DNA-Based Diet Advice Is Big Business With Little Scientific Support

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If you believe nutrition scientists, healthy eating is a simple — if difficult — pursuit: Eat lots of vegetables, fruit, whole grains, seafood, and legumes, and limit your intake of red meat, processed foods, refined grains, and anything with lots of added sugar.

This simplicity gets easily lost, though. Thanks to expensive marketing campaigns by big food companies, media that thrives on drama, and a rotating door of fad diets, what is and isn’t considered “healthy” feels as if it’s in constant flux. Fat, sugar, salt, cholesterol, dairy, gluten, and grains have all wrestled for the title of public health enemy no. 1.

For years, I managed to ignore the inflammatory headlines and shocking new studies. While friends and family routinely eliminated whole food groups only to “reintroduce” them weeks later, I kept my head down and worked on upping my vegetable intake and cutting back on processed foods.

But I wasn’t immune, either. A few years ago, thanks to the ease and availability of genetic sequencing, a new category of health startups began to form. The founding premise was seductive in its clarity: Standard dieting advice is too broad to be effective. Instead, if we want to truly nourish our bodies (and, by extension, actually lose weight), we should be following personalized eating plans based on our unique genetic and microbial makeup. It’s the same magical thinking that has popularized hundreds of bizarre eating plans–maybe it’s just a matter of finding the right diet–wrapped in a layer of sophisticated-sounding science. Today, there are dozens of companies that send users personalized dietary advice based on their genetic data. (A nonexhaustive list: Habit, Vitagene, EmbodyDNA,uBiome, Viome, Nutrigenomix, LifeNome, and DNAFit.)

While the specifics vary, the process typically begins with users sending in genetic samples to be sequenced and analyzed. The collection process ranges from the relatively simple to the elaborate. uBiome, which sequences gut bacterial populations, asks for a small fecal sample, while Habit, a Silicon Valley-based startup that creates personalized eating types based on “an individual’s unique biology, metabolism, and personal goals,” has users send in multiple blood samples, both before and after chugging a 950-calorie milkshake. Prices for these services run the gamut from just under $100 to $300.

At the time, I was particularly susceptible to this sales pitch. As if overnight, my clothes had all become too tight. I diligently went about replacing my sandwich lunches with salads, and increased the number of hours I spent at the gym, to mixed results. (Yes, I got faster on the treadmill, but I also frequently found myself in the kitchen at 2 a.m. eating cinnamon oatmeal.)

After months of this, the number on the scale hadn’t budged. The reason, I eventually convinced myself, wasn’t a naturally slowing metabolism (I had just entered my late 20s), chronic job stress, or all that early-morning oatmeal. Instead, I decided my gut bacteria was to blame (I’d recently taken a course of antibiotics to quash a strep throat flare-up). Or maybe the vegetable and whole grain-heavy foods I diligently consumed each day were, for my unique genetic and microbial composition, the equivalent of sugar cookies.

While I didn’t go as far as sending in my stool or spit samples to get sequenced, I did a lot of Googling, and read a lot of glowing testimonials from people like Anne M., an insurance professional/mom who tried dieting only to watch the number on the scale go up. Frustrated, she turned to Habit. Since starting her new, curated food regime, Anne M. has lost weight: “I’m now eating the right foods for my individual biology,” she writes in a post featured on the company’s website.

It’s easy to get pulled in by this type of anecdote. The logic is compelling: Maybe we all just need to figure out the types of foods that agree with our genetics, and the pounds will finally fall off.

Sadly, we shouldn’t hold our breath. A 2015 meta-analysis that examined the available research on this category of startups found that “solid scientific evidence is currently lacking.” The science behind these startups is fundamentally flawed, says Aaron E. Carroll, a pediatrician, professor of pediatrics at Indiana University School of Medicine, and author of The Bad Food Bible. There’s no evidence that some people respond better to high-fat diets while others are more receptive to diets packed with protein or complex carbs. “It doesn’t exist,” he says. Even if it did, “there’s no evidence we could detect it” through DNA sequencing. Metabolic illnesses and disorders such as celiac disease or lactose intolerance aside, humans’ genes are very similar. We evolved to be able to eat the same foods.

When I mention this to Josh Anthony, Habit’s science adviser, he directs me to a three-part series by the American Council of Science and Health that “shows people respond to micronutrients very differently.”

The company also sent over two studies to support its methods. The first is simply a validation that Habit’s collection method (i.e., having users take their own blood samples before and after consuming a milkshake packed with fats, carbs, and sugars) is scalable. The second, in which Habit is not mentioned, is a review of personalized nutrition science. In other words, the effectiveness of Habit’s nutrition plan has yet to be tested in a clinical trial. After reviewing both studies, “I have yet to see them say, ‘We changed a diet and it made a difference,’” says Carroll. (The company said two clinical trials are in the works, but declined sharing any specifics.)

CEO and founder Neil Grimmer stresses that Habit’s dietary advice is based on more than genetic data. In addition to incorporating blood and genetic biomarkers, the company takes users’ preferences, goals, and, yes, habits into account to design a personalized diet plan. It’s a “systems-based approach,” he says, that provides “a holistic picture of what’s going on inside yourself.”

Dietary advice based on microbiome sequencing rest on even less tangible ground. Lita Proctor is the director of the Human Microbiome Project, a federal project tasked with sequencing the genetic material of bacteria in humans. Nearly a decade into the endeavor, “I couldn’t tell you what a healthy microbiome looks like,” Proctor says. “We haven’t figured out which properties to measure.” That’s not to say the microbiome won’t lead us to exciting and potentially momentous discoveries–it’s been linked to everything from cancer, to mental illness, to metabolism. But so far, the research hasn’t moved much beyond a collection of intriguing but nonlinear connections.

For example, scientists have found a series of differences between healthy people’s gut bacteria populations and the populations of individuals suffering from bowel diseases or Type 2 diabetes. “But we still need time to investigate these biomarkers,” Proctor says. This will take years, and likely decades: In addition to identifying and categorizing the trillions of microbes that reside within us, researchers need to understand how they interact with one another.

If Proctor doesn’t know what a healthy bacterial population looks like or how it acts, it’s hard to get onboard with a startup like uBiome, which willtell you how your microbiome is functioning for $89.00. (uBiome did not respond to multiple requests for comment.)

Improving one’s microbial composition is possible,  just like losing weight is possible. But you don’t need to send in a stool sample to do it. “People can take charge of their health by improving their diet,” Proctor says. Gut bacteria feeds on fiber, so increasing one’s intake of vegetables, fruits, and foods high in fiber helps encourage microbial diversity. But the process is slow and opaque. Concrete milestones are hard to come by. “It isn’t sexy,” she says. “There’s no quick fix.”

Carroll would agree. Gut health and metabolic health are governed by boring principles that have nothing to do with fancy sequencing technology, he says. They include practicing moderation, eating more fruits and vegetables, and cutting back on processed foods — in other words, the traditional advice for losing weight and staying healthy.  While it’s often difficult to stick within these parameters, they also aren’t that narrow. “You can eat a variety of diets and still be healthy,” he says.

In a way, I wish Carroll and Proctor were wrong. How great would it be if we each had a diet hack embedded in our genetic code, waiting to be unlocked via a spit swab?

But alas, that’s not how life works: There are rarely shortcuts. “I know people in their 40s who have amazing physiques. They’re on restrictive diets and work out regularly,” Carroll says. “It’s hard!”