Does the Keto Diet actually make athletes stronger or faster?
Does the Keto Diet actually make athletes stronger or faster? (Photo: happy_lark/iStock)

Sweat Science: The Keto Conundrum

Does the Keto Diet actually make athletes stronger or faster?

The ketogenic diet, a.k.a. “cutting carbs,” is all the rage in the fitness world. But is it better for you than any other kind of diet? And does it actually make athletes stronger or faster? These questions have been debated for hundreds of years, and every few decades the idea that cutting carbs can unlock your true athletic potential comes back into fashion. Canadian race walker Evan Dunfee was part of the most recent and most rigorous testing of the low-carb high-fat diet, which took him straight to the top of his sport. Just not for the reasons everyone expected.

Podcast Transcript

Editor’s Note: Transcriptions of episodes of the Outside Podcast are created with a mix of speech recognition software and human transcribers, and may contain some grammatical errors or slight deviations from the audio.




Outside Podcast Theme: From Outside Magazine and PRX, this is Sweat Science, stories of human endurance.

Peter Frick-Wright (host): In the beginning, there were carbs, and they were good.

Alex Hutchinson: It's just inextricably connected that if you want to enhance your endurance performance, you have to carbo load.

Frick-Wright: Runners run on carbohydrates. For the last half century, the menu for athletes has been pasta, bread, rice, and potatoes.

Hutchinson: It's like carbohydrates and endurance are the match made in heaven.

Frick-Wright: But then there was fat, and some said, it was better.

Hutchinson: In the sports world, it was in ultra running that people first started to say, Hey, I think it's better to just go on a low carb high fat diet.

Frick-Wright: The idea was that if you could tap into your body's nearly endless supply of fat, use it to fuel your workouts, you'd have basically an unlimited supply of energy. You could run forever. And then athletes started going out and doing it. In 2012, Timothy Olson broke the record at the Western States 100, a trail race in the Sierra Nevada mountains. Then in 2015, Zach Bitter beat the American record for a hundred miles running on a track and eating a diet almost completely free of carbs.

Hutchinson: It's just totally radically rejecting everything we thought we knew about sports nutrition.

Frick-Wright: This is Outside Sweat Science columnist Alex Hutchinson, and he was and still is covering the low carb high fat diet as it's surged in popularity. Now it's known as the bulletproof diet, paleo, caveman, Atkins, or the ketogenic diet. They're not exactly the same, but they all limit carbohydrates and reject the idea that carbs should be the foundational block of the food pyramid.

Hutchinson: So it becomes this sort of, the man versus the counterculture of --  they want you to believe that you need carbohydrates, but in reality you can set yourself free by following this new diet.

Frick-Wright: You've probably heard of at least one of these name brand diets, or have a friend who stopped doing carbs at some point. And for people with certain food sensitivities, dropping carbs can actually feel like a miracle cure. And in the weight loss world, this idea has been pretty popular since the two thousands, and because so many people are seeing such great results, there's a long standing debate about whether cutting carbs is the fastest way to lose weight and cash in on all sorts of internal health benefits.

Hutchinson: Or is that going to, you know, give you cancer and make your head fall off and do all sorts of other bad things.

Frick-Wright: What is new, and still very much up for debate, is whether or not a low carb, high fat diet is actually a superior nutrition plan for endurance athletes, or just an alternative.

Hutchinson: So then we've got this new layer that's not just is it good for you, but will it make you run a faster marathon or do better in your triathlon or whatever the endurance challenge that you're contemplating.

Frick-Wright: So today we've got the story of one man who was faced with an endurance challenge and was propelled to completely new heights thanks to a low carb, high fat diet, but maybe not quite in the way that proponents of the diet would like you to believe. That man is 28 year old Canadian Evan Dunfee.

Evan Dunfee: My name is Evan Dunfee.

Frick-Wright: The sport?

Dunfee: I'm a Canadian race walker.

Frick-Wright: Race walking.

(audio from race walking broadcast): But what we see you so often is a one or two walk is going out fairly fairly fast, but then they tend to drop back.

Frick-Wright: Evan Dunfee has dedicated two thirds of his life to the sport of racewalking, but he still has to explain what it is.

