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The Bulletproof Diet is everything wrong with eating in America

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When I first heard about the Bulletproof Diet — the "revolutionary" plan for weight loss — I tried to turn a blind eye. I really did.


But then, there were rumblings around the newsroom. "My Silicon Valley Facebook friends are posting about it a lot," said one colleague. Another wanted to know whether there was any science to the claims that butter-laden coffee could actually help achieve a new level of mental clarity. When the "cult" turned up in the New York Times, my editor said we should be writing about it, too.

I've spent a lot of time thinking about diet and, unsurprisingly, came to Bulletproof with a skeptical eye. But even I was blown away by how science-y it is. The Bulletproof Diet is like a caricature of a bad fad-diet book. If you took everything that’s wrong with eating in America, put it in a Vitamix, and shaped the result into a book, you'd get the Bulletproof Diet.

The book is filled with dubious claims based on little evidence or cherry picked studies that are taken out of context. The author, Dave Asprey, vilifies healthy foods and suggests part of the way to achieve a "pound a day" weight loss is to buy his expensive, "science-based" Bulletproof products.

But there's a silver lining: the Bulletproof Diet brings together in one place everything that should make you skeptical of fad diets. It's a teachable moment and its various offenses serve as a collection of giant, red warning flags.

"I have unlocked the single secret to weight loss!"


If that coffee isn't Bulletproof, you're in trouble. (Sean Gallup/Getty Images News)

Almost every fad diet-book starts with a compelling personal narrative. In this case, Asprey was a Silicon Valley investor who had all the personal success he could have dreamed of but not enough energy to enjoy it because, by his mid-20s, he weighed about 300 pounds.

So he channeled his nerdiness to "hack" weight loss, investing $300,000 of his money on research, travel, and experimentation. With this book, he’s bringing the secret of easy and quick weight loss to the masses.

Even without reading the book, you can be assured that however well-meaning the plan may be, it's bunk. I'm sure the diet worked great for Asprey, who looks very handsome on his book jacket. But every credible researcher I have ever spoken to on diet — notably those who aren’t selling books and products — has said that the one thing they have learned is: there is no one best diet that works for everyone.

A bunch of studies, and studies of those studies (or meta research), have shown that all diets — low fat, low carb, Weight Watchers, Atkins, etc. — have about the same modest results in the long run, no matter their macronutrient composition.

As I have written previously, these findings from the literature should be liberating: they mean that we’ve been sold this idea that if we just buy into one particular diet — and purchase all its associated books and energy bars and health shakes — we will walk the golden path to thinness. But science (and experience) have shown us that that's not true. The researchers all recommended simply cutting calories in a way you like and can sustain.

"You have to overhaul the way you eat completely!"

The researchers also warned, the more extreme a diet is, the more likely it is to fail. And make no mistake. The Bulletproof Diet is very extreme. It's basically a very low-carb Paleolithic diet that emphasizes saturated fat. 

To become Bulletproof — "reclaiming energy and focus" and "upgrading your life" — you need to cut your intake of gluten and sugar, stop eating grains and legumes, and nearly eliminate fruit because it's basically candy, according to Asprey.

As he told me, "The Bulletproof Diet is a roadmap not a prescription," but the roads he offers are so limited — and they begin with guzzling his brand of butter coffee each morning and then fasting — that it's hard to imagine how far one could reasonably stray and still get results. 

o one would quibble with the fact that we should all eat more vegetables and less sugar. After a science-y explanation of the evidence for the diet, Asprey rightly told me in an email, "There is no one on earth who can win an argument saying that white flour or soy isolate is better for you than steamed broccoli or a piece of salmon."

Most people know that, but can't live on diets that rely on these foods only, especially when they're based on expensive, branded versions of these foods (more on that later).

"The foods you and everyone you know eat regularly are toxic!"

california almonds

These almonds might kill you. (

In the Bulletproof Diet, Asprey ranks foods from "toxic" to "Bulletproof," claiming that his classification system is science-driven.

By this categorization, raw kale, raw spinach, pumpkin, hazelnuts, almonds, chickpeas, quinoa, and cantaloupe are "suspect." Corn, soy, and raisins are toxic.

I asked Asprey about this ranking system, and he explained that it's based on the "inflammatory" properties of each food.

To be clear, inflammation is real. You body mounts a localized inflammatory response in reaction to injury, and researchers are now trying to understand the role chronic inflammation plays in diseases like cancer.

But the nutrition researchers I spoke to — and other actual science-based thinkers — have pointed out that anti-inflammatory diets haven't been clinically validated. Now, some of these diets are very similar to the Mediterranean way of eating, which is linked with very good health outcomes. But to suggest that we know with certainty that specific foods reduce inflammation in people, and that has a specific health benefit, is far reaching at best and outright misleading at worst.

Still, Asprey went so far as to say: "There is one best way to help people lose weight, and that is eliminating inflammation." He said people who want to lose weight just need to test out different foods, determine if they cause them to  "feel food cravings and brain fog" and then eliminate those foods from their lives.

