Only in an era of abundance could an industry—a particular mindset, really—churn out innumerable fad diets promising to be the silver bullet that will finally (finally!) offer perfect health, weight loss, and inner radiance.

At the moment the top sellers in diet and nutrition on Amazon promise you “total health and food freedom,” warn against “hidden dangers in ‘healthy’ foods,” guarantee “fast metabolism,” and declare a “revolutionary diet” that, among other things, helps you “combat cancer.” That’s a tall order for something that, for most of human history, was so scarce and difficult to procure that securing enough to eat was itself considered a blessing.

This is not your ancestor’s diet. Yet it appears that we can turn to our forebears for an important piece of nutritive advice: fasting. In one of the most in-depth pieces I’ve come across on this topic, it seems intermittent fasting is helping many deal with metabolic and immune functions.

Lest you think this a sales pitch—I’ve found the silver bullet!—let’s start at the conclusion. University of Illinois nutrition professor Krista Varady studies alternate-day fasting for a living. She readily offers up the fact that intermittent fasting—taking varied breaks from eating, either on a daily schedule or on alternate days—is “probably another nutritional fad.” 

She has observed that every decade or so fads switch and rearrange. To declare fasting to be an end-all is ambitious; human psychology is generally not designed for the long-term. Novelty usurps integrity and discipline. That said, Varady concludes of fasting, 

I still think that it can really help people out, and I think people who are able to stick to it really reap a lot of metabolic benefits.

The article opens with a 1973 case of a man who survived for 382 days ingesting only “vitamin supplements, yeast, and noncaloric fluids,” in what has to be a hero to the Soylent movement. A.B., as he's known, dropped 276 pounds. More importantly he gained back only fifteen over the next five years—one criticism of most diets is that the weight returns. 

This is an extreme example, enough to garner a place in the Guinness Book of Records. What A.B. was doing, however, is an old trick once performed, albeit not so extremely, out of necessity. It wasn’t until widespread advancements in agriculture at about 10,000 BC—humans had been growing and harvesting for tens of thousands of years prior—allowed our ancestors to settle down and treat themselves to relatively consistent nutrition. Our dietary habits changed dramatically. 

The synopsis: our ancestors were accustomed to intermittent fasting. They might not have liked it, but their organs adapted, just as ours adapt to an overabundance of sugar- and carb-heavy foods by failing to work properly. Neuroscientist Mark Mattson relates our odd food rhythms to another cycle we’ve completely restructured. Thanks to electric lights our circadian rhythm is thrown off, which affects when and how we eat. He states, 

When there was darkness in the evening, of course people didn’t have much to do. . . . The light enables us to stay awake later in the night. And now we have plenty of food, so we tend to eat.

I practice intermittent fasting at various cycles. I found the 16:8 cycle—fast for sixteen hours, eat all of my day’s food during eight hours—challenging, as I teach (fitness and yoga classes) in the mornings and evenings and often work out before my first class. Interestingly, research, on mice at least, is showing that changing the feeding windows from 16:8, 15:9, or 12:12 “didn’t make that much of a difference.” That said, a fifteen-hour feeding window didn’t seem to have much benefit at all. 

What are the benefits? Besides a metabolic boost and weight loss, here is what the science says:

  • Liver. As insulin resistance decreases and sensitivity increases, the liver’s glycogen source dries up. Your body begins burning ketones as energy—hence, the ketogenic diet—which derives its fuel from visceral fat. 
  • Immune System. Fasting prunes away T cells; breaking the fast replenishes your store of hematopoietic stem cells, which are used to treat cancers and immune system disorders therapeutically. 
  • Heart. Blood lipid levels decrease. So does blood pressure. Some studies have shown a decrease in cholesterol as well, though cholesterol science has changed greatly in the last few years. 
  • Brain. Improved memory and learning in mice. Neurogenesis, the growth and development of neurons, increases. 
  • Cancer. Fasting has been shown to slow the development of breast cancer and melanoma in mice. 

For a deep dive into the studies read the full article on The Scientist. Of all the fads to take root in recent memory, this technique appears consistently reliable. Forget about your blood type. In fact, forget about all food for prolonged periods during the day. Then enjoy the window you’ve chosen to eat within. 

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Derek's next book, Whole Motion: Training Your Brain and Body For Optimal Health, will be published on 7/17 by Carrel/Skyhorse Publishing. He is based in Los Angeles. Stay in touch on Facebook and Twitter.