At first, the cravings were like “a drug withdrawal,” Jay Wortman recalls.

Lying on a hotel bed in Ottawa one night, he’d had to white-knuckle his way out of eating Ferrero Rocher chocolates he’d spirited off a flight. A recent Type 2 diabetes diagnosis had prompted the Vancouver-based family medicine doctor to cut out nearly all carbohydrates — sweets, pasta, bread, even fruit — in an attempt to manage his blood sugar while he waited to start medication. But he couldn’t stop thinking about those chocolates, or his favorite breakfast: waffles doused in syrup. “I think I was a full-fledged sugar addict,” he says.

Four months later, the sugar pangs had eased. He got through the early weeks by stocking up on artificial sweeteners and focusing on how much his 2-year-old son needed a healthy dad. With sugar off the table, he says, all that was left was “the non-carby foods” — bacon, eggs, steak, and vegetables. Soon, he started sleeping better and feeling less fatigued. Weight was coming off at the rate of a pound a day, until he was down 30 pounds and no longer overweight. “I had to get my pants taken in,” Wortman says. “And then I had to get them taken in again.”

More than 16 years later and still following the ultra-high-fat, low-carb regimen that’s become popularized under the name keto, Wortman has never taken a diabetes drug. He hasn’t needed to. He feels stronger and is skiing the most ambitious slopes of his life. “At 68, I’m far fitter than I was at 52 when [my diet] started,” he says.

Transformation stories like his — and the thousands of seemingly hyperbolic claims of dieters losing dozens of pounds, complete with Instagrammed before-and-afters — have made keto the biggest diet phenomenon today. The most Googled diet of 2018, it has eclipsed household names like Weight Watchers (now known as WW) and the other low-carb regimens, Atkins and Paleo.

Keto is a Silicon Valley life-hacking fixation (see author Tim Ferriss’s keto videos), a Hollywood trend (see Kourtney Kardashian’s and Halle Berry’s keto journeys), and fodder for numerous online communities. Devotees can meet at low-carb keto cruises, keto conferences, and keto cafes. While there’s no leading figurehead, a cadre of evangelists sell books and pseudo-medical supplements and devices to help dieters check whether they’re truly in “ketosis,” the holy grail fat-burning state keto dieters are after.

Beyond all the hype, the chance that keto — a minimalist variation on the diet promoted by cardiologist Robert Atkins — can solve the obesity crisis is vanishingly slim. On average, low-carb diets look a lot like others when it comes to long-term weight loss: Most people can’t stick to them. There’s tremendous variation in how humans respond to nutritional and dietary tweaks, and let’s not forget that the promises keto boosters now make are reminiscent of the overhyped claims that fueled the recent gluten-free craze.

But how do you explain results like Wortman’s? He expected that avoiding carbs would help manage his blood sugar in the very short term, not that his other diabetes-related symptoms — thirstiness, frequent urination, and blurred vision — would vanish. And he definitely didn’t anticipate that the diet would allow him to control the disease long-term, without any medication.

Keto might not be an obesity panacea, but it would be a mistake to dismiss the diet as just another fad, in part because of results such as Wortman’s. Along with all the dubious keto supplements and the weight loss books has come a growing body of science exploring keto as a potential foil for Type 2 diabetes and other illnesses. It’s part of a fascinating broader examination of how we might use nutrition to treat disease.

“It’s anti-establishment”

Keto isn’t just low-carb — it is practically no-carb. Its followers avoid ice cream and pizza, as well as whole grains, fruits, and legumes such as brown rice, apples, and lentils. No bakery-fresh bagels, homemade apple pie, birthday cake, or even juicy watermelon.

But what people eat in America — and around the world — is carbohydrates. They account for roughly half the calories on average in the American diet, come highly recommended in national nutrition guidelines, and feature prominently in the traditional diets of everyone from pasta-munching Italians to rice-loving Indonesians.

According to the United Nations’ Food and Agriculture Organization, of the world’s more than 50,000 edible plants, “Just three of them, rice, maize and wheat, provide 60 percent of the world’s food energy intake.” All three of those staples are carbs.

To follow a keto diet is to reject this culture and history. And while keto forbids processed junk foods — something common to just about every diet — it also severely limits the fruits, grains, and legumes suggested by the US Department of Agriculture as essential parts of a healthy diet. Keto adherents believe the conventional nutrition wisdom is not only wrong but actively harmful.

This rejection of mainstream thinking helps explain why keto went viral at this moment, and why it’s more than just a diet. It’s a cultural identity.

