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'Human guinea pig' Tim Ferriss doesn't eat for 72 hours at a time -- and he says it gives him more energy and focus

Andrew ‘Drew’ KellyTim Ferriss has a strict fasting regimen.
  • Bestselling author and star podcast host Tim Ferriss undergoes a monthly three-day fast in addition to longer supervised fasts.
  • He said the habit makes him feel physically and mentally refreshed.
  • There is established research showing that intermittent fasting is proven to be effective for weight loss, and emerging research suggesting it can slow cell ageing.

With the publication of “The 4-Hour Body” in 2010, Tim Ferriss embraced his role as a self-proclaimed “human guinea pig.”

He took a long-held interest in athletic training and nutrition and put it through the lens of his hit book “The 4-Hour Workweek,” experimenting with different workout regimens and diets based on research and drawing his own conclusions.

This love of undertaking often extreme physical experiments has continued, and one of his latest interests has been intermittent fasting. Business Insider recently spoke with Ferriss about his latest book, “Tribe of Mentors,” and he explained why he undergoes a monthly three-day fast, with additional longer, supervised fasts.

Note that Ferriss was adamant that you shouldn’t try any aspects of his regimen without asking your doctor about it, and that even short fasts should not be done carelessly.

The benefits of fasting

People have been consciously fasting for thousands of years for spiritual discipline and, increasingly so over the last several years, fasting intermittently for perceived health benefits.

Ferriss is interested in the discipline of fasting, but is primarily focused on the latter aspect.

The latest research into the practice of controlled intermittent fasting concludes that it is a safe and effective method for weight loss (stress on “controlled”; it’s not recklessly starving oneself), and there are increasingly strong indicators that it boosts energy and delays ageing by accelerating cell regeneration.

The vast majority of promising research into fasting’s anti-ageing benefits is in its early stages and has so far just been with rats and chimpanzees – but that hasn’t stopped people like Ferriss from experimenting on himself, with the guidance of researchers like the University of South Florida’s Dr. Dominic D’Agostino.

D’Agostino specialises in studying ketosis, the process in which the liver secretes hormones called ketones to help break down fat as a fuel source when there is not enough blood glucose, the body’s primary energy source.

Ferriss wrote in his 2016 book “Tools of Titans” that he began intermittent fasting and a ketogenic diet to help alleviate the energy-draining symptoms of the Lyme disease he had contracted.

Ferriss’ fasting schedule

Ferriss’ monthly fast typically begins on Thursday night and ends on Sunday night. He breaks it down in detail in “Tools of Titans,” but it involves plenty of walking, ketone supplements, and a small amount of coconut oil put into tea to ensure that ketosis is accelerated.

He allows himself “non-caloric unsweetened beverages” like tea and black coffee during this period.

Ferriss uses a finger-prick to measure his blood glucose levels during this period, aiming for a safe level of ketosis. This is especially important in his occasional longer fasts.

As you can tell, Ferriss likes to take things to the extremes, but intermittent fasting can also just last 24 hours and yield benefits. His friend Jocko Willink, a former Navy SEAL commander who’s also an author and podcast host, has a monthly 24-hour fast that he adopted after perceiving the benefits of the practice while in the military.

Ferriss told us that since he began regularly inducing controlled ketosis, he’s “had some very very clear cognitive benefits,” including more energy and focus.

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