Dunfee: Everything is the exact same as running; the aerobic components that are necessary, all that stuff is the exact same as running. The only difference is that in race walking, we have to adhere to two rules: one foot always has to remain in contact with the ground; and your front leg has to be straight at the knee from the time it touches the ground until it passes onto your body.

Frick-Wright: If you can't picture it, imagine elite athletes trying to run but as politely as possible with their head back, perfect posture, arms pumping, hips on a swivel. And yes, it seems kind of weird artificially make yourself slower and still call it a race. But if you think about it, that's how swimming works too

Hutchinson: Race-walking is like that. It's like an out of the water version of swimming where form absolutely predominates everything. But you also have to be pushing to your physical limits.

Frick-Wright: So you can think of race walking as the breaststroke of track and field.

(to Dunfee) And how fast are you going? What's an Olympic speed for a race walker?

Dunfee: My personal best time for 50 kilometers is 3 hours and 41 minutes and 36 seconds. So roughly a 4 minute and 26 second kilometer.

Frick-Wright: For those of you unfamiliar with the metric system, that's fast.

Dunfee: It would be slightly quicker than a seven minute mile. For perspective, I know the marathon is something that a lot of people can relate to. So in 2017 I walked the BMO Vancouver marathon, and walked it in 3hours, 10 minutes and 32 seconds.

Frick-Wright: If you're not a runner or don't know marathon times, a three hour marathon puts you in the top 2% of everyone that runs marathons. You can qualify for Boston at three hours, five minutes. Evan nearly walked that. And the longer the race goes, the better he gets.

Dunfee: The 50 K is my primary event. I like the longer stuff. I wish there was an even longer event.

Frick-Wright:50 K is about 31 miles, so it's a quintessential test of endurance, a marathon plus a little bit, and Evans always sort of gravitated to the more drawn out athletic events. As a kid he struggled at stick and ball team sports. He was an average runner and only took up race walking when his older brother had his appendix removed. He couldn't take the impact of running. But Evan had a knack for low grade sustained effort. So pretty soon he was a really good racewalker. He set provincial records and then the Canadian under 18 record and then qualified for the Commonwealth games. Every year, he kept getting better, until it came time for the Olympics in London 2012 which is when he realized that when you start competing against the best in the world, he was kind of average -- middle to back of the pack. He didn't even make the Canadian team.

Dunfee: I guess more than anything, I just kind of lost sight of how much hard work it actually took and took for granted getting better and better and better. When I didn't improve for the first time was just kind of shocking more than anything else. And it was just sort of unexpected and it really rattled me. It took sort of that reaffirmation to be like, this is actually something I really want to do and it should be hard. If it's not hard, then it's not really worth doing. I think that that moment in London really helped solidify a bunch of those thoughts.

Frick-Wright: He set his sights on the 2016 Olympics in Rio de Janeiro, Brazil, which meant getting serious about his training, which in 2012 meant going to Canberra to train at the Australian Institute of Sport.

Dunfee: My teammate Inaki Gomez had gone down in 2011 and come back and was just like, this is amazing.It's three months of summer when it would be winter otherwise. So for that reason alone, it's great. The training environment, the people, the infrastructure there. It was just so new to us and something that we had never even really imagined existed.

Frick-Wright: He trained with the best race walkers in the world, including Jared Talent an Australian who’d two medals in London, and he worked with Louise Burke, head of Sports Nutrition at the Institute.

Dunfee: And so from there, I started going back pretty much when every opportunity I got. And then in the winter of 2015, Louise Burke and Jared got in touch and said, Hey look, we're doing this supernova thing, looking at the effects of a high fat diet. Would you want to come out and do it?

Frick-Wright: If you want to study how fuel affects endurance, race walking is an interesting sport to look at. And the reason why it has to do with how muscles can switch between types of fuels.

Hutchinson: So there are three macronutrients: protein, fat and carbohydrate. And when you're talking about endurance performance, protein, we can mostly ignore it. So it's either fat or carbohydrate, and there's been well over a century of research trying to figure out which fuel dominates, which is more important, how the body decides what to burn when.

