. ”There are some people at very high risk of cardiovascular disease who, if they follow the current recommendations, they make it even worse,” he said.

Moderate alcohol consumption, he said, is considered to reduce risk of heart disease. But for people with the Alzheimers-linked APOE4 gene, alcohol consumption raises the level of bad cholesterol. People with a certain variant of a gene called APOA1 should eat more polyunsaturated fats than called for in the guidelines.

Nutrigenomics could raise questions about policies to fortify foods. If it is found that only a subset of the population benefits from fortified foods, ”do you give a whole population a higher exposure than normal to a nutrient, without knowing what the risk is?” asked Dr. Patrick J. Stover, the director of the Cornell Institute for Nutritional Genomics.

DNA News Resource:  http://www.nytimes.com/2002/10/01/health/new-era-of-consumer-genetics-raises-hope-and-concerns.html

DNA Nutritional Breakthrough:  http://www.dnaguidedwellnessproducts.com