It was 2017, and Neil Thompson’s friend was about to be kicked out of the military for being overweight. Spurred into action, his friend announced that he was going on a diet and started to lose weight – and fast. Very fast. “In 20 days, he’d lost almost 10kg,” recalls Thompson, who works in IT for the navy. “So, I asked him, ‘How did you do it?’”

His friend explained that, while browsing online for a quick weight-loss plan, he had stumbled upon a Reddit thread about something called the “ketogenic diet”. People on the 1.4 million-strong r/keto subreddit posted about losing 25kg in a couple of months, while never feeling hungry and finding it easier to focus during their working days. However, the diet was, to put it mildly, contrarian in the same way that Brexit is “divisive”.

First, you almost completely eliminate carbohydrates. Low-carb diets are no longer considered radical – the macronutrient has steadily been falling out of nutritional favour for at least a couple of decades – but keto typically advocates an intake of less than 40g per day. (For context, most of us will hit that at breakfast.) Fruit is largely frowned upon, and there’s a strict cap on veg. Yes: fresh, wholesome vegetables.

If you assume that you’ll make up for those lost calories with generous servings of lean chicken, or copious whey shakes, you’re wrong. Next, you’re limited to about 100g of protein per day, though ideally less. What’s left? Lots of fat: marbled steak, oily fish, egg yolk, streaky bacon. Top it all with butter, olive oil or lard, then a scoop of smashed avocado. A classic keto diet provides 90 per cent of your daily calories from fat, 6 per cent from protein and 4 per cent from carbs. In short, it’s a giant middle finger raised at Public Health England’s “Eatwell Plate”.

But Thompson’s friend told him that the ketogenic diet, while bizarre, was rooted in science. The absence of carbs and the abundance of fat push your body into a metabolic state called ketosis, during which you burn fat instead of glucose. The 5ft 9in Thompson – who was, by his own admission, “a bit portly” at 90kg – was intrigued. His online digging led him to a podcast called The Joe Rogan Experience. Rogan, an American UFC commentator, comedian and self-described “silly bitch”, is well known for unpretentiously unpacking complex topics. In one episode, he interviewed top keto researcher Dom D’Agostino, a professor of physiology at the University of South Florida.

“It was interesting to hear a scientist talk about what he eats and why,” says Thompson. D’Agostino is not a salesman, and he did not create the diet (of which more later). But Thompson didn’t care about keto’s history. He just wanted to know if there was any substance to the hype. “I threw out all of my carb-heavy foods,” he says. “Then, I picked up as much bacon, grass-fed butter and steak as I could afford.”

Fact to Fad

If you’re like most fitness-minded people, you’ve probably dabbled with trendy eating plans at least once. But what makes a fad diet tip? That’s a question that Adrienne Rose Bitar, a nutrition historian at Cornell University, has spent her career answering. “Most diets start with some unhappiness we have with our lives and bodies,” she says. This makes us susceptible to simple, counter-intuitive messages that blame our dissatisfaction on a single culprit. Low-fat diet: fat is bad, so don’t eat it. Paleo: processed foods are bad, so stick to the kind of “pre-industrial” food that your ancestors ate.

With keto, you do exactly what your doctor (and likely mother) told you not to

With keto, you do exactly what your doctor (and likely mother) told you not to: eat the delicious, fatty foods and skip the vegetables. While this might partly explain keto’s rise in popularity, it overlooks a crucial aspect of the story. The keto diet, it turns out, was not developed to aid weight loss. It was designed for epileptics.

Fasting has been used as a treatment for epilepsy since at least 500BC. Your body usually runs on sugars harvested from the carbs you eat. You store around 2,000kcal worth of sugars in your liver and muscles. Your body burns through that in about 48 hours, which is when an evolutionary survival mechanism kicks in. Your body switches to its stored fat, some of which is converted to a fuel called ketones. This state is called ketosis (defined as registering 0.5 to three millimoles of ketones per litre of blood).

In the 1920s, Mayo Clinic doctor Russell Wilder started tinkering with a fat-centric diet that mimicked the effects of fasting by depleting the body of sugar. He tested his “ketogenic” diet on people with epilepsy and, ever since, it has been an effective treatment for seizures.

