Eating for your genes

What makes some people crave coffee so much more than others? There is mounting evidence that we are genetically predisposed to prefer certain foods—which may explain why an individual, say, loves mashed potatoes but hates turnips. Another study by El-Sohemy looked at the gene GLUT2. People with a particular form of it consume more sugar on a daily basis than others. It seems that this version of the gene may prevent individuals from recognizing changes in their blood sugar levels—and signalling to the brain when to stop eating. Building on this, El-Sohemy is now researching why some people have a strong aversion to foods such as broccoli, even though their parents enjoy it. These broccoli haters, it appears, have inherited two copies of a gene that makes them overly sensitive to bitter taste.

Now-famous research on the herb cilantro also shows that some people may be genetically predisposed to dislike specific foods. Studies by Charles J. Wysocki at the Monell Chemical Senses Center in Philadelphia revealed that the most common complaint about cilantro is that it tastes soapy; fans describe it as fresh and citrusy. Wysocki suspects that people who dislike the herb may be missing a genetic component that would help them detect the chemicals that make it pleasant for others. He’s also found that identical twins (who share the same DNA) feel the same about cilantro, unlike fraternal twins.

This deluge of research on the genetic basis for dietary preferences and their impact on people is exactly as it sounds: exciting, overwhelming and scattered. There is still much more that’s unknown. Each finding raises questions about whether the results will be true for both genders, different ethnicities, and depending on each individual’s medical status. The Stanford study, for instance, included mostly Caucasian women. Interleukin’s Bender acknowledges the limitations of the company’s genetic test for diets. “Clearly we want to do further work with the existing test,” he says, “and create better versions going forward.”

To develop the test, Interleukin sifted through hundreds of genes associated with obesity that have been identified over the years. They whittled those down to 16 genes that had been studied in multiple, independent, large-scale clinical trials. Those were then downsized to five genes whose “biological function” (their code, and role in the body) are known. The Interleukin team referred to the Obesity Gene Map, a compendium of literature pioneered by Louise Pérusse at Université Laval, though he has no association with the company. “We have more evidence that genetics can affect the way we respond to diet,” Pérusse says. “On that principle it makes sense to identify a gene and find out what could be your best diet.” But Pérusse says there is one caveat: “The field is still evolving,” he warns, “So the question is, are these the best genes” to test for?

What’s more, experts say that genetics is only one part of the reason why some people struggle with weight. Gardner says environmental factors have an even bigger impact. While conducting the Stanford study, one woman had the full support of her spouse, but another was sabotaged by hers. One participant’s daughter died. He believes social support and emotional distress factors have an influence on a person’s success at losing weight. He’s heartened by the current food movement that has seen farmers’ markets flourish, and ignited debate about local and sustainable food. “If you go to the school or work cafeteria and all they serve is crap then it doesn’t matter if you know your genotype if all your food choices are poor.”

Like others studying nutrigenomics, Gardner is wary of foiled dieters thinking that “eating for your genes” will be the magic bullet—one that negates the need to cut out junk food or exercise. One woman who watched the Oz show wrote to Gardner pleading for advice. She had failed to lose weight using every diet on the market. “I wrote back, ‘If there are 10 diets available and you tried all 10, this isn’t going to make one of the 10 work now,’ ” says Gardner. “It must mean she’s got other issues. It’s not a perfect solution. It’s not, ‘Oh thank God, the obesity epidemic is over.’ ” Not yet, anyway.

EVEN BIGGER

The Canadian Health Measures Survey compared the physical characteristics and fitness levels of individuals in 1981 to the period between 2007 and 2009. Below, how the average 45-year-old man and woman has changed with time—and it’s not for the better in many ways.

SOURCE: Shields M, Tremblay MS, Laviolette M, Craig CL, Janssen I, Connor Gorber S. Fitness of Canadian adults: results from the 2007-2009 Canadian Health Measures Survey.
Health Reports 2010; 21: 1-15.

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