I've received some strange health-related emails over the years, but one of the real standouts came from a reader following a gut-busting version of Ori Hofmekler's The Warrior Diet. This lad wrote to me in a panic, concerned about the chest pains he was experiencing after eating. Worried that the poor guy might be experiencing heart problems, I asked him to describe his symptoms and his diet and lifestyle habits in more detail.
When his reply came through, it quickly became apparent what his problem was - and it had nothing to do with his heart.
This young lad had, unfortunately, embraced some rather questionable dietary theories from the forums and websites he was frequenting.
In this case, he'd succumbed to the belief there was something especially beneficial about eating, not comfortably-sized meals spaced throughout the day, but one big gut-busting extravaganza in the evening, a practice that comes under the umbrella of "intermittent fasting" (IF). Each night, this reader - I kid you not - was eating an astronomical 576g of fat and 6,454 calories for dinner!
In one single meal, he was forcing almost 2.5 kilograms of food into his besieged gut!
Just looking at those figures is enough to bring on indigestion.
Dietary dogma, just like religious and political dogma, has a powerful ability to convince seemingly 'normal' people of the most absurd beliefs. In this case, IF dogma had convinced this lad it was quite OK to eat absurdly large amounts of food in a single sitting.
This same individual, by the way, came onto my forum a while later and in a thread about post-workout nutrition asked if I had any concern for health, or was only preoccupied with looks and performance. What made him ask such a question? Was I telling people to hook themselves up to catheters after a workout and infuse themselves with truckloads of steroids and growth hormone?
Nope. I was discussing the benefits of post-exercise - shock, horror, gasp - carbohydrates! Yep, those evil carbs that have been shown in study after study to accelerate glycogen replenishment after intense exercise and are therefore of immense value to those who perform strenuous daily exercise.
No study has shown any negative effect from consuming post-workout carbohydrates. I'm not quite sure where this reader got the idea that post-workout carbs were dangerous - maybe it was the same brains trust that convinced him it was quite OK to cram two day's worth of food into a single meal.
That folks, is the power of bullshit. And when it comes to IF, there is plenty of bovine excrement being passed around, masquerading as scientific fact. I recently had occasion to view an ebook in which the author claimed IF would boost growth hormone, accelerate fat loss, increase muscle growth, improve insulin sensitivity, and cause world leaders to have a huge hugfest, throw away their nukes, and let the world live in eternal bliss.
OK, so he didn't really make the last claim ... or maybe I didn't read far enough.
No doubt I'm going to get a bunch of hate mail from IF fanatics, but for those of you who are being swayed by the hype and are considering this style of eating, I think it's important you first get the other side of the story. In this post, I'll discuss the abundant research being ignored by IF proponents. If after reading this you still want to begin or continue IF, hey, best of luck to you.
A Fad is Born
The IF craze started in earnest after the 2003 publication of The Warrior Diet by Ori Hofmekler. In his book, Hofmekler claimed that Roman soldiers and hunter-gatherers starved during the day and ate large meals in the evenings, and that we should do the same. I wasn’t on the battlefield with the Romans and therefore can’t comment on their diet, but given the eventual fate of the Roman Empire, blind emulation of their alleged habits may not necessarily be a smart thing. As for hunter-gatherers, I describe in Chapter 12 of The Fat Loss Bible the abundant evidence showing primitive peoples routinely consumed multiple meals per day.
The most common prescription for IF is to eat nothing during the day, with the exception of coffee and juices if one so desires, and then eat a very large meal in the evening. Some IF proponents, including Hofmekler, explicitly encourage one to “gorge” in this evening chowdown. To further amplify the assault on one’s digestive system, Hofmekler also recommends eating not just one, but up to 3 meals spaced an hour or so apart during the evening “feast”.
Another common manifestation of IF is every other day fasting, in which one eats normally for 24 hours, then forgoes food the following day, before repeating the sequence.
IF proponents routinely point to studies showing weight loss and improved markers of glycemic control, such as insulin sensitivity, in support of their dietary recommendations. But the reality is these improvements are not unique to IF regimens. In fact, IF regimens have not demonstrated any tangible benefits in humans that cannot be achieved with less restrictive dietary and exercise regimens.
