Nerd Lab: Touching on the Extraordinary Work of Dr. John Hawley

We dive into the work of Dr. John Hawley – he has produced many seminal studies and papers in exercise science since the 1990s. Today, we wilk look at a few of his key papers on carbohydrates and how we adapt.

FT EP 271 Nerd Lab

In the exercise science community, there are several key researchers who come up again and again. These figures have helped shape and define modern exercise science, as well as how athletes train. One researcher in particular has had a hand in almost every debate and development over the past three decades, and his name is Dr. John Hawley

To say that Dr. Hawley has been prolific would barely being doing him justice. Not only does he have a number of publications that most researchers can only dream of, but many of his papers are also considered to be the definitive reference on many topics. Dr. Hawley has shaped the debates on carbohydrates as fuel, high-fat verses low-fat diets, and high intensity interval training.  

But perhaps one of Dr. Hawley’s most unique contributions to exercise science has been his experience as a biochemist. Most exercise science research tests to see if a particular training intervention causes athletes to improve yet, they barely touch on what’s going on in the body.  

Some of Dr. Hawley’s most important papers take a fundamentally opposite approach. In those papers, he starts by diving deep into the molecular processes in our bodies that cause us to adapt – whether it’s improving our mitochondria or increasing the size of our muscles. Then, with an understanding of those molecular pathways, he proposes how training might influence those pathways.  

RELATED: Fast Talk Podcast 211: Does Strength Training Hurt or Help Endurance Sports Performance? with Dr. Bent Rønnestad 

Specifically, the paper, The Molecular Basis of Training Adaptations is perhaps the most thorough explanation of the biochemistry of training adaptations. While it’s too dense to summarize in a podcast, we explain the importance of the paper, and how it influenced many of the current theories on how to train, including a molecular explanation for why Polarized Training works well in athletes.  

Dr. Hawley is a strong proponent for endurance athletes consuming a high-carbohydrate diet. But, early in his career, much of his research was focused on how to increase the ability to use fat as fuel. In his 1998 paper, Strategies to Enhance Fat Utilization During Exercise, he addresses many of the popular approaches to increase fat oxidation and explains why most of these approaches don’t produce improvements.  

Finally, we fast forward to a 2017 paper that Dr Hawley himself called “the nail in the coffin” on low-carbohydrate diets. The study was titled Low Carbohydrate, High-Fat Diet Impairs Exercise Economy and Negates The Performance Benefit From Intensified Training in Elite Race Walkers. This paper addresses whether race walkers could perform well on a very low carbohydrate diet.  

RELATED: Fast Talk Podcast 46: Inside Ketogenic and High-Fat Diets, with Dr. Timothy Noakes 

So, get ready for some molecular pathway nerding-out and let’s make you fast! 

Episode Transcript

Introduction to Dr. Holly


The Fast Talk Team  00:04

For anyone familiar with exercise science research, there are several key individuals whose work is repeatedly discussed. These figures have shaped modern exercise science and how athletes train. John Hawley from Australia has been one of these individuals for over 30 years. Many of his papers are considered to be the definitive reference across a range of topics, including carbohydrate oxidation, high-fat versus low-fat diets and high intensity interval training. One of Dr. Hawley’s most valuable contributions to exercise science is his experience as a biochemist, which helps us understand why and how adaptations occur. He uses this knowledge to explain the process at work within our body. When the conclusion is unclear, he’s able to propose a mechanism that researchers can then focus on for future work. Today, we’re discussing three of Dr. Hawley’s papers. One of those papers, titled, “The Molecular Basis of Training Adaptations”, is an incredibly thorough explanation of the biochemistry of training adaptations. While it’s too dense to fully summarize in a podcast, we explain the importance of the paper and how it influenced many of the current theories of how to train, including why polarized training works well in athletes. Stepping away from biochemistry, Dr. Hawley is also a strong proponent of endurance athletes consuming a high carbohydrate diet, but early in his career, his research was focused on how to increase our ability to use fat as fuel. In his 1998 paper strategies to enhance fat utilization during exercise, he addresses many of the popular approaches to increase fat oxidation. Finally, we fast forward to 2017, a paper that Dr. Hawley authored along with Louise Burke and several others. This study is titled, “Low Carbohydrate High-Fat Diet Impairs Exercise Economy and Negates The Performance Benefit From Intensified Training in Elite Racewalkers” and the title says it all. While there are hundreds of other papers we could have chosen, we think you’ll find the three we selected interesting and helpful in your own knowledge. So, come along as we discuss a sports science legend, and let’s make you fast.

