What's The Science Behind Personalized Diets Based On Your DNA? : The Salt There's an explosion of interest in personalized diet approaches and at-home test kits are popping up everywhere. Part of the approach includes analyzing your DNA, but genes can only tell us so much.

Personalized Diets: Can Your Genes Really Tell You What To Eat?

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All right. So genetic tests can help you explore your heritage, but can your DNA also tell you what diet is best for you? NPR's Allison Aubrey asked that question.

ALLISON AUBREY, BYLINE: If you're curious about personalized nutrition advice, meet Kimberly Desjardine. She was, too. So a few months ago, she paid a couple hundred dollars for a personalized nutrition service called Habit. Now, to get the process started, she used an at-home test kit. She swabbed the inside of her cheek to get a DNA sample, and she pricked her finger to get blood samples. She then mailed them to a lab for evaluation, and here's what she learned.

KIMBERLY DESJARDINE: I think the aha's that came out of the test were that I was a protein seeker. It just basically said that I need more protein than the average person.

AUBREY: The recommendation was partially based on the results of her blood test. It showed her response to starch and sugar was not good. So high-protein foods, she was told, would be better. The test also showed that she had a variant of a gene that makes her sensitive to caffeine.

DESJARDINE: Information like that makes me think twice about having that cup of tea in the afternoon. You know, 'cause I now know that if that's going to impact me, affect my sleep, et cetera...

AUBREY: Now, hold on here a second. What I need to point out is that these are two different kinds of tests. The caffeine test is based on her DNA, but the test to measure her response to starch and sugars is a blood glucose test. It's not based on her genetics. So this left me wondering, with an increasing number of personalized nutrition services on the market, how much can your genes really tell you? I put the question to Dariush Mozaffarian. He's the dean of the nutrition school at Tufts University.

DARIUSH MOZAFFARIAN: DNA is of course important, but it plays a pretty minor role.

AUBREY: He says so far genes only explain about 5 to 10 percent of the risk linked to diet-related conditions like type-2 diabetes and obesity.

MOZAFFARIAN: For basic healthy living, it's not about your genes. It's about your behavior.

AUBREY: This could change. Future advances could give new insight. But, he says, for now a personalized diet comes down to factors other than your genes.

MOZAFFARIAN: Such as your age, how much extra weight you're carrying, how you respond to eating starch or sugar. Really, it's these other things that are much more important.

AUBREY: Think about this example. Mozaffarian says cutting back on snack foods with lots of simple starch and sugar is good advice for everyone, but he says there are big differences in how well people respond. So when Kimberly Desjardine's glucose test showed she was not handling starch and sugar well, that was very useful information to her even though it didn't come from her DNA. So what's the potential value of these services?

MOZAFFARIAN: They get people to stop and step back and think about being healthy and eating a healthy diet.

AUBREY: Desjardine says this has been true for her. Her results nudged her to change her habits.

Allison Aubrey, NPR News.

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