They have, however, shown several disadvantages compared to regular meal patterns. Perhaps the most useful research comes from studies involving Ramadan fasting, the annual Muslim ritual in which solid food can only be consumed prior to sunrise, and after sunset. During Ramadan, a large dinner is customary, while those who wake early enough are permitted to eat what is usually a small meal. Thus, Ramadan fasting closely replicates the kind of pattern promoted by one-meal-per-day IF proponents (Hofmekler also cites Ramadan fasting in support of his regimen).
Ramadan and Athletic Performance
A large volume of research shows worsened athletic performance during the month of Ramadan. In one study, researchers from Senegal put 200- and 400-meters runners through two training sessions, one during Ramadan and the other during a normal non-fasting time of the year. The 200 meters runners performed a series of 150 meters sprints, while the 400 meters runners executed a series of 250 meter sprints. During Ramadan the performances of the athletes decreased significantly, a factor associated with "severe" hypoglycaemia (low blood sugar) prior to the workout. No such hypoglycaemia was observed in the non-fasting experiment[1].
At the University of Sydney, resistance trained Muslim men were tested on a stationary cycle at three 10-minute workloads (45, 60 and 75% VO2max). The tests were conducted the week before Ramadan, the end of the first week of Ramadan and the final week of Ramadan. While the non-fasting tests were completed without incident, during Ramadan four of the eight subjects could not complete the third 10-minute ride at 75% VO2max[2].
In 2004, Algerian researchers studied two professional soccer teams before, at the end and 2 weeks after Ramadan. Performance declined significantly for speed, agility, dribbling speed and endurance, and remained low after the conclusion of Ramadan. The players also reported an increased incidence of headaches, tiredness, and dizziness[3].
In a study with moderately trained Muslim runners, researchers examined the effect of Ramadan fasting on endurance[4]. The subjects ran for thirty minutes at 65% VO2max, then performed a 30-minute time trial in which they attempted to cover the greatest distance possible. This test was performed before, during and after the month of Ramadan. Blood glucose was lower at the start of the Ramadan testing session, and eight of the ten subjects covered shorter distances during the Ramadan trial. Mean time trial distance during Ramadan was decreased by 201 meters (5649 versus 5448 meters).
Two subjects (20%) further reported experiencing slight headaches and giddiness during the RAM trial, particularly during the last 10 min of the run, an observation supported by a separate study on 750 Muslim individuals in which 55% suffered increased incidence of headaches during Ramadan. The same study also found 34.3% of the subjects experienced behavioural disturbances, such as feeling tired and being unwilling to work[5]
Moroccan researchers examined ten healthy young subjects and found that mood and subjective daytime alertness were decreased during Ramadan fasting. Alertness at 11pm, however, increased – just the opposite of how our bodies are programmed to function. Heightened nighttime alertness and reduced daytime alertness suggests significant disruption to our natural circadian rhythms, the 24-hour sleep/wake cycle governed by sunrise and sunset[6]. Indeed, in a later study the researchers observed Ramadan fasting increased both daytime sleepiness in healthy young males[7].
In yet another Moroccan study, researchers examined 100 healthy volunteers during the month of Ramadan for two successive years (1994 and 1995). All subjects were male (mean age 32) and 51% were smokers. Irritability was assessed over a six-week period (before, four times during, and after the end of Ramadan). Irritability was significantly higher during Ramadan, increasing continuously and reaching a peak at the end of the month. The same pattern was seen with irritability and consumption of psychostimulants (coffee and tea). Irritability increased more in smokers than in nonsmokers[8].
Less research has been conducted to examine the effects of Ramadan fasting on short duration strength and power activities. A study conducted on fighter pilots found Ramdan fasting led to a 10-12% decrease in maximal isometric strength of the biceps. Muscular endurance at both 35% and 70% of maximal voluntary contraction were also reduced by the end of Ramadan (−28%, −22%, respectively)[9].
