Diary of an intermittent faster

A nutrition coach shares his experiences with three popular IF methods.

As enthusiasm for juice cleanses wanes, getting lean via the straight-up calorie avoidance of intermittent fasting (IF) is gaining traction. Proponents of IF promise exciting results, like an uptick in fat-burning hormones, improved cognition, increased leanness and strength, and, of course, fast, sustained weight loss. Is it true?

We don’t really know yet. According to Experiments with Intermittent Fasting authors John Berardi and Krista Scott-Dixon (both Ph.D.s and cofounders of Precision Nutrition), science is still at least a couple years away from understanding the complete effects of IF on the human body, and close to a decade from knowing which method works best. But evidence is building in favor of the practice.

"Intermittent fasting can be helpful for in-shape people who want to really get lean without following conventional bodybuilding diets, or for anyone who needs to learn the difference between body hunger and mental hunger,” Berardi says. “But it’s not the end-all; people have been getting in awesome shape for decades without the use of intermittent fasting."

With more than a million downloads on Precision Nutrition’s IF guide alone, it’s clear that the methodology is developing a significant fan base. That said, fasting can be tough on the body—specifically the female body. “The female body defends itself vigorously against perceived nutritional deprivation,” Dixon says. Fasting regularly could cause damage to the metabolism, especially when combined with other stresses.

The key: To experiment mindfully, say the Precision Nutrition coaches. Try a one-day trial fast to see how you feel and figure out what works for you, ideally with guidance from an experienced nutrition coach. While we wait for the research, some intrepid scientists are experimenting on themselves, Berardi included. He tried out a few IF methods (back to back, in the following order) while maintaining his workout regimen to find out what would happen:

fast one day a week

Pros: Eight pounds lost over the course of eight weeks, 60 percent of which was fat; minimal “brain fog” often associated with dieting.

Cons: During the first few fasting days, he was irritable and distracted by the thought of food.

Upshot: While this method might not be measurably better than conventional dieting, Berardi did enjoy it more and found it easy to fit into his busy life.

fast two non-consecutive days a week (a variation of the 5:2 diet)

Pros: He lost another 10 pounds over just four weeks.

Cons: The weight came off too quickly, and he felt terrible.

Upshot: It’s not something Berardi would return to, especially while maintaining his intense fitness routine.

leangains (fast for 16 hours in every 24-hour period; exercise at the end of your fast, then eat your biggest meal of the day)

Pros: Though Berardi gained four pounds in one month, 100 percent of that was muscle.

Cons: He experienced not-so-pleasant mood fluctuations and lack of focus in the last few hours of each day’s fast.

Upshot: Not necessarily the best for weight loss; in fact, Berardi had to modify the method to contain fewer calories in order to lose weight on the program.