Frick-Wright: In general, when you're doing easy exercise, like walking or on a light jog, you’re  burning fat. But as you speed up, the body starts drawing more and more from carbohydrates, which it turns into glucose. That's because before the muscles can actually use fatty acids or glucose, both have to be turned into something called adenosine triphosphate or ATP. You can think of fatty acids and glucose as different kinds of crude oil and ATP is like gasoline, the thing your engine actually runs on. You've got a virtually bottomless supply of fat, but the process of refining it to ATP is simply too slow to keep up with your muscles’ needs when you're really pushing hard -- you can make ATP from carbohydrates twice as quickly. That's why as the intensity of your workout increases, your body starts switching to carbohydrate.

Hutchinson: So you've got this variable fuel mix that goes from virtually all fat to virtually all carbohydrate depending on how intensely you're going.

Frick-Wright: The exact mix for any given effort depends on a bunch of things including what you eat. So if you eat more carbohydrates, your body gets better at burning carbohydrates.

Hutchinson: And the more fat you eat, the better your body gets at burning fat. This is well known, has been known for a long time, studies going back a century.

Frick-Wright: So sports scientists have known for a long time that at top speed, we’re mostly burning carbs. But then in the nineties researchers started looking at whether or not you could prime the body to burn fat more quickly by giving it only fat. The theory was that by denying your body carbohydrates in training, you could force it to rely more on fat. Then in a race, you wouldn't need to tap into your precious and limited supply of carbohydrates until the finishing sprint.

Hutchinson: From about, let's say 1995 to 2005, this was a huge area of research in sports science, but it just never produced the results that people expected. No one could demonstrate that it was actually better than the usual approach and around 2005 people finally figured out that if you eat a high fat diet, not only do you get way, way better at burning fat, you also get worse at burning carbohydrate. In fact, your body kind of throttles your ability to burn carbohydrate, and this is a problem if you're a competitive athlete because it means you've got no finishing kick.

Frick-Wright: In 2005, a definitive study at the University of Cape Town showed that cyclists were significantly worse at mid race sprints and surges after spending time on a high fat diet, even when using carbs for the actual tests. And for the most part that was that without carbs you didn't have any explosive power. So everyone pretty much decided that high fat diets aren't right for most athletes. But the thing is no one really told the athletes. They kept experimenting with cutting carbs and they seemed to like the results.

So even after having declared the 2005 cyclists study to be the nail in the coffin of high fat diets, Louise Burke at the Australian Institute of Sport started to look for ways to test it out again. And she thought maybe you could apply the diet to an activity where there was no sprinting. What if there were an endurance sport where a brisk walk was as fast as you ever went?

(audio from racewalking event): Dunfee, who’s been working so tremendously hard training in Switzerland -- he's been working with a psychologist and he's somebody who has a degree in kinesiology. So he knows about human physiology as well as anything else.

Frick-Wright: (to Dunfee) And what was your like nutrition game plan like before that -- had you ever heard of the high fat diet?

Dunfee: I had heard bits and pieces of it through my degree. My diet at that point, and probably still now, is one of those things that's probably in the like big things that could change for the better. Training 200 kilometers a week kind of provides me an opportunity to make the excuse that I can have more donuts. And so for me, going into supernova, it was a radical change cause I basically lived off of sugar.

Frick-Wright: The supernova experiments began in the fall of 2015. Evan joined 19 other elite race walkers in Australia and the plan was to divide them into two groups, restrict the carb intake of one of the groups for three weeks, and see if their bodies could adapt to run on fat. All their meals would be prepared for them and they would try to force their bodies to adapt, no matter how much it sucked.

Dunfee: It was awful. For those first couple of days-- that first time that I just had nothing to compare it to.

Frick-Wright: Physically, the workouts were grueling. Even the ones that were supposed to be easy. Evan's heart rate was higher, his times were slower and he felt terrible. But there have been several studies going back to the 1930s that have shown that with long enough to adapt, your body can run on fat. And Inuit cultures traditionally lived on what was essentially a low carb, high fat diet. But that doesn't mean it's easy to switch. Your body will do everything it can to convince you to take in more than the 40 grams of carbs Evan Dunfee got each day.

Dunfee: So 40 grams of carbs is nothing -- that's two medium sized bananas, I guess.

Frick-Wright: The first step of each training session was hard and Evan said it never got any easier.

