Dave Asprey's elevator pitch sounds convincing: he was a computer hacker-turned-twentysomething dot com multimillionaire who had everything. But he weighed 21 stone and doctors warned he ran a real risk of dying of a stroke or heart attack.

He tried various diets — everything from low-calorie to high protein; Zone to Atkins, but apparently nothing worked. So Asprey set about trying to “hack” his own biology; to map out a system “in an attempt to find one little hole [I could] exploit in order to take over.”



By doing this Asprey says he discovered which foods (and drinks) were good for him - both physically and mentally.



The result is a diet high in saturated fat; one which holds that red meat is good, brown rice is bad, cuts out fruit, and that is coming to a bookshop near you on December 2 in the form of a publication called The Bulletproof Diet.

The only problem is, it flies in the face of everything we’ve been taught about what’s good for us and what isn’t. And perhaps unsurprisingly, the science behind it is questionable — at best.

Asprey’s Eureka moment began with his morning cup of coffee.

It was 2004 and he was in Tibet, learning to meditate and trekking in the Himalayas when something struck him about the local men accompanying him. They were of a much smaller build than him, but they could lift twice as much. And where Asprey’s clothing of choice for 11,000ft was a Parka, his compadres were in t-shirts.

The story Asprey likes to tell is that he went to a little guest house in the mountains and drank yak butter tea for the first time — the Tibetans’ answer to PG Tips — and he started to feel amazing. On his blog Asprey wrote: “It's the only thing that keeps you going at altitude, and the locals drink up to 40 glasses a day!”

That moment, he says, transformed his life. When he got home he tried blending regular butter in tea but it tasted terrible, so he blended grass-fed butter — which most appropriated yak butter - with coffee instead. Bulletproof Coffee was born.

Before long, thousands of people all over the U.S. were drinking organic coffee, replacing their milk with a stick of full-fat butter and blending in some coconut oil for good measure. (Conveniently, Asprey sells his own brands of both coffee and coconut oil from his website. One Bulletproof Coffee contains 500 calories and around 50 grams of fat.)

Google “Bulletproof Coffee” and you’ll see scores of blogs devoted to it. Vogue asked: “Is Bulletproof Coffee the new green juice?” And the forum on Asprey’s website shows in what high esteem his devoted followers hold him.

With the Bulletproof Diet, Asprey, a slim 41-year-old who lives in Canada, is moving on from your morning cup of java to your entire daily menu.

Upgrading your brain

According to his slick-looking Bulletproof website, Asprey read “countless thousands of research papers online, [spent] more than 10 years working with some of the world’s top health and nutrition researchers, [and read] over 150 nutrition books” to come up with his diet which he says will “not only make you stronger and leaner” but will also "upgrade" your brain and “reduce your risks of cancer, heart disease, stroke, diabetes, and Alzheimer’s.”

Asprey says he is living proof that it works.

“According to my world-class anti-ageing physician,” he tells us, “I’m in the lowest percentile for diabetes risk, heart disease, and cancer, despite being a high risk for all of those when I was 10 years younger. I have lower triglyceride levels [a type of fat] than most anyone I know.” He is claims to have increased his IQ by 20 points.

When we speak by phone, Asprey is on the 32-acre farm in British Columbia, where he lives with his wife, Lana, and their two children. I ask him to explain the Bulletproof Diet. What does he consume each day?

“I wake up and I have about 14 oz of Bulletproof Coffee,” he tells me. “I use about 2 tbsp of butter, and 2 tbsp of the extractive coconut oil.” If he eats lunch, he'll have several servings of vegetables, plus a protein “and all of it with butter.” Dinner, he says, is a similar affair: lots of veg, grass-fed steak, white rice.

The diet requires no calorie counting and no measuring. Followers eat when they are hungry and stop when they are satisfied.

'Fruit is candy'

What about fruit? I ask.

“The idea of having fruit for breakfast doesn’t make any sense,” he tells me. It contains high amounts of fructose, which will not give you a long-lasting energy boost and will, instead, cause food cravings. In fact Asprey rarely eats fruit at all any more (“every now and again, if it’s peak season.”)

"Fruit is candy and you should treat it like that," he says in a video on his website. "It will make you fat."

Asprey says sugar is a serious threat to our health Credit: Copyright (c) 2015 Rex Features. No use without permission./GARO/PHANIE/REX Shutterstock

Some of this theory is corroborated by nutritionists. Around the world, a growing body of expert opinion is warning that sugar, rather than fat, is the greatest threat to human health.

Respectable scientists such as Robert Lustig, professor of paediatric endocrinology at the University of California, are adamant that sugar doesn’t just make us fat and rots our teeth; it also causes several chronic and very common illnesses, including heart disease, cancer, Alzheimer's and diabetes.

