Dave Asprey, 43, is best known for his concoction Bulletproof Coffee, the go-to caffeine kick of Silicon Valley, Hollywood and David Beckham. A Guinness-dense combination of coffee, two tablespoons of butter and a product he markets called Brain Octane Oil, a triglyceride oil derived from coconut oil, the recipe was inspired by Tibetan yak-butter tea. Before becoming a “biohacker”, he made, lost and remade fortunes in tech startups. The Bulletproof empire now includes shops, online sales and a podcast; Asprey’s latest book, Head Strong, contains his theories on how to improve your brain function in two weeks.

You’ve spent $1m and 20 years “biohacking” yourself. What does that word mean?
Biohacking is the art and science of changing the environment around you or inside you so that you have full control of your own biology.

It’s interesting to hear it described as an art and science – many in the scientific establishment would regard you as quite out there…
Oh no, the stuff I do is very science-based. The primary function in the scientific method is that you make an observation, you form a hypothesis and you test the observation. My observation for Bulletproof Coffee came while I was in Tibet – namely, why do Tibetans have a blender hooked up to a car battery that they carry around on a yak in order to blend their yak-butter tea? It didn’t make any sense but they do it. And two, why do I feel amazing when I drink it?

The stuff I’m doing isn’t just like flip of a coin – it’s a hypothesis based on reading thousands of papers about biochemical pathways.

How does your background in Silicon Valley inform your approach?
Hackers are systems thinkers and in order to take control of another computer, you don’t have to know everything about it. You just have to know enough and apply the right techniques. And it is experimental and it is OK to try something and fail. There’s a lot of fear in medicine and there’s also a lot of, “Well, we’re only going to do one thing at a time…” It’s very, very slow-moving and I don’t want to move slowly. I’ve only got maybe 85, 90 years. My goal right now is 180 years, because I’m doing something about it now instead of waiting.

In Head Strong, you write that you started biohacking because you had “brain fog” and were overweight. So you wanted to improve your health?
More than improving my health, it was about having control of my own biology. When I started out, I thought I had a couple of problems. I had some brain fog, like I’d try and pay attention or remember things and I couldn’t. I got pretty concerned about it. Then [the doctor] told me I had a very high risk of stroke and heart attack before I was 30. And I said, “Well, fix me.” And it was the utter failure of that approach that made me decide I had to take control.

What approach did you originally take?
I worked out for 90 minutes a day, six days a week for 18 months in order to lose the 45kg of fat I was carrying. I cut my calories, I went on a low-fat diet, but it only made me tired and hungry. It was miserable. So it was the desperation of, “For God’s sake, none of this crap works” – that’s what really got me motivated.

What percentage of calories do you think should come from fat?
I think 50-70% of calories should come from very specific fats.

Most dietary guidelines recommend 20-35%, right?
They absolutely would; this is higher. If you’re eating the wrong fats or eating them with a lot of sugar, it doesn’t work. If it’s margarine and canola oil, you’re going to get one result and if it’s coconut oil and avocados, you’ll get a different result. But if someone ups their vegetable intake, they stop eating processed foods and they up their saturated fat intake, they generally have amazing results that fly in the face of what you would expect.

What “results”?
This isn’t a small sample any more. My first book, The Bulletproof Diet, has sold globally somewhere around half a million copies. People consumed 48m cups of Bulletproof Coffee last year. It’s a big thing, and on my book tour for Head Strong, in every single city, there were people coming up and saying, “Dave, I lost 40lb, 50lb…” So the sample here is so large and the online forums are so large that anytime someone says, “There’s no evidence for this,” I’m like, “What kind of evidence do you like?” Here are tens of thousands of people who have struggled for 20 years to lose weight and have lost it effortlessly in a rapid period of time that you say is impossible.

Is it true you give your kids half a shot of espresso in the morning?
Yeah, I give my kids an espresso cup full of Bulletproof Coffee, so 100ml. The reason for that is that I want them to have the butter and I want them specifically to have the Brain Octane Oil because it turns off their hunger too. Little kids are hungry all the time. My kids just go off and colour instead of asking for food all the time; it’s kind of relaxing.

In Head Strong, you warn against brain kryptonite. What is that?
Just like your cellphone has a battery in it, you have a battery. It’s distributed throughout your body – there’s quadrillion ancient bacteria, mitochondria, that are incorporated into our cells and they take food and oxygen and make energy for us to use to make our thoughts, to move our muscles and do everything we do. The efficiency of that system is something you can hack. Brain kryptonite is something like margarine or seed oils (canola, corn, vegetable oil) – they poison those ancient bacteria and make them work more slowly.

You’re a big fan of smart drugs. We don’t have much idea of their long-term impact – does that concern you?
It depends on the smart drug and I do my research on each drug before I use it, because they’re different. The most controversial drug I’ve used was something called Provigil or modafinil, and I’m pretty well known for this one, because I was maybe the first Silicon Valley guy to raise my hand and say, “I’m doping. I’m taking the limitless drug. I’ve been taking it every day for eight years and it saved my career.” I would not have my MBA from Wharton without smart drugs. They have been fundamental to me being who and where I am today. I’m really grateful for them.

How much exercise should we do?
Exercise is really important but excessive exercise is bad for brain function. That’s what I was doing in my 20s and what a lot of people do today. In Head Strong, I recommend that you walk at normal pace for 20 minutes every day. That’s it. Then, once a week, do something really, really hard for 15 minutes: interval sprints, or lift really heavy things until you can’t lift them any more. If you do that, those are two different pathways for growing new mitochondria, for causing the battery in the body to recharge itself.

Many experts would regard your methods as pseudoscience. How do you respond to that?
If you look at my Silicon Valley career, what I do is I disrupt things that are broken or don’t work. And there will always be people pushing back. So I welcome all the critics: all they need is to turn the book over and look at the quotes on the back from the most successful and well-respected brain doctors and anti-ageing doctors. So I guess we’re all crazy… Or we all look better than the overweight people following the 1970s, low-fat, eat-healthy-and-exercise crowd. Their stuff doesn’t work and they’re living evidence it doesn’t work. You show me a powerful, youthful, healthy-looking person who follows that kind of advice who’s criticising the Bulletproof Diet. You won’t find one.

• Head Strong is published by Harper Wave on 18 May (£18.99). To order a copy for £16.14 go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99