Weight loss entered the frame in 1972, when cardiologist Robert Atkins published his first diet book. The initial weeks of his eponymous diet plan centred on eating fat and very little carbs to induce ketosis, a “happy state… [in which] your fat is being burned off with maximum efficiency and minimum deprivation”. That was when keto first appeared on the radar of Stephen Phinney, an MIT-trained biochemist, who began researching its potential applications for endurance sports.

Then, in 1976, the “Last Chance Diet” took off. How it works is exceedingly simple: you drink a fat- and protein-rich concoction until you shed your desired amount of weight. The diet, created by osteopath Robert Linn, quickly spawned a lucrative industry, with £30m of the elixir sold in less than two years. You were supposed to consult a physician, who would ensure that you were getting the necessary vitamins and minerals – but most people didn’t bother.

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Your body can survive for a long time in a carb deficit, but it requires micronutrients. Robbed of minerals, it can’t perform certain crucial functions, like sending electrical impulses to your heart. Between July 1977 and January 1978, the US Food and Drug Administration received more than 60 reports of deaths among “liquid protein” users. The fallout included new regulations, and a negligence lawsuit for Linn. As for Phinney, he and his research on ketosis were, in effect, banished to academic Siberia.

Still, Phinney forged on, conducting studies that, for example, showed that liquid ketogenic diets with adequate nutrients wouldn’t cause heart problems. In 1988, Optifast emerged. Like Last Chance, it was a liquid diet, but with sufficient vitamins and minerals, plus a celebrity enthusiast in Oprah Winfrey. “She did it for four months,” says Phinney. “One day, she opened her show pulling a red wagon that contained 30kg of pig and beef fat. And she points to it and says, ‘That’s how much weight I’ve lost.’” Optifast immediately received more than 200,000 inquiries, and keto research surged in the early 1990s.

It was at this point that the diet was adopted by the hard-core bodybuilding underground, evolving into the version you know today. “I first heard about keto from this guy named Dan Duchaine,” says D’Agostino, a name cited by several other nutrition researchers interviewed for this story. (Duchaine, who died in 2000, was a two-time felon credited with promoting the steroid movement of the 1980s and 1990s, and reviving keto as a way for bodybuilders to drop fat quickly for competition.) Then, with the rediscovery of the Atkins diet in the 2000s, new generations – and perhaps you – warmed to the idea that low-carb could be a dietary tool.

THE VOORHES

Early Adopters

The scaling up of keto started with a study published by a San Francisco-based research centre in 2013. Scientists at the Gladstone Institutes found that a ketone, produced when you limit calories or carbs, can activate powerful anti-ageing genes. This keto diet, as the press release put it, “may one day allow scientists to better treat or prevent age-related disease, including heart disease, Alzheimer’s and many forms of cancer”. Nutritionally woke bio-hackers – interested in keto for fat loss, athletic performance, productivity and longevity in equal parts – began to self-experiment.

Among them was Tim Ferriss, the Princeton-educated, Silicon Valley-based podcaster and author. He’d dabbled in keto, writing that it’s “incredible for simultaneous fat loss and lean muscle gain, though perhaps needlessly complicated for non-athletes”. In 2013, he posted a video of Peter Attia, a longevity expert. In it, Attia talks about his battle with metabolic syndrome and how keto changed his health in ways that the conventional avenues of exercise and a vegetable-rich diet could not; he uses graph after graph to plot the positive impact on his triglycerides and blood glucose.

This sort of dietary evangelism is not without precedent. Diets have traditionally been religious: halal, kosher, Lent. As Bitar puts it: “Many diets were actually plans to purify the soul.” Now, in place of dogma we have data. But the sentiment is very similar: the right diet can make you not just trimmer but better. Following Ferriss’s endorsement, the number of people searching for the keto diet immediately doubled and continued to trend upward as other lifestyle gurus, such as Dave Asprey and Mark Sisson, jumped aboard.

Keto’s side benefits – a reduced desire to eat and increased focus – appealed to productivity-fixated, bio-hacker bros. “Keto does control hunger,” says Guyenet. The reason, he says, may be the extreme nature of the diet. “Carbs and fat together stimulate dopamine release and activate motivational circuits in the brain that drive us to eat,” he says. Consider ice cream: you find it so appetising because it’s both sweet and fatty. As for your promised mental clarity? This remains controversial. Any effect is probably due to eating less junk food, which can cause your blood sugar to rise and dip, impacting energy and mood.