Many of the New Year diet books this year focused not on fat or carbohydrates, but on sugar and the everyday foods (soups, bread) that contain high levels of sucrose.

However, the American Heart Association has stuck to its guns and still recommends a diet low in the type of saturated fats found in food such as butter and red meat.

“Decades of sound science has proven it can raise your ‘bad’ cholesterol and put you at higher risk for heart disease,” it says.

Asprey’s response is withering.

“The only thing I have to say to the American Heart Association is, ‘Shame on you’.”

In his opinion, consumers were badly let down in the Seventies when saturated fat was declared the number one enemy in the war against heart disease and low-fat foods were promoted as a healthy alternative.

(What the public weren't told was that, to compensate for the detrimental effect on taste, food manufacturers had substituted fat for spoonfuls of sugar.)

“When you’re an organisation like that, once you put something down as the truth it’s very hard to say, ‘Oh sorry guys, we were wrong,’” says Asprey. “I cannot wait for the American Heart Association to get sued for years and years of bad advice.”

Although he made his fortune in computing, Asprey says he has always been interested in nutrition. He remains chairman of an anti-ageing non-profit organisation called the Silicon Valley Health Institute which organises public lectures by “top experts in ageing and research and human performance and nutrition.”

But the institute's website reveals Asprey’s suspicion of mainstream medicine. Its last speaker was Dana Ullman, one of the world’s leading proponents of homeopathy.

What’s more, the research papers cited – such as “Cereal grains contribute to nutrient deficiencies” and “Brown rice (not white) prevents protein digestion” - are not altogether convincing.

Discredited

The one about cereal grains, for example, begins with a quote from the Bible and is written by a man called Loren Cordain, otherwise known as the author of The Paleo Diet, a health plan that involves eating only foods that were available to humans during the Paleolithic (or caveman) era, and has been widely discredited.

Another paper — “Switching from refined grains to whole grains causes zinc deficiency” — is a report of a 1976 research project featuring a study group of just two people. A third study - “Diets high in grain fibre deplete vitamin D stores” - is a 30 year-old study of 13 people.

A fourth - “Phytic acid from whole grains block zinc and other minerals” – is based on a 1971 study of people in rural Iran eating unleavened flatbread. Another is about insulin sensitivity in domestic pigs.

In other words, the research upon which the Bulletproof Diet stands is not exactly cutting-edge.

Prof Paul Garner, director of the Effective Health Care Research Consortium at the Liverpool School of Tropical Medicine, describes the Bulletproof Diet as “extraordinary” and the references Asprey gives to support it “unreliable … highly selective, many over 30 years old, of one or two patients.

“Very few of the references are of current research, and most is picking out studies that are of low or very low quality, none of which is put into the context of other research or systematic reviews.”

Garner says it doesn’t take a scientist to point out that a study of two people published in 1976 is suspect. “It’s just not credible to build this kind of commercial fiction on this.”

He does concede that the dangers of saturated fats have been over-emphasised, but insists they do still exist.

“I do think reduction in saturated fats in the diet is likely to have modest health benefits,” he says. “The reason you’re overweight is because you eat too much, drink too much, and don’t do enough exercise.”

It’s worth revisiting Asprey’s initial inspiration for his diet as well — yak butter tea, which he says formed part of a diet that enabled Tibetan Sherpas to scale mountains again and again, seemingly with ease.

In 2004, a study on the diet of Tibetan women found that Tibetans drank high quantities of buttered salt tea, consuming 12.5% more calories than the recommended daily allowance, and that these “high amounts of fat and caloric consumption resulted in increasing obesity among Tibetans, concomitantly increasing their risk for other health problems.”

The most common ailments were digestive disorders, upper respiratory diseases, tuberculosis, arthritis, joint pain, and back pain.

In 2011, a further study found abnormal lipid [fat] levels among highlanders. Sherpas had slightly lower levels of cholesterol, but another study found this was likely attributed to their metabolism of cholesterol at high altitude.

After British explorer Sir Ranulph Fiennes, who, together with Mike Stroud, became the first to cross the Antarctic unsupported, had a heart attack on a plane bound for Scotland in 2003, doctors looked at his diet.

On expeditions, he’d often consume upwards of 8,000 calories per day — and over half of that diet was made up of fat; lots of butter and chocolate. Fiennes was a notorious chocoholic before he changed his lifestyle.

Sir Ranulph Fiennes Credit: Copyright (c) 2007 Rex Features. No use without permission./ITV/REX Shutterstock

Asprey’s book makes other recommendations too. The best salt he has found, for example, is apparently mined in the US state of Utah — and the Himalayas — “from ancient seabeds, free of pollutants.”