Dunfee: My teammate Inaki Gomez, who's like this stoic, strong character,  after one of his long walks just ended up collapsing down beside one of the vans and just broke out into tears. And it was just inexplicable, like he didn't know why he was doing it. He couldn't understand why it was happening, but like it was just so emotionally draining trying to get through that training in those first couple of days, that first week.

Frick-Wright: Mentally, it was also grueling. The supernova study had both a high carb and a low carb group and they ate their meals right next to each other.

Dunfee: You sit down for your pasta dinner, which was zucchini pasta with a carbonara sauce. And you're looking at this bowl and your bowls a third full and instinctively you know that you're getting the same number of calories as the person next to you. But you look at the person next to you and they had this overflowing plate of pasta and bolonaise sauce and and even though, you know, it's the same number of calories, it just can't convince yourself of that. So you're watching these guys eat and you're just getting depressed and depression in the lightest sense of the word was an overarching feeling that a lot of guys had.

Frick-Wright: But over the next few weeks as they continue to work out and eat fat, their bodies did start to adapt. In fact, they basically became fat burning super ovens, torching it faster than any of the researchers expected. 1.57 grams per minute at the end of a time trial. That's like burning a half pound of fat every two and a half hours, and as they adapted, the workouts started to feel a little bit easier. Instead of being totally grueling, they were just hard and unlike a normal workout, they didn't get any harder at the end.

The reason for this has to do with how your body portions out energy. Carbohydrates are stored in your muscles as glycogen and you're carrying about 2,500 calories worth of glycogen around with you at any given moment. You also have another 400 to 500 in your liver, but that's getting into the weeds. Anyway, if you're running around burning through your glycogen, you start getting near the end of those calories, like at the end of a workout, your body starts to complain. It hoards resources, tells you you're done. Tries to convince you to stop and then finally you do, you bonk, because your body really doesn't want you to get to the end of your supply of energy. But when you're running on fat and you're used to turning it into fuel, it never feels like it's running out of gas because it's not.

Dunfee: In the overall, on the high fat diet, it was kinda just like moderately hard start to finish. Once you kind of accepted that and once you realized that it wasn't going to get harder at the end, you became a little bit more okay with it being hard at the beginning.

Frick-Wright: Did they get faster than when they were on carbs? No, they did not. And when you're watching someone else eat pasta, while you pick out a bowl of zucchini, not going any faster -- it's like adding insult to injury.

Dunfee: Nobody was sad to come off the diet. I think that's pretty telling.

Frick-Wright: What was it like to come off of the diet? How did it affect your performance and mood and everything?

Dunfee: Quite funny actually. So the last day of the study, I think I weighed in at 64.1 kilos.

Frick-Wright: If you're wondering 64 kilos is 141 pounds.

Dunfee: At the best of times I don't have great self control and I tend to indulge a little bit aggressively. And so coming off of three weeks of being told exactly what I had to eat, I definitely overcompensated. So that morning, 64.1 kilos; that night after free eating all afternoon had 70 kilos.

Frick-Wright: 70 kilos is 154 pounds, so that's 13 pounds he gained back in a day.

Dunfee: Definitely overdid it. Then the next morning had a 25 K walk to do and I crushed it and it felt great. It was almost immediately after coming off a diet, things felt normal again.

Frick-Wright: But would he be any faster? Yes. It turns out he would. Kind of. More after this break.


Frick-Wright: Okay, so before the break, Evan had just come off the low carb diet, gorged himself on carbs, gained back 13 pounds and now it was time to race walk. And here's where things get amazing. And stories like this are probably why the low carb, high fat diet has so many people that swear by it. Because despite all those studies in the 90s and early 2000s that showed you don't get a performance boost from coming back on the carbs after a strict low carb diet, it sure your feels like you do. And Evan went out 10 days later and walked 50 kilometers faster than he ever had.

Dunfee: I set a Canadian record, had a personal best by over five minutes and that came out of nowhere, I did not expect that at all. I didn't go into the race thinking that that was on the cards. So that was a pretty big like, Oh wow. Like what happened there?

Frick-Wright: All of a sudden he was fast, and throughout 2016, he stayed fast. By the time the Olympics rolled around, Evan was in contention for a medal.

