Tim Noakes

Among the benefits of traveling internationally is that it gives you a different perspective on your own country. For example, in 2015 I spent two weeks in Kenya conducting research for my book The Endurance Diet, and it was there that I came to fully appreciate how screwed up America’s relationship with food is.

As part of my research, I ate nothing but traditional Kenyan food at every meal, and I returned to the States two pounds later than I’d been when I left. The most fattening characteristic of any diet is how processed its constituent foods are, and the Kenyan diet is minimally processed. But that’s not the only reason I lost weight during my East African sojourn. The other reason is that there are no food commercials on Kenyan television. None. Not that I actually watched a lot of television while I was there, but the larger point is that food is not constantly shoved in people’s faces in Kenya as it is here. And it has an effect. By the end of my stay, I found myself thinking about food a lot less than I did back home.

I thought of this experience recently when, against my better judgment, I waded into an online debate about fasted workouts. My goal in doing so was to help the other parties recognize fasted workouts as the simple, straightforward practice they are, but this proved impossible, and I think it’s because America has a screwed-up relationship with food.

I was up against two separate factions in this debate, both of which viewed fasted workouts as extreme and radical, each in a different way. One faction regarded the practice of completing a workout on an empty stomach as a kind of torture—a gratuitous sufferfest ending in degrees of exhaustion never approached in regular workouts. This is absurd. A fit and well-nourished athlete who chooses to delay breakfast until after a workout is only minimally compromised by having their metabolic fuel tanks less than fully topped up. The science is rather abundant in this area. For example, in a 2012 study by Australian researchers, trained cyclists completed 60-minute time trials in fasted and non-fasted conditions, averaging 282 watts after a good breakfast and 273 watts on empty stomachs. That’s a 2.8 percent difference in performance.

In prolonged exercise bouts, the impact of skipping breakfast is greater but still far milder than some athletes seem to believe. A 1999 study by Tim Noakes and colleagues found that moderately trained subjects lasted an average of 136 minutes in a time-to-exhaustion cycling test at 70 percent of VO2max in the fed state compared to 109 minutes in the fasted state. That’s an 18 percent difference. In practical terms, this means you should feel no more fatigued at the end of a 14-mile fasted training run than you would be at the end of a 16.5-mile post-breakfast run. If you factor in the additional effect of withholding calories during the run, which fasted workouts require, the difference becomes somewhat greater, but even then it’s nowhere close to extreme.

Why, then, do some athletes regard fasted workouts as extreme? I think it’s because we are overfed as a society. In America, unlike Kenya, not only are our television screens filled with (junk) food advertisements, but these advertisements are carefully designed to brainwash us into being disposed to overeat, attaching positive associations to words like “crave” and “stuffed” and negative associations to “hunger” (and I’m talking about normal appetite, not chronic malnourishment). Consider Snickers’ “You’re not you when you’re hungry” ad campaign, which encourages viewers to keep a 2-ounce calorie bomb in their pocket wherever they go so they can cram it down their gullet the moment they feel the slightest hint of want in their tummies. We all like to think we’re immune to such mind-meddling, and we’re all wrong, and the fact that a certain faction of athletes finds it unimaginable to occasionally delay breakfast until after they’ve completed a workout proves it.

Another thing that Kenya has a lot less of than America does is disordered eating. Not all pockets of American society have high rates of eating disorders, but endurance sport is one pocket that does. Research has shown that people who struggle with disordered eating tend to have a history of trying popular diets (e.g., keto) and dietary practices (e.g., intermittent fasting). This is not to say that such diets and practices cause eating disorders; rather, it’s evidence that individuals who are predisposed to disordered eating tend to be attracted by such things.

Fasted workouts fit this mold. They are the type of practice that certain athletes are drawn to for the wrong reasons. Although I don’t know of any real cases, I can easily imagine that some athletes have overused or misused fasted workouts and subsequently developed eating disorders. Because this risk exists, a certain faction within the endurance sports community believes that fasted workouts should not be promoted. But to me this is like banning automobiles because some people drive while impaired. Depriving all athletes of the opportunity to benefit from this practice is unfair to the majority of athletes who are at low risk of developing an eating disorder and it is also not a legitimate solution to the problem of disordered eating within the athletic community.

