The Science Behind the Mental Clarity Diet

Butter coffee, keto, intermittent fasting. Does eating to prevent brain fog actually work?

Andrew Zaleski
Published in
9 min readApr 10, 2019


Illustration: Johanna Walderdorff

AtAt the end of 2015, Geoffrey Woo was preparing to embark on his first experiment with radical intermittent fasting: a 60-hour stint, from Sunday night to Wednesday morning.

“At first I thought, is this even possible?” says Woo, co-founder of a San Francisco-based company called HVMN, which sells nootropic supplements the company says can “keep your brain sharp for the long term.”

“But I saw some of my co-workers doing it successfully, saying they were more clear and more productive.”

Woo didn’t begin fasting only for the reasons science tentatively recommends: to live longer or to lose weight. He was just as thin several years ago as he is today at age 30. What he was gunning for was a cognitive hack. “The plan was longevity and the cognitive benefit,” he says. Woo wanted to clear the “brain fog,” as it’s colloquially called, and optimize his mental agility.

“The first two times I tried to fast it was terrible. It was hard,” he says. “By the third time, it felt pretty refreshing. I felt pretty clear.”

Woo now cuts out all food for 24 hours once or twice a week. Every three months, he goes 36 to 72 hours without a meal. He justifies his cleanses based on several years of tracking his own blood sugar with a continuous glucose monitor he wears on his arm. While fasting, Woo says, his blood sugar remains steady throughout the day, instead of spiking and crashing after a big lunch.

As a Silicon Valley entrepreneur, Woo is perhaps the ideal guinea pig for this sort of diet experimentation. He’s part of an ever-growing movement of biohackers finagling with nutrition in service of the one part of our anatomy that no one ever sees: the brain.

Eating for brain energy and focus has become one of the central underpinnings of a series of diet trends growing in popularity. There’s intermittent fasting; the low-carb and high-fat ketogenic diet; the MIND diet, which combines the Mediterranean diet and the heart-healthy Dietary Approaches to Stop Hypertension (DASH) diet; and the Bulletproof Coffee diet, founded by biohacker Dave Asprey, which…