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These Companies Are Selling Custom Diets—But Do They Work?

In pursuit of optimum health? A rising industry wants you to follow your gut.


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Consider for a moment how much time and energy and money the average American spends trying to optimize their diet. Whole30 says no dairy, added sugar, grains, or legumes. Those following paleo avoid anything that couldn’t be hunted or gathered, along with certain fats. The keto diet loves fats, to the extent that it suggests putting butter in your coffee. Jimmy Kimmel swears by intermittent fasting; Kate Middleton trusts a low-carb, high-protein plan extolled by Dr. Pierre Dukan. Now imagine you could avoid the $72 billion diet industry entirely and skip to the part where you knew exactly which foods worked for (or against) you—and all it took was just a single test, painlessly obtained within the comfort of your own home. Enter Viome, UBiome, Thryve, and Day Two—a clutch of new companies that are here to ask whether all the answers you’ve been looking for have been behind your very own navel all along.

The key, they say, is in your microbiome: the much-studied yet little-understood community of trillions of bacteria, viruses, and protozoa that live in and on our bodies. The system is so essential that some scientists speak of it as an additional organ and so transformative that those who have written about it, like Michael Pollan, say they no longer see themselves as a single person, but as a population, a constituency, of microbial organisms. How your microbiome deals with certain foods could influence your energy, your digestion, your weight, and your state of mind. All you have to do, as a user, is retrieve and send a sample of your stool, and these companies will use artificial intelligence to point you toward a nutrition plan tailor-made to your own requirements.

This is how I recently found myself sifting through my own waste. I had ordered a $149 microbiome testing kit from Viome, a company established in 2016 that claims customers in the hundreds of thousands. It arrived in a sleek cardboard box, with a logo that suggested a Swedish sci-fi film. Inside was a manual including instructions for both the retrieval of samples and online registration to view the results—numerical scores given to your metabolic fitness and inflammatory activity. “We take the guesswork out of eating right,” says Viome.

The biology involved provides some obstacles to these claims. First, your stool gives evidence from the colon and inner rectum, which is the very last section of the GI tract. It’s the denouement of the digestive story. Yes, doctors are doing amazing things with fecal transplants to affect the microbiome of people diagnosed with certain bowel diseases, like colitis, but that’s a world apart. A successful fecal transplant is akin to a better-running car after a fuelline replacement. What these companies are claiming they can do is overhaul the engine, fix the transmission, and train better drivers, all from a whiff of the exhaust. Put another way, “there’s lots of data beginning to be gathered,” says Jesse Shapiro, a professor of biology at the University of Montreal who specializes in microbial evolutionary genomics, “but what it means in terms of your health and what you can do with it is very limited.”

Second, your microbiome changes radically from week to week. Some experts say that 30 percent is unchanging (what they call your “core” microbiome), but even if that number is accurate, the bacterial population in your stool is almost certainly different from that higher up in the gut, like in the stomach lining, where those oh-so-important interactions with food first take place. Finally, there’s an identity problem. Two test subjects might have high levels of Bacteria X, which is known to metabolize fat. Except Subject 1 eats tons of fat and Subject 2 eats almost none. The same high level of one bacteria can mean opposite things in two different people.

Still, these kits are an almost irresistible offering at a time when, for the health-obsessed, what is put into our bodies has grown to take on equal importance to what we do with them. “All disease begins in the gut,” Viome says, quoting Hippocrates. “Imagine a world where illness is optional.” Day Two’s promotional material says it can “take your health to the next level.” Thryve claims its Gut Health program can “supercharge” weight loss, increase your energy, help with your immune system, and improve your mood.

Which brings up an important point: Despite the scientific jargon and, in the case of Viome, safety approval from the FDA, these kits are not clinical. There’s information to be had, “but I’d call it recreational,” says Shapiro. “You might do the test, and it says you are lower than the average in a certain kind of microbe that feeds on fiber. So maybe you can add more varieties of more fiber to your diet. Eat more vegetables.” Shapiro compares it to a Fitbit: “Maybe it’s motivational.” There are also very real privacy concerns regarding the DNA in the samples, a breadth of which is necessary for the AI these companies use to function accurately, but once collected could be hacked, used by law enforcement, or sold. (At-home genetics test 23andMe just inked a four-year-deal with GlaxoSmithKline, a pharma giant, for $300 million.) Several, like Onegevity and LunaDNA, allow customers to decide whether or not they can use their DNA, and give shares or some proceeds in exchange for data. Viome founder Naveen Jain says the company keeps personal information and DNA data in two different places, but that sharing information is the point. “It only works if all of humanity comes together,” Jain says. “Let’s join hands together to solve this problem.”

The actual “problem” we’re confronting with these home microbiome kits may be less about chronic disease, or even diet, than one of our own making. To perfect our diets would be to remove one of life’s major preoccupations—namely, the acquisition of energy, which we require to exist—and to instead use nutrition to engineer what we imagine to be our best possible, or most optimized, selves. As it stands, this generation of microbiome tests is just one in a series of steps required to learn more about your gut. “It’s just isolated microbiome,” says Dr. Eric Topol, a professor of molecular medicine and executive vice president at Scripps Research. “You have to be able to connect the dots, the whole mosaic.” That means other inputs, like physical activity, sleep, and diet, plus factors such as DNA and blood testing. While these test kits fit nicely into this narrative, the story of our health, and how diet might affect it, remains much too big to fit in one neat little box.


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