Intro to Today’s Episode

Trevor Connor  02:12

Well, welcome listeners to another episode. This is a, Rob what we call these, our seminal series?

Rob Pickels  02:19

Yeah, I think seminal works tell you the truth. What we’re trying to do is discuss researchers, we don’t have the researcher with us in the room, but discuss works that have really been formative, I think in the history of Exercise Science. Sometimes these are review papers. Two of which we’re covering today are great review papers, and some are primary research articles as well. So we’re really trying to bring the worthwhile research to the people.

Trevor Connor  02:47

So today, this is a big one we are talking about. Dr. John Hawley and I will tell you the probably the hardest part of getting ready for this episode, besides trying to remember all the terminology that he uses, was actually picking three papers because he has been absolutely prolific. He has been involved in endurance sports science since the 90s and some of the biggest topics and has written about all of them. So I’ll start by saying, we picked three, we could have picked 50. This is not a definitive review of Dr. John Hawley because we just don’t have the time to do that.

Rob Pickels  03:28

No, definitely the truth. It was really difficult to to settle and I think that Trevor and I, we had to like we were out there trading like baseball players for our fantasy team to make this one work.

Trevor Connor  03:40

As we were planning this episode, we actually talked about it more as Dr. John Hawley’s lab because he has worked with a lot of other very famous researchers. As a matter of fact, one of the top researchers in the science of sports nutrition is Dr. Louise Burke, who is his wife. So if we couldn’t find enough papers to cover Dr. John Hawley, we have an equally robust resume from Dr. Louise Burke.

Rob Pickels  04:07

Yeah, Trevor, there’s another big name too, that we’re talking about today and that’s Dr. Asker Juekendrup, who typically we would associate as being a carbohydrate guy, but today we’re kicking it old school with him and we’re gonna actually be talking about fat utilization, but Trevor, before we dive into it, is there anything else you wanted to cover?

The Unsung Work that Goes into the Background

Trevor Connor  04:25

Yeah, I think a really important thing to know about Dr. John Hawley, which is something that has always made me excited about reading his papers is the fact that at heart, he seems to be a biochemist, meaning what he loves to do is really dive into what’s going on. So for example, sometimes we’ll talk about glycolysis, which is how you break down glucose in order to produce energy. So, normally when we talked about in the show, we just talked about glycolysis, but there are six steps in glycolysis and there’s all these enzymes that we can name and all these different molecules at different stages in glycolysis, going from glucose down to where it becomes lactate or pyruvate. That’s what excites a biochemist, they look at all those steps and go, Hey, what’s going on and I think what’s been really amazing about Dr. John Hawley in a lot of his reviews and a lot of his papers, is he takes that biochemist approach, meaning a lot of researchers will say, I want to see what’s the impact of X intervals on an athlete. So they’ll bring em’ i, they’ll do the study and go, they did improve, they didn’t improve. They might in the discussion of the paper somewhere, bring up a little bit of here’s what we think’s going on in the muscle tissue. Here’s what we think is going on with the the energy sources, but they’re not going to cover it a lot. Dr. Hawley takes an almost opposite approach of saying, I’m going to dive into the biochemistry. I’m going to figure out what is producing those adaptations when you do those hard intervals, what molecule does that activate? What proteins does that cause your cells to start building and then how do those signal all the different adaptations and he’ll go through all those steps. All those different molecular pathways to figure out what’s going on and then after he’s identified and understands those pathways, he then says, Here’s my theory about how exercise impacts those pathways and then you go and do that research. So it’s a different approach, instead of doing the exercise studies first and then maybe trying to understand some what’s going on. He’s trying to understand the biochemistry and then saying, Here’s then understand that biochemistry how I think exercise impacts that.