Hutchinson: If you'd asked me in 2014 I would have said he's going to go to the Olympics and he's going to come, let's say 25th or something like that. Which is very impressive, I would slice off my right arm to come 25th at the Olympics. But I didn't expect him to be in the conversation for a medal. And that only became a realistic possibility in the months leading up to the Olympics.

Frick-Wright: And here, let's pause because what happened at the Olympics is not only dramatic and amazing, but it was also something of a test for this brand new Evan. He'd had his breakout performance after coming back on the carbs following three weeks on the low carb high fat diet. But the Olympics were nine months later -- any metabolic effects would be completely gone and he wasn't going to go low carb again in preparation. So was he turning his back on a secret weapon?

(audio from 2016 Rio Olympics): Well, hello and welcome to the Main 50 kilometer racewalking Rio 2016 Olympic game.

Dunfee: So the 50 K race in Rio was what I was working every day in 2016 towards -- that was my bread and butter. That's where I knew I was going to have a chance. And that's where I wanted to really fight for a medal. And I had never raced 50 K at a world championships or Olympic games where I was with the lead group. And so I wanted to get experience doing that. And so I just said, Hey, just stick with the leaders for as long as you possibly can.

(audio from 2016 Rio Olympics): It is a very competitive field indeed.

Dunfee: And so the race started and I put myself right there and I was feeling awesome. I was feeling great and I got carried away and I stupidly ended up walking off the front of the field and led the Olympic games, from about 25 K to about 39 K.

(audio from 2016 Rio Olympics): The race is on for gold, silver and bronze in this Olympic walk.

Dunfee: At 39 K I ended up having three of the guys come past me and was sitting in fourth place. Those top three guys pulled away a little bit and I kind of had this moment to sort of feeling sorry for myself. I was like, Oh, I know I'm in fourth place, that's pretty good. The guys ahead of me, they're too far ahead of me. I'm not going to catch them. The guys behind me, they're too far behind me, they're not gonna catch me. I'm probably gonna finish fourth and like, Hey, that's cool.

(audio from 2016 Rio Olympics): Reaching up towards the 40 kilometer mark now, Evan Dunfee still going on.

Dunfee: Obviously fourth place at the Olympics would have been a great result and I would've been ecstatic with it. But I think just in that moment I just kind of was tired and not thinking straight and kind of just sort of lost sight of what my goals were.

And then at 45 kilometers, uh, I was 18 seconds back of the third place athlete and I kinda just clicked back in. I had this moment where I was like, Hey, wait, no, no, no. You said your goal was to come here and to fight with those leaders and put yourself in a position to try to win a medal. And even if it meant you didn't finish the race, even if you collapsed at 49 K that was fine. But what are you doing sitting back here feeling sorry for yourself? Go catch those guys. You can do this.

(audio from 2016 Rio Olympics): The battle of the bronze is still going on.

Dunfee: I remember looking at my legs, like come on legs, just take one more step. And they did. And so I was like, just take one more step. And again, they did. And so I just said take one more step, take one more step, take one more step, and, 4,001 hard steps later, pulled up alongside Hirooki Arai ofJapan at 49 kilometers into the race. We're 3 hours and 37 minutes in -- we’re four and a half minutes from the finish line. We're both absolutely exhausted and we're fighting it out for the bronze metal. So I went to go past him. He ended up passing me back. And in the process of that we got a little bit too close to each other and he ended up just sort of bumping into my shoulder a little bit. And it was such incidental contact, was really, really nothing, but 3 hours and 38 minutes into a race, every little thing was magnified. And that little bump completely threw me off my stride and my knees buckle underneath me and my legs sort of started to give out and sights.

(audio from 2016 Rio Olympics): But he's struggling. Dunfee -- oh no.

Frick-Wright: After the bump, the race was pretty much over. Evan went on to finish fourth, and on the video, you can see his legs give out just moments after he crosses the finish line. He really had nothing left.