However, a study of ten elite male power athletes (2 wrestlers, 7 sprinters and 1 thrower) found no performance decrement in the Wingate anaerobic sprint test during Ramadan[10].
In elite judo athletes, 30-meter sprint, multistage shuttle run, standing jump, and counter-movement jump performance did not change during Ramadan. However, average power during a 30-second repeated jump test was slightly lower at the end of Ramadan, and there was an increase in total fatigue scores[11].
Intermittent Fasting: Fat Loss and Muscle Growth
Another totally unfounded claim made for IF is that it accelerates fat loss and increases muscle growth compared to isocaloric standard meal regimens. A study by researchers in Netherlands actually suggests the opposite.
In this study, all subjects spent two weeks on an IF regimen and another 2 weeks on a standard diet[12]. The IF protocol consisted of fasting every second day, starting at 10pm and ending at 6pm the following day. Caloric intake during both diet periods was identical as was the proportion of protein, fat and carbohydrate.
Body weight, body fat, and lean body mass after 2 weeks of IF did not differ significantly from that after the standard diet. There were no differences between IF and the standard diet in blood levels of glucose, insulin, cortisol, glucagon, adrenaline, noradrenaline or thyroid hormones. Neither were any differences in fatty acid or glucose oxidation after IF versus the standard diet.
However, resting energy expenditure, when measured first thing in the morning on any empty stomach, was significantly lower after IF. This drop in the resting metabolic rate could not be attributed to changes in the aforementioned glycemic and hormonal markers. The researchers speculated that while they did not find changes in thyroid status, their tests could not account for possible changes in intracellular differences in triiodothyronine (T3), the most metabolically active thyroid hormone. Previous research has shown levels of an enzyme that enables production of T3 within muscles (something that can only be observed via biopsy) decline significantly after 62 hours of fasting[13]. Whether IF can result in similar changes is unknown.
Nonetheless, the finding of decreased REE hardly supports claims for a special fat-burning effect of IF. As the researchers pointed out, "a decrease in REE may also increase body weight if isocaloric IF diets are consumed for longer periods and/or if physical activity is unaltered. Our study period has not been long enough to increase body weight."
The researchers also observed lower levels of an enzyme called mammalian target of rapamycine (mTOR) after IF. mTOR is a key element in cell growth and protein synthesis, and hence muscle hypertrophy. The researchers did not observe any change in lean mass among their subjects, but as they were quick to point out, the duration of the study may have been insufficient to produce measurable effects on muscle mass. Again, while the design of this study does not allow us to come to any firm conclusions, the decrease in mTOR hardly supports any claim for accelerated muscle growth as a result of IF.
Not So Sensitive After All
Much ado is made about the improvements in insulin sensitivity seen in some studies of alternate day fasting, but regular vigorous glycogen-depleting exercise produces even greater improvements in carbohydrate tolerance and insulin sensitivity. Vigorous exercise also has the added bonus of making you fitter and much more athletic in appearance.
Furthermore, any potential glycemic benefits stemming from IF may not extend to females.
Heilbronn et al tested men and women after three weeks of alternate day fasting and found that females cleared glucose less efficiently from their blood after alternate day fasting[14,15]. When given a 500-calorie test meal, their blood sugar levels remained higher for longer, whereas the males experienced no change. This would suggest that IF may actually worsen blood sugar control in women. The insulin response to the test meal remained unaffected by alternate day fasting in women but was reduced in men, suggesting improved insulin sensitivity in the latter but not the former.
Conclusion
Intermittent fasting ticks all the right boxes for a successful fad; it is novel, ‘different’, and has gimmick appeal. Because IF is a relatively new area of research and conclusive human results are sparse, the emerging findings are subject to much creative interpretation. Throw in a sprinkle of facts, a generous serving of speculation, and an even bigger helping of hyperbole, and you have the perfect recipe for a myth-driven fad. Whether IF eventually proves itself to deliver long-term health benefits remains to be seen, but the research thus far indicates it’s a dud for those looking to optimize their athletic prowess. On that basis, I recommend giving IF a miss.
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