Take Wortman. He’s been on two of Jimmy Moore’s low-carb cruises, sailing across the Caribbean, downing steak after steak. His wife started keto shortly after he did and remains on the diet. He calls their daughter, who was born seven years into their keto lifestyle, “a product of a keto gestation.”

The diet didn’t just change Wortman’s life; it changed how he thought about medicine and nutrition. He believes there’s a conspiracy by a “matrix of agendas” to promote a plant-based diet. The “whole fiber thing is a myth,” he tells me. He also thinks the concerns about a meat-heavy diet’s impact on the planet — that cows produce too much methane — are hugely overblown (they aren’t), and that the link between cardiovascular disease and saturated fat has been “debunked” (it hasn’t).

In a time when black is white, up is down, and discussions of fake news dominate the news cycle, it’s no accident that keto went viral, says Alan Levinovitz, a James Madison University religion professor who studies diet beliefs. “It’s anti-establishment,” mirroring other strains of rebelliousness in our politics, he says. He experimented with the carnivore diet (a form of keto) and says he experienced no health improvement.

Americans are living in the aftermath of the low-fat experiment — where the public learned about guidelines and studies that have often been muddied by food industry interests. With its emphasis on fat, keto is the antidote to the Snackwell’s era. You can gorge on butter and bacon and stay in ketosis. It’s the perfect fuck-everything-you-know-about-nutrition diet.

A diet to heal disease?

Keto’s potential to heal has captured the imagination of people like Columbia University oncologist and author Siddhartha Mukherjee, who has been studying the diet’s effects on cancer. “We are trying to steer clear of any diet crazes,” he says. “For me, it’s thinking of the diet as a tool or drug,” one that may work when used in tandem with traditional cancer medicines in “a very particular population of cancer patients.” Keto’s effects on insulin and glucose levels — and how they may interfere with cancer cell growth — are what intrigue Mukherjee and other scientists.

He’s only tested the cancer hypothesis in mice. And he has other concerns, echoed by many in the medical field, including that keto may not be safe for the cardiovascular system since it can drive up cholesterol levels.

Wortman, the keto evangelist, is gratified that other doctors are at least opening their minds to keto as a therapy, something he didn’t expect to happen in his lifetime. After his high-fat and -protein diet controlled his blood sugar, he started reading about keto in Atkins’s books and scientific papers and became convinced of its potency.

The diet’s potential for treating Type 2 diabetes is the aspect of keto that has long obsessed Wortman. More than a decade ago, he started lecturing on the subject at medical conferences, only to be lambasted. Other health professionals believed the high-fat regimen would damage people’s kidneys, arteries, and brains.

Wortman felt vindicated when, this spring, the American Diabetes Association came out with a consensus statement — intended as guidance for doctors across the country — suggesting a very low-carb diet could be a nutritional treatment option for some patients with diabetes.

Today, Wortman prescribes keto to all his patients who have Type 2 diabetes. (The standard medical interventions include weight loss, exercise, medication such as metformin, and insulin therapy, as well as regular blood sugar monitoring.) He’s even experimented with using the diet to treat northern British Columbia’s aboriginal people, who are disproportionately diagnosed with Type 2 diabetes. Though he never published anything on the experiment in a scholarly journal, it was the subject of a 2008 Canadian Broadcasting Corporation documentary. “People lost weight, improved their diabetes, and got off their medications,” says Wortman, who does not profit from advocating for the keto diet.

“The obvious failure of the conventional approach has also been getting too big to ignore,” he adds. “I often say to my patients and colleagues now, ‘What’s the most important thing you do about your health? It’s your diet.’”

The burning question

The reason for shunning sugars is that eating more than the equivalent of a slice or two of bread each day can knock dieters out of ketosis. Dr. Atkins reportedly liked to say that ketosis is “as delightful as sunshine and sex.” (With his four-phase plan, he promised to help people “stay thin forever” by eating more fat and fewer carbs — the same way the now-popular Keto Reset Diet book promises to “burn fat forever.”)

To understand how ketosis works, consider how the human body uses fuel. On a typical high-carb diet, we’re fueled primarily by glucose (or blood sugar), much of which we derive from carbohydrate-rich foods. When we eat a bagel or a bunch of grapes, for example, the glucose levels in our blood rise, and the pancreas secretes insulin to turn glucose into an energy source, moving it from the blood into our cells.

But the body only evolved to store enough glucose to last a couple of days. So if we forgo eating carbs, it finds other ways to keep going.