Dunfee: Collapsed at the finish line. Didn't have a single step left in me. I kind of left everything I possibly had on the race course and I was pretty happy with that. In that moment, when I crossed the finish line, I was pretty ecstatic. Had broken my national record again, had walked 3:41. After the race, about an hour and a half after the race, Hirooki, the athlete who’d finished third was disqualified. So I became the third place athlete because of that contact. He appealed two hours later. So I was the bronze medalist for about two hours, and then his appeal was finally accepted. So he was reinstated back into third place. I was, for lack of a better word, bumped back down to fourth place. We had the right of final appeal, so we could have appealed once more and said, no, that's the wrong decision, I think Hirooki should be disqualified, I deserved that medal. I watched the video, I went back to the village and got some food in me and had a little bit of time to think about it and knew as soon as I saw what happened and how incidental the contact was that he wasn't an athlete who deserved to have his medal taken away from him and that there was no way to know whether I would have beaten him anyways. And it just wasn't how I wanted to win a medal.

Frick-Wright: So despite coming in just a technicality away from the podium, Evan still broke his personal record in that race. He'd gone faster than the race following his low carb diet and he hadn't even gone low carb. But what if he had?

Dunfee: That was the big question cause a number of us who were on the diet ended up racing really well. So that was what we want to investigate with Supernova 2.

Frick-Wright: Supernova 2 took place in January 2017, and this time they did the same grueling low carb diet, but instead of cutting them loose when they started eating carbs again, researchers at the Australian Institute of Sport kept tracking their progress to see if there was some kind of metabolic aftereffect that only kicked in later.

Dunfee: What we saw was more or less that all that happened when we came off the diet was we went back to where we were before. So basically all that happened was that  the negative effects of the diet were undone, the second we came off the diet: there was no super compensation, there was no magic advantage that the diet gave us, we were just able to get rid of the negative stuff really quickly.

Frick-Wright: Even for racewalkers, perhaps the fat burningest Olympic sport out there, denying your body carbs and then giving them back again doesn't create any kind of Slingshot effect, make you faster, more efficient. But then how do you explain Evan's sudden improvement? Well, what depriving yourself of carbs does, according to Evan, is make you tougher.

Dunfee: It was three and a half weeks of just mental fortitude training. It was three and a half weeks of just grinding it out and getting through it and knowing that I could do it. I think that's what really I gained from the diet more so than any sort of physiological advantage that came from high fat. It was more of this like mental like, okay, I can do three and a half weeks of training and push hard every single day and just feel exhausted and feel tired and feel and have it feel awful and I can push through that and I can make it through that. That's sort of what I gained more than anything else out of the diet.

Frick-Wright: Instead of finishing a relatively comfortable eighth place, Evan realized he could probably finish an uncomfortable second, third, or fourth if he gave it everything. It trained his brain to be comfortable with being totally gassed. So now when it's time to race, he goes for it.

Dunfee: And as a result of that, I've blown up fairly magnificently at our last two world championships and gone from being in the lead pack at 38, 39, 40 K, to not knowing if I was going to finish the race at 45K.

Frick-Wright: Before the diet, Evan was racing at the edge of his mental limits. Now he's able to push all the way up against his actual physical limitations or at least get closer to them. And as we've seen over and over again in the series, the key to endurance is almost always a matter of tricking your brain and to not giving up, even when it's telling the body to shut down. And training hard without any carbs is one way to get tough, but that still leaves the question of whether the low carb high fat diet can be a superior source of fuel for endurance athletes. The science continues to say no, but there's still hundreds of athletes who say yes and that's hard to argue with.

Hutchinson: I think it depends who you ask. It depends on your beliefs. I think it's fair to say that it's a lot harder to get used to low carb than it is to get used to high carb. But you'd certainly find some people who would vehemently disagree and say that their life has been changed by low carb, high fat. They've felt great for the first time in their lives and if they accidentally eat a carb or eat more than a minuscule amount of carbs, it makes them feel horrible.

Frick-Wright: What it seems to do is work for some people better than others -- but when it works, those people get very attached.

Dunfee: It was amazing when I would tweet something positive about the diet that would just be latched onto by the high fat army. And when I tweeted something negative about it, it would be latched onto by the high carb army. And it was just people preaching to their echo chamber. And for me that was super interesting. I did a podcast; someone had asked me to come on their podcast and they'd seen one of my tweets about saying I had had a singular positive experience and I tweeted about the diet. And so he asked me to come on the podcast and he thought I was going to just talk to how great the diet was and how much it improved my performance. And I started talking and he quickly realized that that wasn't my opinion. I don't think that podcast ever ended up airing.