Rob Pickels  06:39

Yeah, Trevor, I do think that that’s an interesting point and reading through, it’s amazing to read the background. The here’s the understanding that we have of the knowledge and here’s where the gap is. So that’s where we need to look or in the case of a review paper, to go back and look at some of those interventional studies that begin to fill in those holes of the theoretical analysis, but I think that’s a really smart way to go about it to actually take that step back and try to understand what is going on. I think it’s easy for a researcher to really want the, how do I say, almost more like the accolades like, Oh, my God, this training is the best training you can do to get better at cycling. Everybody wants to do research like that because then you get intervals named after you, but this is a little bit more of the unsung work that has to happen in the background, so that we can go back and reference it and I will say, for me, it’s referenced because biochemistry is not my strong suit. So it’s important for me to always be up on Dr. Hawley’s work so that I can fill in my knowledge gaps.

Trevor Connor  07:51

And Rob is still angry at me because the one paper I picked from Dr. John Hawley is probably his densest biochemistry paper of all of them, which I loved. Rob’s like you’re making me read this.

Rob Pickels  08:04

Yeah, a little bit.

Trevor Connor  08:05

Just to show that he has stayed true to form from beginning to end, two months ago, he published a new review called the molecular athlete.

Rob Pickels  08:13

And I haven’t read that one yet.

Trevor Connor  08:15

Nope, nor have I but I’m excited to read it. I only discovered it two days ago.

Rob Pickels  08:19

Let’s get it on the list.

The Fast Talk Team  08:21

There are more female athletes and endurance sports than ever before. Yet, until recently, female athletes simply follow the advice and protocols that have been designed and tested on men. This is now rapidly changing and there are a host of experts bringing light to the perils and pitfalls associated with female athletes falling guidelines that are male specific. Check out our latest craft of coaching module, “coaching female athletes for expert guidance on coaching women”.

Trevor Connor  08:50

So Rob, where do we want to start?

Rob Pickels  08:51

Let’s talk about fat, Trevor.

Trevor Connor  08:52

Okay, I have a lot more of it than I normally do.

Rob Pickels  08:56

I think I have more of it than you do, unfortunately. So the question is, are there strategies to enhance fat utilization during exercise?

Trevor Connor  09:04

Not a not a simple question. Answer is yes, but according to this first paper, we’re going to talk about a lot of these tricks that we think help, might not make that big a difference.

How to Enhance Fat Utilization in a Workout

Rob Pickels  09:17

Yeah. So let’s see this is we’re going to kick this off with a 1998 study that is titled In fact ‘strategies to enhance fat utilization during exercise’ and this is a paper that Dr. Hawley teamed up with Dr. Asker Juekendrup and also Fred Bronze and they they studied, well first off because it’s Dr. Hawley, he started with explaining factors limiting fatty acid uptake in muscle cells, limiting fatty acid oxidation. He goes through all of the biochemistry before moving on to the techniques and they discuss a lot of different techniques here. Edurance training, caffeine ingestion, L carnitine, a popular supplement people take. Medium chain triglyceride, long chain triglyceride. Just straight up infusing fat into somebody’s veins, fasting and then also diet alteration, both short term and long term exposure to high fat diets.

Trevor Connor  10:16

As you said, he started out covering a lot of the biochemistry and I won’t lie to you that was part of the paper that I really enjoyed. As you said, goes back to 1998, but there was a lot in there that you still read and go, Oh, I had forgotten that or I didn’t know that and there’s some nice depth to it and one of the things that he reminded least me of in the paper is the fact that effectively, our fat stores are unlimited. Even a marathon runner has enough stored fat to keep a marathon pace going for days and days and days. They’re not going to ever run out of fat, but the issue that the first few pages talked about is the fact that fats don’t like being in water. They’re they’re hydrophobic. So actually transporting those fats from the Dipa sites, from your fat cells to the muscle cells and getting into the mitochondria, where it can be used is actually quite difficult and he goes through all the steps. How it has to be bound to albumin until it gets to the capillaries close to the muscles and then how it goes from the capillaries into the muscles and then inside the muscles, how it gets into the mitochondria and it’s actually quite a difficult process. So even though we have this unlimited fuel source that weighs less than glucose, for the amount of energy it produces, it’s hard to use it at a high rate.

Rob Pickels  11:43

Yeah, I think that’s an interesting fact in this is they start out by saying all the reasons they want to be able to upregulate the use of fat and how it makes sense that we really should be pushing this over carbohydrate for endurance, at least for endurance exercise performance and Trevor, I think it is interesting that you bring up the, not only that we have so much of it, but that it’s technically lighter per unit of energy than when we look at glycogen and other carbohydrate stores, but but you’re entirely right, there are so many steps in this process that are potentially rate limiting, that it just doesn’t seem to work out in the way that people would like it to.

