The secret to a longer, healthier life? Game meat and a 4am start

And then, of course, there’s food. Kearns is the co-author, with his former athletics coach Mark Sisson, of Two Meals a Day. The book makes the case for an ancestrally-themed diet eaten within a framework of a two-meal day, the three meal-day being a relatively modern invention. 

In its quest to turn each reader into “a fat-burning beast”, the book provides strategies, recipes and intriguing detail, explaining that frequent movement increases one’s levels of brain-derived neurotrophic factor, a molecule important for learning and memory. 

Processed and carbohydrate-rich foods and drinks, meanwhile, flood your dopamine pathways and bind with opioid receptors to create that familiar feeling of being unable to put down the Pringles tube. 

Rather than Pringles, eat the foods our ancestors ate. “It’s a very short list,” says Kearns, who is a wiry 56-year-old. “Meat, fish, fowl, eggs, vegetables, fruits, nuts and seeds.”

And what do Kearns’s meals look like? In general, he says, his eating schedule is pretty flexible, but “the main go-to meals are anything with pasture-raised eggs, and I eat a lot of steak, and I’m trying to eat more and more animal organ meat, things like bone broth and liver, because these are the real nutritional superstars. Same with oily cold-water fish.”

Kearns considers himself fitter now than his triathlete days. Since then, he says: “I’ve kind of recalibrated my athletic goals toward events that are explosive and short duration in nature, because those are much more aligned with health and anti ageing than extreme endurance pursuits.”

“We’re obligated to take care of ourselves,” says Kearns. “One great way is to clean up that diet. I don’t care if you’re 62, 72, 77, you’re going to get an immediate impact and immediate boost in health. And you can reverse disease risk factors in as little as a few weeks of dietary intervention.”

Little is agreed on in nutrition, and many scientists and nutritionists question certain beliefs common in the paleo movement. Living as our ancestors did, though, even if it’s an approximation, is a matter of common sense.

The paleo world-view seems a useful and revealing heuristic through which to view human wellbeing, a topic about which much remains to be discovered. Our knowledge will continue to evolve, even as our genome remains the same.

My week of primal living