As an endurance coach and writer, I’m focused on promoting fasted workouts responsibly. Although not inherently risky, fasted workouts are an advanced method that only makes sense for athletes who are already doing the basic things that yield bigger improvements in fitness, which include training at high volume, maintaining high diet quality, obeying the 80/20 rule of intensity balance, and eating enough throughout the day every day. Fasted workouts are meant to help athletes who’ve already realized 99 percent of their genetic potential through these and other fundamentals squeeze out that last 1 percent. For everyone else—including all youth athletes—they can wait, and for those who have any kind of history of disordered eating or any reason to believe they might be at risk for it, they can wait forever.

By way of closing, I would just like to mention that in Kenya, for cultural rather than scientific reasons, most runners do their first and hardest run of the day before breakfast every single day. Someone needs to tell them how radical and extreme this practice is so they can stop doing it and finally get good at running!

I am not an exercise scientist, but I do have a strong interest in the science of endurance exercise, and every once in a while I speculate on the kinds of questions exercise scientists like to explore experimentally. For example, back in 2004 I found myself wondering if training in a hot environment might improve endurance performance in a temperate environment, sort of like how training at high altitude improves endurance performance at low altitude. My curiosity led me to put the question to famed sports science researcher Tim Noakes, who, in his prompt and courteous reply, dismissed the idea as “too bizarre to consider.”

Six years later, sweet vindication came my way in the form of a study appearing in the Journal of Applied Physiology under the title “Heat acclimation improves exercise performance.”

Led by Santiago Lorenzo of the University of Oregon, the study involved 20 highly trained cyclists, who were asked to complete a performance test in temperate conditions on two occasions separated by 10 days. Between the tests, all 20 cyclists completed a prescribed training program, but 12 of them did it in a controlled, hot environment (100 degrees Fahrenheit) while the other eight performed their workouts in the same temperate conditions (55 degrees) as the performance tests. The 12 cyclists who underwent heat acclimatization improved their performance in the temperate performance test by a massive 7 percent, while the control group showed no improvement.

Lorenzo’s team attributed the performance-boosting effects of heat acclimatization on endurance performance in cool conditions to improved efficiency in heat dissipation and increased blood volume. They also found evidence that it caused some changes in muscle cell enzymes, which may have contributed to the effect as well.

Several subsequent studies have mined the same vein vein more deeply. The most recent study on heat training in endurance athletes, published in the European Journal of Applied Physiology, offers important guidance on how best to use this method in real-world settings. Led by Mark Waldron of Swansea University, the experiment aimed to track the time course of adaptations to heat training.

Twenty-two male cyclists were separated into experimental and control groups. Members of the experimental group cycled indoors at 100 degrees Fahrenheit while members of the control group did an equal amount of cycling at 68 degrees. Waldron’s team measured VO2max in both groups before the intervention, on days five and ten of the intervention, and on days one, two, three, four, five, and ten afterward.

The results are interesting. Both groups exhibited an initial decrease in VO2max during the 10-day training period that was followed by a rebound beyond baseline afterward. The peak increase was higher in the heat-training group, but not until four days after the last heat-training session, with some variation between individuals. VO2max then began to trend toward decline in this group, though the amount of decline that occurred between day four to day 10 post-acclimation did not reach statistical significance.

In a nutshell, these findings suggest that if you’re going to use heat training to increase your endurance performance, you need to time it to end about four days before you race. This means that your heat training is likely to overlap with your pre-race taper. Is this insane? It might sound so, but there’s a difference between sound and substance. While training in 100-degree heat might be uncomfortable, it’s not going to kill you, and which would you rather do: 10 days of heavy, peak training in 100-degree heat or 10 days of lighter, taper training?

That being said, I don’t recommend that you try heat training for the first time before an important race. Instead, test it out early in a training cycle to see how it affects you. It won’t be wasted even then, because if it works it will give your subsequent training a nice boost.

I can’t help but wonder if doing one hot workout every week or so throughout a training cycle might have similar benefits. Personally, I would find this approach easier to manage. Heat training could then be used in much the same way carb-fasted workouts are, and perhaps the two methods could even be combined to minimize the number of training days that need to be set aside as “special” sessions. Can I get a real exercise scientist to look into this?

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