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Ask a Medcan registered dietitian: Is there value to a DNA-driven diet?

Nutrigenomics may help explain a debated link between caffeine and heart health

DNA molecule on a plate

The name is a mouthful, but nutrigenomics is essentially the study of how our genes interact with the foods we eat.  It looks at how our genetic makeup influences how we digest, absorb and metabolize foods.

Nutrigenomics research also seeks to understand how nutrients in our diet affect gene expression, the process by which proteins are made in cells. Proteins such as hormones, enzymes, and cell receptors then go on to perform important functions in the body.  How our diet and genes interact can make us healthier or increase our risk for disease.

Have you ever wondered why some people lose weight easily following certain diet but others don’t even though they’re eating the exact same diet? Or why some people are more likely than others to gain weight on a high fat diet?  The fact that people respond differently to different diets can be explained, at least in part, by nutrigenomics.

In the almost two decades since researchers sequenced the human genome, the cost and speed of genetic testing has dropped significantly.   You’ve probably seen advertisements for genetic tests that claim to tell you which foods are best for you – and which ones aren’t – to stay healthy, lose weight, and so on.

Is the science behind nutrition and genetics the real deal?  Let the research guide you

I’m often asked that question in a variety of ways. In other words, are we able to customize diets based on your genetic makeup?  Advances in technology have allowed nutrigenomics research to expand very quickly. And while study findings connecting diet, genes and health are very exciting, the research is still evolving.

One tantalizing study published in 2012 suggests that people who carry a variation of an obesity-associated gene called FTO will lose more weight and body fat on a high protein diet than they will on a low protein diet (1). This finding was exciting because it suggested that we may be able to personalize weight-loss diets. However, the study was a relatively small one. And other studies have found no effect of the FTO gene on weight loss.

A cardiologist’s perspective on caffeine and genetic screening

Nutrigenomics may help to explain conflicting results from studies on caffeine intake and risk of cardiovascular disease.  A gene called CYP1A2 controls for an enzyme that breaks down caffeine in the body; variations of this gene affect the speed at which people clear caffeine from their body. Your risk of heart attack appears to be related, in part, to whether you are a “slow” or “fast” caffeine metabolizer (3). Fast metabolizers appear to have no greater risk of heart attack, even if their caffeine consumption exceeds the equivalent of four cups of coffee per day.  In contrast, slow metabolizers may have an increased risk even drinking as few as two cups of coffee a day.

Dr. Chi-Ming Chow, a cardiologist at Medcan, offers more perspective.

“Caffeine is the most widely used drug in the world. Since its use is so widespread it can be hard to assess the effect of the drug in isolation,” says Dr. Chow. “Caffeine is a naturally occurring stimulant found in coffee, tea, chocolate, and used as an additive in other beverages and adjuvant analgesic in some pain medications. It has long been known that genetic variation influences caffeine responses, indeed caffeine has been used as a probe drug for phenotyping CYP1A2 activity”.

“Although there may be some beneficial effects of caffeine or coffee intake for particular individuals in the prevention of diseases, for others caffeine use may be associated with increased risk of disease, drug interactions, adverse events, and harm. Current studies have failed to validate clear relationships between gene variants, caffeine intake, and phenotypes. Work is needed to better define the functional variants that are involved in caffeine response. In addition, the components of coffee in addition to caffeine should be considered as these may have confounding effects in their actions on AHR and CYP1A2.”

Using caffeine for athletic performance? Consider this

If you’re runner or cyclist, take note: although caffeine is widely thought to improve endurance performance, a recent study out of the University of Toronto suggests that may be true only if you’re a fast caffeine metabolizer (4).  Slow metabolizers who were given caffeine during a 10-km cycle time trial, showed no increase in performance or performed worse than when they cycled without caffeine. “Athletes who use caffeine to improve their performance don’t necessarily know if caffeine is helping them or hindering them because they do so by trial-and-error” said study author Ahmed El-Sohemy.

Ultimately, the usefulness of nutrigenomic test results depends largely on the strength of the evidence behind the gene variation being tested. That’s why it’s important that such testing be conducted and interpreted by a trained healthcare provider, such as a registered dietitian.

“I cannot stress enough the importance of context when it comes to genetic testing. Having a dietitian or other healthcare provider interpret nutrigenomic results in the context of your bloodwork, activity levels and health history is where the true value lies,” says Allison Hazell, Clinical Director of Genetics at Medcan.

Like family history and standard blood testing, knowing your personal genetic profile is useful, but it is only one of many important data points in determining health risk.

Alex Friel is a registered dietitian at Medcan, an eternal student and an avid runner. You can contact her at or book an appointment by phone (416) 350-3621 or by email


  1. Zhang X et al. FTO Genotype and 2-Year Change in Body Composition and Fat Distribution in Response to Weight-Loss Diets. 2012;61(11):3005-3011
  2. Cornelis et al. Coffee, CYPA1 genotype, and risk of myocardial infarction. Journal of the American Medical Association. 2006;2951135-1141.
  3. Guest N, Corey P, Vescovi JEl-Sohemy A. Caffeine, CYP1A2 Genotype, and Endurance Performance in Athletes. Medicine and Science in Sports and Exercise. doi: 10.1249/MSS.0000000000001596. [Epub ahead of print]

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