Some experts believe you can use diet to influence how your
body responds to your genetic makeup.
By Lisa James
Height, eye color, wavy or straight hair: Such attributes are determined in large part by your genes.
Genes are responsible for more than your appearance, however. Your body cannot carry out the biological processes that keep you alive without instructions from all your genes—your genome—acting in concert. Genomics, the study of the genome, has spawned a number of related fields. One is nutrigenomics—the study of how nutrients and genes interact.
Experts say that the capacity for relatively low-cost genomic testing is right around the corner. Some in the field say the age of personalized nutrition has dawned—that each person can be given a diet and lifestyle plan for optimal health based on his or her genomic information. Other authorities believe it’s too early to make that claim, that the technology has not yet been fully developed. All agree that nutrition and genetics interact in ways that we are only beginning to understand.
Genes and Nutrients
The nutrients you include—or neglect—in your diet can affect how your genes are expressed. Eating a low-antioxidant diet has been found to cause genetic changes linked to asthma development (OMICS 10/09). In one study, men who ate a diet rich in refined grains and saturated fat were at risk of developing type 2 diabetes, but only if they were genetically susceptible to the disease (American Journal of Clinical Nutrition 5/09).
Scientists have learned that some gene variants, or alleles, increase the risk of developing certain diseases. Apolipoprotein E (APOE) is a key factor in cholesterol metabolism. The gene that carries the APOE code occurs in three main forms, two of which have been linked to high cholesterol, atherosclerosis and Alzheimer’s disease. Testing can reveal the presence of problematic forms of APOE; a combination of high-risk APOE and a high-fat diet results in a greater chance of developing metabolic syndrome, a risk factor for cardiovascular disease (Atherosclerosis 1/3/10 online).
Obesity is an example of how environmental influences can play havoc with one’s genetic heritage. “Some of us were born with ‘thrifty’ genetics, genes whose function is to hold onto every extra calorie and store it as fat,” says Peter D’Adamo, ND, director of the New England Center for Personalized Medicine in Wilton, Connecticut and author of Change Your Genetic Destiny (Broadway Books). When food is scarce, such genes are helpful. But when faced with an overload of refined carbs, these genes “hog their places at the microphone,” as D’Adamo puts it, drowning out other genes and causing weight to rise. More than 250 genes have been implicated in obesity—a number researchers expect to keep growing (Obesity 12/08).
Part of the link between genetics and nutrition may lie in how different people’s bodies are able to adapt, or not, to a lack of specific nutrients. “Vitamin D is a perfect example. In some people there’s a gene that only acts abnormally if there are low vitamin D levels, increasing the person’s risk of multiple sclerosis. If there are normal vitamin D levels, the person’s gene acts fine,” says Brandon Colby, MD, author of Outsmart Your Genes (Perigee/Penguin).
D’Adamo adds, “Turns out your mom was right—a daily multiple might help in ways that we’re only just now coming to appreciate fully.”
From Lab to Clinic
As studies continue, some practitioners are bringing genomic information from the lab into the clinic. “While we may have the code, the translation from DNA to everything that encompasses the genome into practical health realities is still in the early stages of being elaborated,” says D’Adamo. “But what we do know is feeding into medical research that is already bearing fruit.”
One factor driving the clinical use of genomics is its rapidly falling cost. Last year scientists at Stanford University were able to completely sequence one person’s genome for $50,000. But it is estimated that the cost of such sequencing may fall to $1,000, or less, within the next several years.
Even $1,000 might be more than many people would be willing to pay out of pocket for a full genome scan. “To get to the point where we have genetic-based dietary guidelines, third-party payers would have to cover that,” says Catherine McCarty, PhD, MPH, senior research scientist at the Center for Human Genetics, Marshfield Clinic Research Foundation in Marshfield, Wisconsin.
More readily available is genetic testing via panels, or tests grouped together by function—panels that test for women’s disorders or for cardiovascular disease, for example. “Panels are extremely powerful tools because they enable simultaneous genetic screening for all the diseases and traits that are targeted to a specific need,” says Colby.
D’Adamo takes a different approach. He believes that people fall into one of six “GenoTypes,” basic responses to environmental and genetic factors. For instance, the hunter adapted to the harsh circumstances of early human existence through an immune system that reacted strongly to outside threats. This gives hunters a distinct advantage in fighting harmful micro-organisms. However, “their hair-trigger immune response can sometimes lead to over-reaction in the form of allergies, asthma and other inflammatory conditions,” says D’Adamo. His approach is to help each patient adapt to the shortcomings of whatever GenoType he or she falls into. In the case of hunters, who have trouble digesting grains, that means a diet which emphasizes beef and lamb while avoiding wheat and a lifestyle that includes plenty of regular, vigorous exercise.
In a sense, genetic testing is a sophisticated extension of the medical history questionnaires issued routinely to new patients. “Your family tree shows the people in your family who are at risk for certain illnesses. And it sounds the warnings years in advance,” says Chris Reading, MD, author of Trace Your Genes to Health (Vital Health). If the practitioner is rushed for time and doesn’t read the document carefully, however, the advantage of taking a medical history is lost.
In the same way, the results of genetic testing require interpretation. That, experts say, is where the real challenge begins.
Practitioners of what Colby calls “predictive medicine” generally take a dim view of direct-to-consumer (DTC) genetic testing, in which patients deal with testing laboratories themselves. Colby says a report produced by a DTC lab “is nothing more than a high-tech paperweight” unless a professional interprets the data.
For example, genetic testing on one of the patients in Colby’s Los Angeles practice revealed vulnerabilities to prostate cancer and to high levels of homocysteine, an amino acid linked to heart disease. As a result, Colby put the patient on a diet high in lycopene for prostate protection and in B vitamins to help control homocysteine.
Geneticists are concerned about the effects of DTC testing. A Federal Drug Administration advisory panel is studying what it calls “the risks and benefits” of making genetic tests directly available to the public.
Where many lab scientists part ways with predictive medicine practitioners is on whether personalized nutrition, in which diets can be tailored to each person’s genetic needs, is a workable idea today. “We’re not there yet,” says McCarty. “The tools needed to evaluate this data are developing.”
Another problem is that people may not properly evaluate risk. “We should not confuse increased and decreased risk with absolute certainties. The classic example is smoking and lung cancer; we all know of nonsmokers who get lung cancer. Nothing is an absolute,” says Nicholas Katsanis, PhD, director of the Center for Human Disease Modeling at the Institute of Genetic Medicine, Duke University School of Medicine.
Katsanis is also concerned that the rush to practice may affect the nature of genetic research. He says, “We don’t know what questions we haven’t asked yet. We should not ignore anything that will allow us to make a paradigm shift.”
Both Katsanis and McCarty point out that knowledge of your genome isn’t necessary to practice basic, sensible self-care. Katsanis notes that a number of mutations have been linked to diabetes risk. But so is having a large waist, he says. “That’s best addressed through diet and exercise,” he adds, “no matter what your genetic mutations are.”