Hello! Welcome to Leg Day Observer, an exploratory look at fitness, the companion to GQ.com’s Snake America vintage column, and a home for all things Leg Day.
Ever squatted on an empty stomach? Or gone 16 hours, by choice, without eating? If you did and don’t have the flu, then you might be intermittent fasting.
IF, which is going without eating for longer than you might usually, was the most popular diet of 2019, likely due to its rare place in the overlap of the weight loss Venn Diagram: eat what you want, lose weight, and get healthier. However, its long-term effects aren’t known, and recent studies on its near-term effects are also conflicting. A 2020 fruit fly study suggests sticking with IF might yield adverse effects; while a 2018 study by the German Cancer Research Center says it’s not much different from other diets. A somewhat-contentious study released Monday in JAMA Internal Medicine is the most recent to offer critique, suggesting it doesn’t aid in weight loss.
The diet also has, like so many other things on the nutritional vanguard, a vague origin in powerlifting and strength sports. That origin helps explain IF’s limits and goals, and how it evolved past an athletic curiosity into a weight loss’ biggest “secret.”
IF might present as a new diet, but it isn’t. People have fasted regularly, often for religious reasons, for millennia — Ramadan’s month-long, day-long abstainment is the best example — and often to great benefit. But fasting has also become fashionable.
The past 30 years saw the rise of low-fat and high-fat diets, while the past decade saw Whole 30, Mediterranean, and Clean Eating become popular. The former had issues, while the latter comprises of sane approaches to maximizing food volume and satiety while cutting calories. But one of the most influential diet books published since 2000 sits on the other end of that continuum, and scarily makes its emphasis on not eating. Enter, fasting as a trend.
The book, appropriately titled The Karl Lagerfeld Diet, was written by the fashion luminary and then the creative director of Chanel, and published in 2003. It chronicles a weight loss odyssey — over 90 pounds in 13 months — spurred by a desire to fit into Hedi Slimane’s skinny suits. In the slim book, a man of appetites becomes an ascetic, subsisting on toast and an egg for breakfast, downing protein supplements, and throwing away his leftovers. Lagerfeld ran on about 1,200 calories a day, a serious deficit, and a diet that turns happy people miserable.
After he fit into the suits he wrote it all down; describing a gruesome way to get to Point B. “It has to be a sort of punishment,” he said in an interview, admitting its extreme restrictions. And while focusing on sustaining hunger for a body image goal can create serious issues down the line, all diets involve hunger; none are fun, all are variations of Lagerfeld’s punishment.
As Diet took over the fashion world, a different book was influencing athletics: 2005 saw a former short-track speed skater and strength coach named Lyle McDonald self-publish a PDF — the preferred mode, then and now, of delivery for athletic nutritional literature — that offered a similar immediate weight loss solution for athletes who needed to keep their muscle. Titled “The Rapid Fat Loss Handbook,” McDonald’s book expanded a short-term bodybuilding cut to a sustained, weeks-long crash diet that excluded nearly all calories that weren’t protein or fiber. The severe recipes in the back hammered the point home.
IF as a fashionable action in powerlifting came on its tail and grew out of McDonald’s work. It was popularized not as a PDF or hardcover volume but a series of posts in 2007 on the bodybuilding.com forum.
Opening a thread that would last a decade and expand past the board maximum, Martin Berkhan, a Swedish lifter and former model, explained how he eschewed nighttime shakes and pre-workout snacks and instead skipped meals for 16 hours a day. Doing so boosted his muscle and lifts, and helped him shed fat. He broke down his lifting routine to a skeptical audience, and shared tricks, like green tea, and got scientific, discussing things like insulin and ghrelin production.
That early aughts lifting environment was closer ideologically to the 1970s than to today, still hewing to bodybuilders’ seven evenly-spaced daily meals and traditional bulk and cut cycles. Berkhan detailed his discoveries in more depth on his blog, Lean Gains, his branding of IF. Fasting here didn’t invoke muscle loss, bad workouts, and fatigue, but progress.
There is an endless supply of lifters who roll the dice on things, and as they did that with IF, the knowledge grew. Protein could be consumed in chunks, not every three hours; branch-chained amino acids, a sort of calorie-free partial protein, became effective pre-workout shakes; refeeds — occasional big starchy dinners — became standard.
It was easier than the old way, where the spaced-out meals were hard to organize and never satisfied, and which didn’t offer a path to “recomp” — losing fat and gaining muscle at once — like IF did. Powerlifters were now drinking tea half the day like ascetics, and exercising and refueling the other half. The diet became a rite of passage, or at least a rumspringa for anyone who lifted seriously; all seemed like the holy grail.
It all seemed to match up to a wealth of scientific literature, some that predated the bodybuilding.com forum. A study conducted by Mark P. Mattson, then of the National Institute on Aging, on time-restricted eating, showed its anti-aging properties as early as 2003. A 2011 study singled out IF as a more effective diet for cancer patients than regular dieting protocols.