Trevor Connor  12:27

So what it basically comes down to is we can go forever on fat, we just can’t go fast.

Rob Pickels  12:35

That is true, but when we are looking to increase our fat oxidation, maybe let’s start picking some of these apart. The first one that they tackle is endurance training and I’ll say out of all of the potential ways that we’re increasing fat utilization, endurance training seems to be the one that actually makes sense and actually has sustainable worthwhile improvements, both in performance and fat oxidation.

Trevor Connor  13:05

I will take it a step further and say there have been plenty of studies since then they’ve said, one of the most important adaptations in our body is learning how to use fat at higher intensities and sparing glucose. That is one of the biggest difference you are going to see between an elite endurance athlete and a an amateur athlete. So let’s say you take a brand new cyclist and an Olympic cyclist and you have them ride at 300 watts. They can both produce 300 Watts, but the the elite athlete is doing it all burning fat. So they’re just not really fatiguing. Where that that amateur athlete is relying mostly on glucose. They’re producing lactate, they’re just not going to last that long before the body says yep, enough. I can’t keep doing this.

Rob Pickels  13:55

Yeah, an interesting thing that we did when I was working in Dr. Indigo San Milan’s lab was we collected both fingerprick for me, ear prick for him, we differed on that, but we collected capillary blood lactate samples and we also did gas exchange to look at carbohydrate and fat oxidation during exercise and if you overlay those two graphs, the blood lactate and the fat oxidation, they are opposite each other. In the beginning of exercise, presumably when the athlete is going easy. The aerobic system is doing the majority of the work, then your fat oxidation is relatively high. Now it depends on the athlete and the lactate in the blood is relatively low and it’s amazing how those two change in lockstep with each other. The first stage that lactate increases above baseline is oftentimes the first stage that fat oxidation really begins to drop off and these are two distinct measures. They have nothing to do with each other. We’re pulling one from the breath and one from the blood and we know that, hey, we use lactate all the time as a measure of fitness in an individual, well, hey, that’s tied to that fat oxidation as well. So we know what these more fit individuals who keep their lactate levels low, as they’re working it harder and harder workloads, their fat oxidation is also going to be high at those higher and higher workloads and you’re right, it’s the hallmark of cyclists or runners or any athlete improving their endurance performance.

Trevor Connor  15:30

Something interesting that he pointed out in this paper that I had completely forgotten is when you are producing lactate, lactate will actually inhibit fat oxidation. So it’s kind of a vicious circle. If you’re having a hard time relying on fat for fuel and you start relying on glucose, you’re going to produce that lactate and then the lactate is going to signal back and say, stop burning less fat start burning more glucose and you’ll just have more and more towards relying on glucose for fuel, which is great, except it’s limited. You’re just not going to last that long.

Different Ways to Increase Fat Oxidation

Rob Pickels  16:00

Yep. I think that something to play off of what you’re saying. If we move on away from the endurance and onto the caffeine ingestion. There’s something that’s really interesting is caffeine is oftentimes thought to upregulate fat oxidation because of an increased level of lipolysis breaking down the fat, but and I know this for myself from taking serial lactate measures throughout the day, caffeine increases my blood lactate and we know that that blood lactate increase is going to reduce the fat oxidation that we have because caffeine also increases the amount of liver glycogen breakdown that we have. So caffeine, which we oftentimes think is going to enhance your fat burning ability in practice oftentimes has really no measurable improvement and not in anything that’s substantially worthwhile to tell you the truth over not having caffeine.

Trevor Connor  16:58

Well, I found it really interesting in the paper that he went through all these tricks that people were using at the time to increase fat oxidation. So he discovered one which was caffeine. He talked about L carnitine. supplementation, he talked about consuming medium chain triglycerides, he talked about infusing literally infusing fat into your blood, which we’ll get to in a second and except for that last one, he basically showed Yeah, there just doesn’t appear to be any benefits, doesn’t improve performance, doesn’t increase your time to fatigue, with the exception of infusing fat, which did seem to put in us in quotes, ‘spare glycogen’, the mechanism is actually different, but in the end it results in sparing glycogen, but pointed out who’s going to sit there on the start line and intravenously inject fat into their system.

Rob Pickels  17:48

Yeah, if I have an IV bag, I’m gonna have something else in it other than a fatty acids.

