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

Jan 22, 2018
Originally published on January 22, 2018 8:56 am

The idea that each of us has a unique nutrition blueprint within our genes is a delicious concept.

Perhaps, this helps explain the growth in personalized nutrition testing and services such as Habit, Profile Precise and Nutrigenomix.

So, what exactly can these tests tell you?

Kimberly Desjardine, 52, decided to try Habit last fall. She's very active. She plays tennis, practices yoga and walks regularly. "But as I've gotten into my 50s, it's been increasingly harder for me to keep those extra few pounds off." She was intrigued by the idea of diet advice based on her biology.

To get the process started, she used an at-home test kit to take blood and DNA samples. The kit instructs customers to take blood samples both before and after drinking a sugary, high-fat, test drink.

Once her samples were analyzed, she was categorized by Habit as a "Protein Seeker." It's one of seven diet types including Fat Seeker, Balance Seeker, and Range Seeker that Habit assigns.

"For me, the biggest 'a-ha' coming out of the test was that ... I need more protein than the average person," Desjardine says. Part of the testing showed that her response to starch and sugar was not ideal, so high-protein foods should be at the center of her plate. This meant she cut back on breads and other starchy foods, too.

The testing also showed that Desjardine has a variant of a gene that makes her sensitive to caffeine. "The information makes me think twice about having tea in the afternoon," Desjardine says. She had already realized that too much caffeine could keep her awake, but the new information confirmed her instincts. "The knowledge is good. It just gave me that extra 'a-ha.' "

The Habit approach is based on a bunch of different types of tests, not just genetic tests.

For instance, the caffeine test is based on DNA. But the test that revealed Desjardine's response to starch and sugar came from the fasting blood test that measures glucose response. So, that one is not based on DNA.

"Your genes are part of it," explains Neil Grimmer, the founder and CEO of Habit. In addition to the caffeine sensitivity gene, Habit also analyzes a gene linked to the digestion of lactose, as well as a variant of a gene known as FTO that may predispose people to weight gain.

But Grimmer acknowledges there are limits to what DNA tests can reveal. "So, we take a systems approach. It's a variety of tests we integrate together to give you the recommendation."

Experts say, when it comes to diet advice, it's misleading to say that the blueprint is our genes.

"DNA is important, but it plays a pretty minor role in making personal decisions about food," says cardiologist and dean of the Friedman School of Nutrition Science and Policy at Tufts University Dariush Mozaffarian.

So far, genes only explain about 5 to 10 percent of the risk linked to diet-related diseases such as obesity and type-2 diabetes, he says.

"For basic healthy living, it's not about your genes, it's about your behavior," Mozaffarian says.

Future advances could give new insights, but for now, a personalized diet mostly comes down to factors other than your genes. "It's your age, how much extra weight you're carrying, how you respond to eating starch [and]/or sugar, and potentially even your microbiome, that are much more important," says Mozaffarian.

He says cutting back on snack foods and junk foods that contain lots of refined starch and sugar is good advice for everyone. But, he says, there are significant differences from person to person in blood glucose responses after eating these foods.

So, when Kimberly Desjardine's tests showed her response to these starchy, sugary foods was not great, this was useful, actionable information for her. She says it's nudged her to change her habits for the better.

So, while the marketing of DNA-based nutrition advice may have gotten ahead of the science, Mozaffarian says these personalized services can be beneficial.

"The real value they have is that they get people to stop, and step back and think about eating a healthy diet," Mozaffarian says.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.

DAVID GREENE, HOST:

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. Transcript provided by NPR, Copyright NPR.