As IF spread past the barbell and scientific communities into the rest of society, it became easier to follow. Unconstrained by protein requirements or macros, the diet could be either minimalist or unhinged: a long-term Lagerfeld thing or a binge-purge muscle-gaining cycle. It's perhaps intuitive that it became popular: popular: In a post-breakfast age, time-restricted eating is easy, and gels with classic wisdom like “no snacks after 10.” Unlike keto or flexible dieting, you don't have to overthink the ingredients. And while Berkhan’s 16-hour fast, eight-hour window diet was complicated, with different calorie marks for different days of the week, and a strenuous workout plan, civilian IF was easy: You skip breakfast, have a late lunch, and don’t snack. The main effort was time.
The (potential) health effects of intermittent fasting
IF’s health benefits which had been an early selling point became even more important.
Berkhan, who had likely been reading Mattson’s studies, touted IF as a hormone modulator: the time spent away from food changes digestion for the better. Academic studies had been exploring those points. Fasting, Mattson tells me, could slow down the production of ghrelin, which stimulates appetite and promotes eating — that early-morning hunger going away — and of insulin, which absorbs glucose in the bloodstream and which can lead to fat storage. Over time, it also increases the production of leptin, the hormone that stimulates feeling full.
Then there’s ketosis, dieting’s holy grail: the digestive state in which fat is burned for energy. IF can prompt that. Another study showed that fasting mimics exercise, inhibiting cells’ mTOR pathways; the feeding period thereafter acts like rest — a workout-rest cycle, but for the digestive system.
It all results in a headline-shaping diet, one easy to stick with but which feels like a magic bullet: IF makes you shed fat and forget that you’re hungry, and it makes you feel full.
The problem with most diets is that they don’t work. Meanwhile, IF might work too well — though that new study on IF and weight loss may prove to be another turning point in the conversation.
And IF’s focus on fasting can create slides into bad eating habits. Decoupling it from a substantive protein requirement — a serious, satiating source of calories — leaves the door open for unhealthy food, or, worse, habits closer to Lagerfeld’s, which seems rough for things like bone density in the long run. On IF, overcoming hunger becomes an adaptation, and for half the day the enemy is food.
The diet, which I’ve more or less followed for a decade, can, at the worst times, descend into a game of broken telephone, where a small feeding window becomes its own cheat day. It can be mistranslated from giving a digestive system day off to starving and inhaling, a self-contained, repeatable binge and purge cycle with few consequences.
At its worst IF transposes the shame so many dieters have regarding food and hunger into uneven, extreme eating habits. That kind of gluttony is a part of strength sports; one early IF selling point was that it let you inhale cheesecakes while keeping your abs. When food is fuel and forbidden half the day, things like cheesecake can be transgressive.
Professor Mark Mattson delivers a TEDx Talk on "why fasting bolsters brain power."
As the studies mount, one wonders how much of the diet’s success is hormonal modulation and how much is habit and ease. A decrease in the ghrelin hormone might be why skipping breakfast is easy after a month, but it might be adaptation, and the full feeling that’s rare elsewhere could be in equal parts due to a leptin spike or to IF’s respectable, non-measured meals. Mattson tells me that “these cycles of fasting/eating, fasting/eating seem to optimize health,” and that practically, “people should know that they can adapt” to the diet.
That adaptability — Mattson says it takes a month before the hunger pains from a skipped meal go away — coincide with the period when the diet’s benefits, which include insulin sensitivity, better blood pressure, and a resting heart rate, are measurable. So it could be both.
That adaptability also might be due to IF’s lack of emphasis on food. Even relatively comfortable diets like macros counting and Whole 30 contain some post-meal hunger. The punishment Lagerfeld describes comes either all at once or a little at the time. It feels easier to skip a meal and a late-night snack than to be hungry three times a day, and not see any respectable meals on the horizon.
Like most diets, IF works best when coupled with exercise. Mattson prescribes both in interviews, and IF’s immediate selling points — visible abs, easy eating, a sort of relaxation — seem to get most quickly delivered when paired with the strenuous weight exercises that increase muscle mass and metabolism.
To lose weight, you have to eat less than you like, and it’s never fun. Lagerfeld’s book acknowledged this punishment and faced it, while IF contrasted it with an eating window that mimicked real life. A decade in, Berkhan’s name is rarely mentioned in academic studies, and like a powerlifting Gorbachev, the revolution he started moved past him, and evolved beyond his grasp. His profile is small outside his immediate world, but he does OK. He’s pivoted to Patreon, where he has hundreds of subscribers; his Leangains PDF, available on Amazon, is a seminal niche lifting text.
Most of the principles he espoused then stand up; it’s hard to overstate the diet’s ripple effect. Mattson’s studies, and countless others, are slowly helping us understand a time-worn, revolutionary diet better, and assess it in the long-term. But what really makes it different from the diets of the past is that we’re discussing sticking to a diet for a decade.