He also advocates white rice over brown because brown rice, Asprey says, has more anti-nutrients in it.

“These grains didn’t evolve to be eaten as a food source. They evolved to reproduce; germinate. They cover themselves in naturally occurring anti-nutrients or pesticides. Brown rice has stuff that irritates our gut and that’s not the case with white rice.”

To back this up, Asprey links to a paper on the effects of brown rice on digestibility. But it’s based on a study group of just five people and statistically insignificant.

Half-baked

Prof Garner says it’s just not valid. “You can’t deduce anything from a study of five people. His opinion is backed up by any bit of research or study or half-baked idea in the literature for which there could equally be a counter-opinion. But he doesn’t take any of those into account.

“It may be that white rice is more digestible than brown rice. It may also be that people prefer white rice to brown rice. But that’s all that needs to be said.

"I know of no research that shows that eating brown rice results in vitamin or mineral deficiency. Brown rice includes proteins, vitamins and minerals, as well as fibre. And white rice is seen as a risk factor for developing diabetes.”

But this won’t dissuade Asprey’s cheerleaders. His book is interspersed throughout with affirmation from fans.

There's “Jose” who says the diet saved his life; “David,” who says it "taught me things I will take to the grave"; “Don,” who starts his day with Bulletproof Coffee "along with a glass of water with Himalayan salt and a 15-minute yoga posture”; and another “David” who has “got straight As for the first time ever because of my amazing focus from Bulletproof Coffee.”

Asprey also makes much of mycotoxins — naturally occurring mould that can affect crops — and how they’re poisoning our foodstuffs and are a threat to our health.

“I can tell you when I drink bad coffee — I don’t need a lab,” Asprey tells me. “If I drink bad coffee my head hurts. … So we ran a test.” Asprey says half his study group drank mycotoxin-free coffee for six weeks and half coffee made of beans from a local coffee shop. “And we found with statistical validity that people performed better on low mycotoxin coffee.”

But the study wasn’t peer-reviewed and published in a reputable journal, so its “statistical validity” can’t be confirmed.

Besides which, mycotoxins are found in all sorts of food — from raisins and grains to wine and peanut butter — and the amounts are generally too small to do us any harm. Asprey also claims mycotoxins make coffee taste bitter, but that’s down to naturally occurring tannins.

Overly simplistic

Dr Celeste Naude works at the Centre for Evidence-based Health Care at Stellenbosch University in South Africa. She says it’s overly simplistic to zone in on a single nutrient (like saturated fat or carbohydrates) in terms of establishing an exact health benefit or harm.

"Research shows that the overall combination of foods and nutrients we eat influences our health, not any single food, nutrient or food group on its own. Risks from saturated fat or refined carbohydrates are not mutually exclusive, but co-exist together in our diets, along with other risks related to, for example, sodium intake, fibre intake, total energy intake, intake of ultra-processed products etc.”

As for the list of studies on Asprey’s website, Naude says it's important to consider the whole body of available evidence, as well as the strength of that evidence. The bottom line, she says, is that scientific research findings are not always right.

“In fact they are seldom completely right and sometimes simply wrong. Many of the findings and observations will not be replicated by similar studies [so] providing a picture of the whole body of research.

"Yes, X may have been linked to Y in a study,” she says, “but critical questions to ask are, ‘What was the quality of that study? How large was the study? Was it done in humans? Was there a control group? What risks of bias were present?’”

Scientists often combine the findings of many studies in order to examine the entire body of evidence and arrive at more valid conclusions, she says. These “combination studies” are called systematic reviews.

In his book, Asprey tells us that he grew up in a “world of hard science” and that this has informed the way he looked at problem-solving. His grandparents, he writes, met on the Manhattan Project (which produced the first atomic bombs during the Second World War) and that his grandmother won a lifetime achievement award for her work in nuclear science. But Asprey is not a scientist.

The truth is — and it’s a truth people don’t like hearing — that if you want to live longer and improve your health and wellbeing, fad diets probably aren’t the answer.

Ben Goldacre, author of the book Bad Science which targets quack doctors and dodgy medical statistics in equal measure, puts it succinctly: “If you want to live longer you have to eat more fresh fruit and veg, get more exercise, watch how much alcohol you drink, avoid smoking, and watch your weight.”

But even then, you’re only reducing the risks. There are no guarantees. And that, to paraphrase a vegan former vice-president of America, is the inconvenient truth.

Buy The Bulletproof Diet by Dave Asprey from the Telegraph Bookshop