Does Intermittent Fasting Work?

Breakfast, we’re told, is essential—a part of a healthy lifestyle that’s about as negotiable as breathing. Martin Berkhan, a Swedish personal trainer and blogger, not only skips breakfast but lunch as well. And he’s more ripped than you are.

    Photo: FuzzBones/Shutterstock

Before he breaks his daily fast, Martin Berkhan does some heavy lifting—simple stuff like squats, presses, pull-ups, dips, all with added weight. Power lifting in the fasted state, he believes, is key to directing the body’s hormonal currents in a way that optimizes an anabolic, or muscle-building state. Then he proceeds, basically, to pig out for the rest of the day.

When Berkhan entered the strength and conditioning scene, he told me via email, the prevailing diet dogma at the time was characterized by certain unbreakable rules, such as: “Always eat breakfast to kickstart metabolism and to keep your muscles from falling off. Always eat a small meal every two to three hours to stoke metabolism, prevent starvation mode and stave off catabolism.”

He went along with it for years, eating breakfast against his body’s desire. Eventually he began poring over scientific and medical literature, concluding the path he’d been following was, “simply put, complete and utter bullshit, with a complete lack of scientific support to justify the obsessive adherence to the make-believe rules of the practices it preached.”

The term “intermittent fasting” first appeared in the scientific literature in a 1946 paper, "Apparent Prolongation of the Life Span of Rats by Intermittent Fasting" (PDF). The study offered experimental evidence that intermittent fasting—wherein regular, short fasts are part of the eating pattern—might somehow prolong life. Since then, studies have demonstrated a positive effect of IF, as it’s often called, on several other health markers for cardiovascular health, cognitive function, glucose regulation, disease prevention, and neuronal health.

Back when Berkhan followed the six-meals-a-day dogma, fasting was something insane people who didn’t mind losing muscle mass did. Now he sees muscle building largely in terms of tilting the hormonal playing field the right way. In the early stages of a fast, growth hormone is naturally released. This is good for losing fat and gaining muscle. Berkhan believes this is a powerful window that opens before the dreaded muscle loss of starvation mode sets in, where the body is primed to make the most of exercise.

On his Leangains blog, Berkhan has laid out a template for a fasted training routine in which each 24-hour day is carved into an eight-hour feeding window and a 16-hour fasting window. A night owl by nature, Berkhan will often end his eating window late at night, and not eat again until the following afternoon.

His fast is broken with the biggest meal of the day, which consists, basically, of whatever the hell you want it to, and protein.

“I encourage a healthy diet, and certain common sense practices that serve a function. But I'm also miles away from having any rigid rules that I enforce on people. Hell, you're talking with someone who eats six-pound cheesecakes and doesn't mind a drink or two—or 10—or whatever you're offering.” He’s also not too stressed about a few calories of milk or sugar in your coffee. He’s generally not too concerned about avoiding foods, like processed carbohydrates or sugar. He told me that the paleo crowd, many of whom follow and like him, are mostly “nutters.”

I pressed Berkhan about a popular paleo goal, the metabolic state called ketosis, in which rapid weight-loss can occur. That, to him, is the real-life equivalent of the dreaded starvation mode that even small fasts were once associated with. At this point, our email exchange became awkward, and never fully recovered, though we had our moments. Berkhan is clearly something of a pioneer, perhaps a genius, but with the patience of a two-year-old and a Lebron-sized ego, a cocktail that clashed with the limitations in my understanding of human physiology and my preconceived notions about fasted training and intermittent fasting. I could feel his frustration building.

For my part, I was at once put off by his attitude but fascinated with his approach and impressed with his results. I’ve been following his 16/8 plan for months, with undeniable results. Following the schedule, for me, has been quite easy, because I, too, hate breakfast.

One of Berkhan’s posts last year explored a phenomena that many people, including some of his clients, complain about as they approach their weight goals (in other words, reasonably fit people). Between 30 minutes and two hours after breakfast, many are hungry again. Berkhan’s hypothesis is that because levels of the hormone cortisol are naturally high in the morning, this creates a physiological environment that doesn’t quite know what to do with breakfast.

He doesn’t go as far as to say that everyone should skip breakfast, but if you’re following his 16/8 plan it would take some dedication. You’d have to finish eating early in the evening the day before in order for the start of your feeding window to coincide with the breakfast hours.

While the long-term effects of fasted training are anabolic activity—i.e., muscle-building—Berkhan believes there is also a small amount of catabolic activity—muscle breakdown—that can happen while you’re actually training. This has led to the only exception he makes to a literal interpretation of fasted training: the consumption of 10 grams of branch-chain amino acids, in shake form, before the big pre-meal workout. This tweaking of his program was unveiled as part of his response to the 2009 paper “Increased p70s6k Phosphorylation During Intake of a Protein–Carbohydrate Drink Following Resistance Exercise in the Fasted State.”

This paper was exciting to Berkhan because it offered scientific credibility to his ideas on fasted training. What’s more, the study was on humans, rather than mice or lab-grown sections of muscle. Using an established marker for muscle growth— the activity known as phosphorylation of p70s6k—the study compared the physiology of people working in fasted and fed states. The fasted group had double the marker levels for muscle building as the fed group. After summarizing what the paper means in the lean gains context, Berkhan gives this directive:

For fasted sessions, ingest 10g branched chain amino acids (BCAA) shortly prior (five-15 minutes) to your training session. This does not count toward the eight-hour feeding window that I advocate post-workout; that starts with your post-workout meal. By ingesting BCAA pre-workout, we can sidestep the increased protein breakdown of fasted training while still reaping the benefits of the increased anabolic response as seen in this study. Not only that, BCAAs actually increase phosphorylation of p70s6k when ingested in the fasted state prior to training. So by training fasted, with BCAA intake prior to sessions, we get a double whammy of increased p70s6k phosphorylation that should create a very favorable environment for muscle growth in the post-workout period.

Before Berkhan quit emailing me back I asked him his favorite sources of BCAA. “Xtend and beef flank Steak,” he replied. The suggestion that flank steak might be a suitable substitute for a commercial powder as a source of concentrated BCAA piqued my interest. I wondered if flank was a particularly good source of BCAA, or just his favorite cut of beef. So I asked for clarification on why flank steak? As Martin often did, he answered without really answering. “Because it’s fucking awesome.”

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