Frick-Wright: It's pretty human to think that something that works for you will work for everyone else. And sure, when we see a top athlete claim high fat as the best way, it's easy to buy into their theory. Their performance is proof, right? But after his experiences with supernova, Evan doesn't think all that many people are really doing the high fat diet.

Dunfee: I think a lot of people think they're doing a high fat diet and they're nowhere close.

Frick-Wright: It's really hard to stick to almost completely cutting out carbs. Evan thinks that most people who try it are failing at it.

Dunfee: I think in a lot of times what ends up happening is that whenever you adhere to any sort of diet, you start eating healthier.

Frick-Wright: If you eat healthier, you probably feel better. And when you're expecting some kind of radical shift in energy, it's really pretty easy to confuse those feelings with the benefits of burning fat.

Dunfee: It was just so crazy for me to see how polarized that debate got and I think what Louise and his colleagues are trying to really promote is this idea of metabolic flexibility --  of using all of these different dietary interventions at different points.

Frick-Wright: The next frontier is looking into whether it's possible to improve your body's ability to draw from both carbs and fat by denying it carbs periodically.

Dunfee: Doing a really hard workout and then not replenishing your carbs, going onto a high fat diet for the day, and then the next day doing a really hard workout to get some sort of adaptation out of your muscles.

Frick-Wright: The theory is that your body might adapt to be able to run well on both fuels and switch between them without too much trouble. The science isn't finished, but metabolic flexibility may be the next big thing for elite athletes. For most of the rest of us, however, it’s probably just another reminder to pay attention, to have a balanced nutrition plan, and  stick to it. So in the end there’s still carbs, and they're good, and there’s still fat -- is it better? Well, probably not, but it might be just as good and being able to say that, that's huge.

Hutchinson: We're coming to deeply ambivalent conclusion about whether low carb, high fat diets were the sort of magic behind Evan Dunfee. But I think it's important to understand what a radical radical change it is that we can be ambivalent about this because I know for me, five years ago, if you claimed to me that low carb, high fat diets could be the way to the route to an Olympic medal for an endurance athlete, I wouldn't have even considered it for a moment. I would have said that, look, don't waste my time, go back to 1870 where you belong. We understand a lot about metabolism and we know that carbohydrates are the way to go. If you pin me down right now and say, what's the best way for an Olympic athlete to prepare for the marathon? I would still say nothing has changed from my perspective, that carbs are the way to go. But I'm 100% open to the possibility or in fact, I think it's been demonstrated that you can run a very, very good marathon on a low carb, high fat diet. I don't necessarily think it's better, but it's a radical change to even acknowledge that there's some debate about whether it might be better, and that it's probably just as close to as good if for whatever reason you want to go that route.

Frick-Wright: So eat fat or don't. But remember the lesson here is that Evan Dunfee gained everything by cutting carbs, but not because he got some kind of metabolic advantage. The diet simply showed him what he was made of, gave him access to a part of himself that he didn't know existed. In the world of endurance, there're going to be more diets, more theories and placebos and cutting edge science that seems promising at first, and sure you can try them out and you boost your performance by a percent or two, but because of the way we're built, the way our minds and bodies work together, the quickest way to a Dunfee type gain isn't changing the way you eat. It's changing the way you think.



Frick-Wright: This episode was written and produced by me, Peter Frick-Wright with editing and music by Robbie Carver. It was brought to you by Bob's Red Mill. Go to if you want to win prizes in our monthly giveaway.

Special thanks to Alex Hutchinson who writes about Evan Dunfee and other aspects of the low carb high fat diet in his book Endure.

The Outside Podcast is a production of Outside Magazine and PRX. We’ll be back next week with a very special, very happy episode.

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Outside’s longstanding literary storytelling tradition comes to life in audio with features that will both entertain and inform listeners. We launched in March 2016 with our first series, Science of Survival, and have since expanded our show to offer a range of story formats, including reports from our correspondents in the field and interviews with the biggest figures in sports, adventure, and the outdoors.