One of those ways is a process called ketogenesis. In ketogenesis, the liver starts to break down fat — both from food and from the reserves stored in our fat tissue — into a usable energy source called ketone bodies, or ketones for short. Ketones can stand in for glucose as fuel when there’s a glucose shortage. Once ketogenesis kicks in and ketone levels go up, the body is in ketosis and burning fat instead of the usual glucose. (Whether this actually leads to increased calorie burn or fat loss is a matter of scientific debate.)

There are a couple of avenues into ketosis. One is through fasting: When you stop eating altogether for an extended period of time, the body will ramp up fat burning for fuel and decrease its use of glucose (which is part of the reason people can survive for as long as 73 days without food).

Another way to reach it is by making your body think it’s fasting — by eating only about 20 to 50 grams of total carbs per day. At the low end, that’s equivalent to a slice of bread or a small potato.

People on a keto diet generally aim to get about 5 percent of their calories from carbohydrates in foods such as berries and salad, about 15 percent from proteins like salmon and sardines, and 80 percent from fats including coconut oil and avocado. And ketosis is a quantifiable state. Dieters can measure their ketone levels with blood tests, breathalyzers, and urine strips (with varying degrees of accuracy — blood tests are considered the gold standard for now).

This data-driven aspect is part of what appealed to Ethan Weiss, a University of California San Francisco professor of cardiovascular research. Initially, he was skeptical when he was invited to consult for Virta Health, a company selling lifestyle counseling on ketogenic diets for Type 2 diabetics. A second-generation cardiologist, he says his family had “nothing that resembled fat in the house” when he was growing up.

The more he learned about keto, however, the more intrigued he became. He says he was excited by “the idea that we can give [patients] an option that’s going to get them off medication reliably. The only other intervention that’s done that was bariatric surgery,” he says.

Eventually, Weiss co-developed a breath sensor, called Keyto, to help people track how their diet affects their ketone levels. Playing around with the prototype, he realized he’d made the diet a kind of game. “I was trying to see if I could get my ketone levels to go up. And because I’m naturally competitive and like games, I got obsessed.”

Within two months, he dropped nearly 16 pounds he hadn’t intended to lose and saw his blood sugar levels, which had been high, normalize.

Still, he concedes there’s a lot we don’t know about the effects of the diet. “There are two questions: Is it safe to be in ketosis long-term? And is there something else about this diet that’s potentially dangerous or harmful long-term? We can’t really answer either one in a rigorous way today,” he says.

One concern is that some people on keto will see their cholesterol levels increase, which is linked with a heightened risk of heart disease. In a recent op-ed criticizing low-carb evangelists for their “cheerleading,” Weiss wrote of the cholesterol problem: “It’s a classic issue of balancing benefits and risks, one complicated because it isn’t clear if, how much, or in whom an increase in cholesterol even matters. That’s why there is general consensus that rigorous clinical trials are needed to answer this critical question.”

Other doctors, writing in JAMA Internal Medicine, list “keto flu,” cardiac arrhythmias, constipation, and vitamin and mineral deficiencies among keto’s documented side effects in the pediatric scientific literature. But the diet’s greatest risk, they write, may be the opportunity cost of not eating enough high-fiber, unrefined carbohydrates.

I ask Weiss why he’s so excited about keto, even willing to promote it, given those risks, and the fact that sustained weight loss on keto doesn’t look all that different from other diets. “[We] can’t let perfect be the enemy of great,” he answers. “That is, what we are doing now sucks.”

The frontiers of keto science

Oncologists are also looking past keto’s big unknowns and exploring the potential benefits of the diet as part of cancer therapy. While they warn that it’s far too early to prescribe the diet for any specific cancer type, they’re excited about the possibilities.

For a study published in 2018 in Nature, Mukherjee and his co-authors tested whether PI3-kinase inhibitors — a class of drug used to treat cancers, which has the side effect of driving up blood sugar and insulin levels — would perform better in mice when they also ate a keto diet or took a drug that suppressed insulin levels. The idea they wanted to test, Mukherjee explained on Weiss’s keto podcast, was: What if “the drug causes a physiological side effect — high sugar, high insulin — and that high insulin is now what is bringing the tumors alive again ... like a malignant circuit.”

In the study, the combination of the drug and the diet shrank 12 types of tumors in mice — even pancreatic cancer, which is very difficult to treat in humans. But keto caused the leukemia to worsen, meaning researchers still need to work out where the diet is helpful and where it’s harmful.

Marcus DaSilva Goncalves, a co-author on the study and endocrinologist at New York’s Weill Cornell Medicine, says we’ll learn more from a human trial, scheduled to start later this year, that will build on the mouse research.