To find out about the evidence behind this system, I looked at a bunch of the citations for the claims that he makes about food. What I found was a patchwork of cherry-picked research and bad studies or articles that aren't relevant to humans. He selectively reported on studies that backed up his arguments, and ignored the science that contradicted them.

Many of the studies weren't done in humans but in rats and mice. Early studies on animals, especially on something as complex as nutrition, should never be extrapolated to humans. Asprey glorifies coconut oil and demonizes olive oil, ignoring the wealth of randomized trials (the highest quality of evidence) that have demonstrated olive oil is beneficial for health. Some of the research he cites was done on very specific sub-populations, such as diabetics, or on very small groups of people. These findings wouldn't be generalizable to the rest of us.

Another journalist, writing in the UK Telegraph, perused through some of Asprey's citations and was similarly unimpressed:

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.

Dr. Lydia Bazzano, director of the Center for Lifespan Epidemiology Research at Tulane University, wasn't surprised by the poor quality of the research he was using. There actually isn't a lot of good science in humans on the health impact of specific foods, she explained. This kind of research is extremely difficult to do. You'd need to get people to substitute particular foods in their diets, and study them before and after to learn about the effects of the dietary changes.

"But these studies are usually done on a short-term basis and have small sample sizes," she said. So they don't tell us much about the long-term effects of eating particular foods and, because they have small sample sizes, they don't always apply to the general population.

So you should be very skeptical when Asprey — or anyone else — claims to have found the "truth" about the harms of kale and nuts that others missed, especially when they are based on single studies. As Matt Fitzgerald, author of the book Diet Cults, summed up: "If a diet guru says that something you've eaten your whole life is toxic, change the channel — unless you're already dead."

"Stop eating an entire food group!"


Carbs really aren't the enemy. (Photo courtesy of Universal Images Group

While the Bulletproof coffee — a blended mixture of special Bulletproof-brand brew, butter and coconut oil — may be a novel gimmick, the idea that people should eat a low-carb diet is not new.

And it has failed time and again in the past because, again, most people can't live like this, said obesity physician Dr. Yoni Freedhoff. He points out, for example, that we tried restrictive, low-carb eating during the Atkins boom. "In the year 2000, it is estimated that one in five American households had one member who tried Atkins," he said. "If these diets were sustainable we would still see one in five families on it and we’d see improvements in the national waistline. We haven't seen that."

While it may be true that folks who go on low-carb diets lose a little more weight in the short run, it’s also true that these dieters have a very hard time adhering to them. "Any diet that takes things to the extreme can often help you lose weight in the short-term, but it is not sustainable," said Dr. Bazzano.

Asprey is right that the experiment of replacing fat with carbohydrates during the low-fat craze utterly backfired. Researchers now believe that we should get more fat into our diets than they did 20 years ago. But now Asprey seems to want to replace everything with fat. He swings the pendulum in the other direction, suggesting that up to 70 percent of one's calories come from this single macronutrient group. According to him, fat is the best kind of fuel, and our bodies need lots of it for optimal functioning.

Critics said Asprey goes too far with the fat claims. "Now we know if you’re getting almost all of your energy from any one of these macronutrients you need to think about whether any one of those diets are healthy and sustainable," said Dr. Bazzano, adding that
the recommended intake of fat based on the best-available research is about 25 to 35 percent a day.

Dr. Freedhoff agreed. "Ultimately the issue I have got with this style of diet — the issue with all low-carb diets — is not that they can’t work or help but for the majority of people who go on them, it’s not sustainable."

"The best way to lose weight is by buying my special products!"

grapefruit diet

Remember the grapefruit diet? That seemed like a much more innocent time in dieting fads. (Photo by Ulrich Baumgarten)

In Asprey's food categorizations, many of the items that rank as most healthy are his own branded products: Bulletproof Brain Octane, Bulletproof Chocolate Powder, Bulletproof Ghee, Bulletproof Whey, et cetera.

Alarm bells should go off any time someone claims that you should buy their expensive products for your diet. Especially when the products come with miracle promises, like Asprey's Unfair Advantage, which he suggests will help your body grow new mitochondria (the energy powerhouses of the cells).

Lisa Dierks, a dietician at the Mayo Clinic, said, "No matter what the diet is, when all of a sudden there are all these things you’re encouraged to buy to make the diet more successful, to me that’s always a flag."

She offered an alternative: "If a patient came into my office and said, 'I want to follow the Bulletproof Diet,' the first thing I would ask is 'What attracts you to the diet?'" Then she tries to figure out a more reasonable and sustainable approach, since, she said, she has seen highly-restrictive fads fail patient after patient.

She likes to remind her patients that what we know about healthy living is rather simple and very difficult for diet gurus to make money off of: eat mostly plants, do some exercise, don't smoke, and don't drink too much. These recommendations have survived study after study, and worked for generations of people all over the world. They're pretty much bulletproof.