Trevor Connor  17:52

So it was interesting just to see them say, Yeah, doing a lot of endurance training is going to cause that shift and allow you to rely on fats a lot more at higher intensities. All these other things, not so much.

Rob Pickels  18:05

Yeah, and this is an area where I really appreciate his diving into the biochemistry because if we take L carnitine, he points out the primary function of L carnitine is transferring long chain fatty acids across the mitochondrial membrane. Perfect. If we have more carnitine, then we’ll move more into the mitochondria, but what happens in practice is you take that carnitine and it might go up in your blood a bit, but for some reason, that doesn’t seem like it makes it into your muscle cells and so the carnitine that you’re ingesting ultimately isn’t making it to the mitochondria. It’s not helping to increase that fatty acid transport and it’s really not changing your ability to oxidize fat.

Trevor Connor  18:48

I think that goes back to a term that I don’t know, I keep forcing myself to try to mispronounce this, but the Symmorphosis, did I get that right?

Rob Pickels  18:58

Maybe I’ll go with it.

Trevor Connor  18:59

It’s that concept that these processes in our body they’re all designed to be at the same level. So we talked about that in terms of of oxygen consumption, no step in the from when you breathe into your lungs, diffusing the the oxygen to the blood to the blood taking it to the muscles to the muscles uptake in the oxygen. They all develop at kind of equal level so that no one is overbuilt because if one step is over built, it’s pointless. The other steps are gonna be the rate limiters. So I think this is the same thing as we said, he went through the biochemistry at the beginning of all the steps it takes to get these fats from the adipocytes into the mitochondria and if you take L carnitine, that just up regulates one of those steps, doesn’t really matter because all the other steps are still gonna be rate limiting.

Rob Pickels  19:10

Now, whatever. There was a few things in this paper that definitely increased fat oxidation, but did not improve performance and one of those was fasting. So purposefully manipulating your glycogen stores so that you’re under fueled and you don’t have the carbohydrate in your body, that will 100% Increase the amount of fat that you’re burning during exercise, but you put that person in a performance or training situation and they can’t perform.

Trevor Connor  20:20

So interesting that this paper came out 98 because I remember when I was up at the the center in Canada, not too long after this. There was a ride there called, I think it was the coffee ride and the idea behind this and I think it was based on some of the concepts this paper is addressing is, you’d go out and do a six hour ride, but before the six hour ride, all you would do is have a cup of coffee.

Rob Pickels  20:46

Hopefully, we’ll have black coffee.

Trevor Connor  20:47

Yeah, yeah, that’d be it and it goes back to the idea, well caffeine is going to increase your fat burning, fasting increases your fat burning. So go out and do a six hour ride with no food, but all these things are going to upregulate your fat burning and you’re gonna burn a ton of fat and boy, it’s gonna be really good for you.

Stress Hormone Response to Low Carbohydrate Training

Rob Pickels  21:04

Yeah, if only it worked out that way. Something to point out is stress hormone response is way elevated in situations like this, when you’re doing this, this training on a low carbohydrate situation and it is really rough on your body and you can go back we have a few episodes, we can put them in the show notes about carbohydrate manipulation to try to say, up regulate PGC one Alpha through methods like this. It’s a very touchy, very difficult balance to get that right and there’s a lot of very well known individuals who are completely anti training in this fasted state.

Trevor Connor  21:40

I’m one of them, the coffee ride I bring it up, but not as a suggestion, but as a warning and I think this paper was probably one of the first things to kind of point this out and say, these sorts of tactics just aren’t the best idea.

Rob Pickels  21:54

Yeah. They also bring up something that’s kind of same, same, but different. Instead of just fasting, what if we eliminate carbohydrate from our diet and we have 80% of our calories are coming from fat and then a few percent from protein and essentially nothing from carbohydrate and again in this situation, essentially we measure your gas exchange through a metabolic cart and yeah, you’re burning more fat, but again, performance does not improve. If anything, performance gets worse and adaptations they’re not worthwhile in this in this situation.

Trevor Connor  22:33

Though, I think the one important differentiator to point out here is they looked at short term exposure to high fat diets. So just a couple of days versus long term exposures are more than seven days and they basically showed short term exposure, you’re just going to suffer from that. Long term exposure, there are adaptations. Now, as you pointed out, they said so far there’s no evidence of those adaptations improve performance, but there are definitely adaptations, you start relying more on fat for fuel and one of the things I noticed in some of those studies was, even though glycogen levels were decreased, it didn’t seem to impact time to exhaustion. It didn’t seem to impact how long you could rely on glycogen stores, as I remember.