For now, it’s way too early to know whether this research will translate to humans, despite all the YouTube videos and blogs suggesting that sugar “feeds” cancer. “We are in the Stone Age of understanding which diet is best for each type of cancer site,” Goncalves said.

He’s also concerned about heart health. “We don’t know what it’s doing to cardiovascular risk factors. But cancer’s unique — people are willing to accept a more hazardous condition in order to cure the cancer.”

Another new area of research is using keto to prevent and reduce the severity of flu. In November, researchers published an intriguing paper in the journal Science Immunology that found that a keto diet protected mice from lethal influenza A infection and disease. The study authors have said they don’t know if it could work in humans, but they encourage more research.

Much better-established are keto’s effects on epilepsy. For nearly a century, doctors have been prescribing the diet to treat epilepsy, an idea that came about in the 1920s, when researchers observed that people who fasted experienced fewer seizures. Researchers still aren’t sure why the diet can work, but a few mechanisms have been proposed, including making neurons more resilient during seizures. And today, studies have shown that children and adults whose epilepsy doesn’t respond to medications seem to experience a pretty large reduction in seizures when following a ketogenic diet.

That doesn’t, however, mean that the diet works for other conditions. There are still many questions about even the most talked-about keto applications, such as keto for Type 2 diabetes. While researchers have found the diet can reduce people’s hemoglobin A1C (a measure of blood sugar) and their reliance on medication, the effects tend to wane after one year.

Virta Health, the keto counseling company Weiss consults for, recently published data from a two-year evaluation of the Virta program. Through telemedicine, Virta’s clients get nutrition support and health coaching about how to prepare low-carb foods and stick to the diet. In the trial, people’s A1C and weight crept up between one and two years — but 38 percent saw their diabetes reverse and 15 percent were in remission. “Those results are dramatically better than anything else anybody’s published at two years with diet or lifestyle regimen,” Steve Phinney, a founder of Virta who has been studying (and living on) keto for decades, says.

Skeptics, such as the cardiologists turned diet gurus Dean Ornish and Joel Kahn, argue that keto’s potential heart risks are too great. Others note that it’s not clear whether it’s the keto diet itself or the weight loss it can induce that helps control Type 2 diabetes.

To begin to answer the latter question, Phinney and his colleagues ran a study that cycled 16 patients through a low-carb (keto), moderate-carb, and high-carb diet during four-week periods, with two-week reset periods in between. During the diet, the participants were fed enough to keep their weight stable. At the start of the trial, they all met diagnostic criteria for metabolic syndrome, a constellation of conditions — excess fat in the abdominal area, high blood sugar, low HDL (or “good”) cholesterol, and high blood pressure — that are linked to an increased risk of heart disease, stroke, and Type 2 diabetes.

The results were just published in the journal JCI Insight. After one month on the high-carb diet, one of the 16 people no longer met the criteria for metabolic syndrome. On the moderate-carb diet, three of the 16 reversed their metabolic syndrome. On keto, that number rose to nine out of 16. This suggests that it’s carbohydrate restriction, not weight loss, that helps control metabolic syndrome, including high blood sugar.

The study will have to be replicated. It’s also worth noting the high-carb group ate a lower-quality diet (with foods such as marshmallow fluff and barbecue sauce) while the lower-carb groups stuck to whole foods, which could have muddied the results. And it was funded by a grant from Dairy Management Inc. and the Dutch Dairy Association, and co-authored by researchers with a financial stake in showing keto’s benefits.

But Phinney believes the work is nothing short of revolutionary. “A guy named Thomas Kuhn pointed out that scientific revolutions don’t happen overnight, they happen over time,” he says. “We’re using a non-pharmaceutical, very powerful tool to hopefully halt and turn back an epidemic that is threatening our ability to provide health care because it’s such a dramatically expensive disease.”

And there are other ways the diet may be used. Researchers are currently exploring the benefits of keto for Type 1 diabetes. There’s preliminary research suggesting an ultra-low-carb diet could have a role in treating neurodegenerative diseases, like Alzheimer’s and Parkinson’s. A lot of the brain research, however, was done in mice or cells, so we still need evidence of human response. When we have better studies, keto might look as ineffectual as gluten-free — or maybe it’ll be the diet miracle we’ve been hoping for. That is, if we can stick to it.

CREDITS

Editor: Eliza Barclay

Visuals editor: Kainaz Amaria

Designers: Amanda Northrop and Christina Animashaun

Copy editors: Tanya Pai and Tim Williams

Cover designer and graphics: Javier Zarracina

Photographer: Scott Suchman for Vox

Food stylist: Lisa Cherkasky for Vox