Diet advice changes with the decades. I remember eating cheeseless pizzas during the "fat-free" fad (thanks, Dad). And I'll never forget my high school cross country team's T-shirts saying "Eat Pasta, Run Fasta."
If we've learned anything from these fads, it isn't how to eat better. It is that there is no one-size-fits-all diet.
Now, a growing field called "nutrigenomics" aims to provide people with personalized lifestyle guidance, based on their DNA. But is this a breakthrough for nutrition science, or just another fad?
The "How to Eat" Formula
Melina Jampolis is a board-certified physician and nutrition specialist. She helps people reach their goals for fitness and body composition by giving tailor-made diet recommendations.
"Nutrition is all about context. We don't eat nutrients, we eat foods."
A few years ago, a 32-year-old vegetarian man came to her seeking advice on how to build muscle and burn fat.
After four months without progress, Jampolis suggested a Nutrigenomix test. Nutrigenomix is one of several dozen companies that offer genetic tests that purport to give insight into personalized, gene-based nutrition.
Much like 23andMe or Ancestry.com, by sending salvia to a lab, people can learn more about their genetic makeup. Some of the gene-based nutrition companies accomplish this by interpreting genetic data downloaded from 23andMe or Ancestry.
The analysis a subject receives is intended to help them learn which foods to eat to switch on or off specific genes. It can help them understand what foods might affect weight loss, immune functions, or their predispositions to disease.
Jampolis says the test results "confirmed her clinical intuition." Even though a plant-based diet is a healthy option, vegetarianism wasn't quite right for this man.
According to the test results, her client had a variation in his genetic sequence making it more challenging to build muscle. At the same time, his metabolic panel indicated that he should have fewer carbohydrates. With that combined information, Jampolis recommended that he eat less protein from beans and more animal protein.
For Jampolis, despite some of the companies' claims, the genetic test isn't a magic "how to eat" formula. She says there are many ways to interpret the results, so it is best used with a healthcare professional's guidance.
"As a practitioner, you're taking (a genetic test) in the context of a patient and bringing in multiple variables," she says.
The Wild West of Nutrigenomics
Nutrigenomix is one of the few nutrigenomics tests that must be administered by a medical professional. The founder, Ahmed El-Sohemy, specifically designed it that way to "restore credibility to the field."
El-Sohemy, also the nutrigenomics chair of the University of Toronto, says nutrition can be "vulnerable to snake oil science," and consumers should be cautious about genetic testing.
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"It was a bit of a wild west. There were some shady operators (...) linking their tests to ridiculously overpriced supplements that were not justified. It was really tainting the whole field. So, we established a test based on the robust science and decided to make it available only through healthcare professionals so that they can answer questions and concerns that people have around genetic testing."
In 2008, El-Sohemy discovered that some people's genetics could be causing them to eat more sugar regularly than others. He pinpointed the sugar habit to a variation in the GLUT2 gene — which became known as the "sweet tooth gene."
But El-Sohemy saw nutrigenomics companies extrapolate new meanings from his work — claiming their test for the sweet tooth gene would reveal how a body processes sugar and the optimal sugar intake level.
"That's nonsense. That's not what the study showed," he says, adding other examples of wild claims like genetic tests "for" an anti-inflammatory diet, or low-carb versus low-fat, where "the science just isn't there yet."
Nonetheless, he does believe the field is making progress. When he first launched the Nutrigenomix in 2012, their test only looked at seven genes. By 2018, they were investigating 72.
The Future of Personalized Food
In the past decade, more rigorous scientific research has been published with discoveries related to nutrigenomics. If "the science isn't there yet," when it comes to crafting personal diets from data, it is on its way.
David Mutch leads a nutrigenomics research program at the University of Guelph, studying diet-gene interactions, especially omega-3 dietary fats. He cites El-Sohemy's 2006 study on coffee and heart attack risk (which he did not collaborate on) as a prime example of robust nutrition science.
The study looked at a variant of the gene CYP1A2, which is associated with how well the body metabolizes caffeine. They found that having a particular version of the gene means that the body metabolizes caffeine slowly, and for this group, excessive coffee consumption may increase their risk of heart attacks.
Studies like this, Mutch says, are building a solid foundation for consumer nutrigenomics tests. If a person tests positive for that gene variant, then the recommendation would be to consume no more than two cups of coffee per day instead of the standard advice of a four-cup limit.
Mutch says that precision nutrition is about much more than DNA. It also takes into account gut bacteria (known as the microbiome), proteins, metabolites, etc. That is why he also supports nutrigenomics tests that are interpreted by a healthcare professional.
"Working with dieticians or healthcare practitioners is actually going to be the most efficient way to take that information you're getting and translate it into an actionable dietary plan. That's the challenge with nutrition. Nutrition is all about context. We don't eat nutrients, we eat foods."
The majority of chronic illnesses in the United States, such as hypertension, high cholesterol, obesity, and diabetes, are treated first with diet and exercise. However, research shows that patients are more likely to adhere to care plans tailored to their genetics instead of general dietary advice.
"This is a piece of the puzzle — to better understand ourselves, to better understand what we may or may not want to think about when we're making choices about the foods we're eating or the lifestyle choices we're making," Mutch says.
Maybe someday, to reduce the risk of heart disease, Alzheimer's, or hypertension, doctors will prescribe food as medicine — and know their prescription will stand the tests of time and science.
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