ZUMA/KEYSTONE
Few physicians have the cachet or the captive audience of Dr. Mehmet Oz. He’s written half a dozen books, and has been on the The Oprah Winfrey Show no less than 55 times. She nicknamed him “America’s doctor,” and every weekday he hosts his own radio and television talk shows. So, last month, when a segment of Dr. Oz was devoted to “exploring the perfect diet for your genes,” the nascent field of “nutrigenomics” was catapulted into pop science stardom.
“It’s totally sexy,” says Christopher Gardner, a Stanford University researcher who co-authored the study featured on Dr. Oz, which had not yet been published in a peer-reviewed journal as of late April. The study suggests that a simple genetic test (a mouth swab) may pinpoint for individuals exactly what kind of diet they should be on—low-fat, low-carb or balanced—to drop the maximum number of pounds. “Lots of people know they should go on a diet. Lots of people are pissed because they went on the same diet that their friend went on and their friend lost more weight than they did,” muses Gardner, who is also a professor at Stanford’s medical school. Hopefully, this study, he says, “will explain part of that.”
Understanding the relationship between our DNA, dietary preferences and the impact that food has on us is at the core of nutrigenomics. “We study how our individual genetic differences—the variations and the sequence of a particular gene—can explain why some people respond differently than others,” says Ahmed El-Sohemy, the Canada Research Chair in Nutrigenomics, and a professor at the University of Toronto. “Ultimately, the goal is to develop better, personalized dietary advice for the individual. Because we know that the one-size-fits-all model is not the most effective.”
One thing does apply to practically everybody: 95 per cent of people who lose weight on a diet will gain it back within a few years; 41 per cent will get even heavier, according to Oz. Last year, a Nielsen survey found that 44 per cent of Canadians said they were trying to lose weight, mainly by cutting down on fat. At the same time, the Canadian Health Measures Survey showed that the average 45-year-old male is now 20 lb. heavier and has gained seven centimetres around his waist compared to his counterpart in 1981. Given these discouraging statistics, it’s no wonder that the “eat for your genes” ethos has been embraced. Soon after Oz’s show, the Massachusetts company that developed and sells the genetic test used in the Stanford study was inundated with calls from media, doctors and consumers. “There’s been a significant spike in sales,” says Interleukin Genetics CEO Lew Bender. “And it’s continuing.”
Gardner, who says he wasn’t paid by Interleukin, is reluctant to discuss the study until it’s accepted by a journal; he turned down an invitation to be on the Oz show (though his comments were used when preliminary findings were presented at an American Heart Association conference in March). But according to Bender, the study reveals that of the 138 women who were genetically tested, those on a diet matched to their genotype lost about 13 lb., compared to just two pounds among mismatched participants. There were improvements in metabolic factors such as cholesterol, triglyceride levels and waist circumference. As far as Bender is concerned, this study proves that the key to losing weight is reducing the right type of calories from your diet—fat, carbohydrates or protein, known as macronutrients—depending on your genes.
Macronutrients are the building blocks of our daily diet. Today, health authorities recommend that roughly half of the calories an adult consumes in one day come from carbohydrates, a third from fat, and the rest from protein. But as more genes are identified and understood in relation to obesity, it is becoming clear that not everyone processes food in the same way—so one individual may need more or less of a given macronutrient than another person.
Caffeine is a perfect example. A study led by El-Sohemy identified two types of a gene that differently affect how quickly a person processes caffeine. Those individuals with the slow version of the gene who drank two or three cups of coffee a day had a 36 per cent greater chance of heart attack—and four or more cups of coffee upped the risk to 64 per cent. People with the fast version of the gene had a 22 per cent lower risk of heart attack.
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