As keto’s popularity continues to increase, the medical establishment has cautioned that – although the diet is considered safe when done correctly – the emphasis on saturated fat and the lack of micronutrients may affect your heart health over time. “We still don’t have enough long-term evidence on what happens to your body after 10 years of ketosis,” says nutrition researcher Stephan Guyenet. And an effective diet should be for life, not just for the summer.

Still, as the buzz around keto intensified, the claims became grander and more outlandish. In November 2015, Ferriss aired a podcast with D’Agostino. That was the tipping point, “the moment at which the diet entered the vernacular and zeitgeist”, says Andy Galpin, a performance researcher at California State University, Fullerton.

The episode’s rather hubristic title was “Dom D’Agostino on Fasting, Ketosis, and the End of Cancer”. Ferriss told the story of a friend with testicular cancer who would fast for three days to enter into ketosis before chemotherapy. D’Agostino noted that anyone with cancer needs medical supervision of their diet, but also said: “If you put your physiology into a state of fasting ketosis, that puts tremendous metabolic stress on cancer cells that are highly dependent for survival and growth on high levels of glucose and insulin. By subtracting them of those growth needs, they can [die], and you could potentially purge yourself of some precancerous cells.”

When asked about that statement, D’Agostino concedes, “This episode’s title is unfortunate,” but he points out that his research does suggest keto can help slow the progression of some cancers, though it speeds up others. “It’s much more complicated than ‘starve your cancer of sugar’,” he says. (Ferriss declined to be interviewed for this article.)

The Ferriss podcast was a gateway to The Joe Rogan Experience, and soon Rogan’s 30 million monthly listeners were learning about the “new” diet. As keto spread from Silicon Valley to the rest of the US, the emphasis shifted from self-optimisation to a key concern of the everyman working 40-hour weeks: weight loss.

No Dead Weight

Keto thrives on social media, in part because its swift results are so photogenic: you’ve likely seen the before-and-after shots on Instagram. “Short-term carb restriction can cause 3-4kg of almost immediate water loss,” says Galpin.

But ketosis isn’t the same for everyone, every time. It’s a moving target: you might only lapse into it when you drop your carb intake below 20g per day, or you might be able to eat 50g and still reap the rewards. To carry out the diet properly, you need to track your levels using a device. And since a single carrot can toss you out of ketosis, you need to quantify each meal, weighing your food and consulting a nutrition app to calculate the exact ratio of fats to proteins to carbs.

Hunger Management

Within a year of Rogan’s podcast, keto cookbooks flooded the market, searches for keto hit 17 million per month, and Orian Research estimated keto had become a £3.8bn industry. And because people on keto often lack nutrients such as vitamin C, magnesium and fibre, there’s been a supplement gold rush for brands behind products that make staying on the diet easier.

Which brings us back to Thompson and they key question: does keto work for weight loss? In the short term, yes. “But the weight-loss effects are driven primarily by appetite suppression, which in turn regulates calorie intake,” says D’Agostino. In other words, when you limit what you eat, you, well… limit what you eat. As scientific as many purport to be, weight-loss diets usually come down to eating less food.

Consider the results of a recent study in Jama journal, which found no significant difference in the amount of weight loss after one year between people on a low-fat diet and those on a low-carb diet. But the study’s results suggest an important fact about the efficacy of diets. Some people lost 30kg, while others on the same diet gained almost 10kg. Whether it works or not can depend on the individual.

Neil Thompson is now 12 months into his keto journey. “I’m down 23kg,” he says. His friend, meanwhile, bailed after three months, when a cross-country move made it hard to continue. “You can’t cheat, or it knocks you out of ketosis,” says Thompson. He prepares all of his meals at home. A go-to is steak topped with butter and asparagus spears.

Thompson plans to stick to the diet, even though it makes him “that picky arsehole” in social settings. “I recently listened to this debate on The Joe Rogan Experience with D’Agostino and Layne Norton, an expert who was more moderate,” he says. “The conclusion was that the best diet is whatever works for you. Keto works for me.”

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