Rob Pickels  23:18

Yeah, I think that that’s potentially true, depending on the workload that you are utilizing for these time to exhaustion studies and there are some situations where the rider is may be able to perform as well as they did before and there are probably other situations where they have a decrement in their performance, but we’re going to cover that in the next study.

Trevor Connor  23:38

Yep. So so we shift over there.

Rob Pickels  23:40

We certainly can, Trevor. You want to talk about racewalkers?

Trevor Connor  23:43

Yeah and I think we need to give a little historical context here and we might get ourselves in a little bit of trouble, but that paper we just talked about was written in 98, but for many years or several years before that Dr. Hawley was really focusing on this, can we up regulate reliance on fat. He felt that’s going to be one of the big ways to really help endurance athletes and it is worth pointing out that he did a lot of that research with Dr. Timothy Noakes and Dr. Noakes is now really known as one of the grandfather’s of the keto diet and he’s a big proponent of athletes should be keto, they should be high fat, very low carbohydrate. So it was interesting to see them do that initial research together and then ultimately, Dr. Hawley wrote this 98 paper with Dr. Juekendrup and said, You know what, there just isn’t any evidence and you saw Dr. Noakes go in a different direction. I think what we’re about to talk about these papers, this paper which was written in 2017 is and I actually spoke with Dr. Hawley around the time that he wrote this paper. He really said this is the nail in the coffin. That athletes endurance athletes need a high carbohydrate diet, but there’s just no way around it.

The Balance between Low and High Carbohydrate Diets

Rob Pickels  25:01

Yeah, without question. So this paper is called ‘a low carbohydrate high fat diet impairs exercise economy and negates the performance benefit of intensified training in elite race walkers’.

Trevor Connor  25:14

So where do we want to start here, besides the fact that he pointed out they had many very grouchy racewalkers?

Rob Pickels  25:21

They sure did. I think it’s interesting again that they start with this openness of, hey, we see all these benefits as to why we want people to be oxidizing fat and I think that that’s good, because oftentimes, researchers can go into something really biased and studies can be designed to ultimately lead to one outcome or eight. I mean, that’s just poor research design, but it does happen. So something that was interesting for this was, they actually had three different diets. They had a high carbohydrate diet, they had a high fat diet and then they had kind of a periodized carbohydrate diet, where if I remember correctly, it was ultimately over the course of time, it was the same amount of carbohydrate as the high carb diet, but depending on their training, each individual meal was higher or lower in carbohydrate and they said that as of this time, 2017, that that represented the recommended eating strategy, at least in terms of macronutrients.

Trevor Connor  26:27

I do appreciate at one point in the paper, they said they made their case for a high carbohydrate diet as needed, but they said only at times of performance. That what they saw in that group was when they were just training and they weren’t racing, they were just fine being on a lower carbohydrate diet.

Rob Pickels  26:44

It’s something that was interesting and, Trevor, I’d love to get your take on this. In this study, instead of being fully random, they allowed the race walkers to kind of rank the diets that they would prefer and they tried to put individuals matched with their preferred diet. So some regard, I can see this as potentially beneficial, I do think that the subject maybe has some influence in the results. If you have somebody who swears that they’re a high carbohydrate person and you force them to be a low carbohydrate person, you have to wonder are they going to give their best effort when it comes to the testing, but at the same time, the other part of me is like, well, this isn’t truly random. I don’t know how I feel about this as a strategy.

Trevor Connor  27:31

Yeah, I’m mixed because this is the problem you have when you do dietary interventions. It’s impossible to make them truly random because people aren’t going to know what they’re eating. So you can’t make all food look the same. So they’re going to know if they’re eating a lot more carbohydrates or they’re going to know if they’re eating a lot more fats, if they’re eating a ton of avocados and steaks, they know they’re on the high fat diet. If they’re eating a whole lot of rice and pasture, they know they’re on the high carb diet, they just can’t get around that. So I can see the rationale for saying, if you have somebody, you put them on a diet that they truly don’t believe in, well, they might intentionally or subconsciously not perform as well because they don’t believe in it. If you have everybody on a diet that they believe in and one group doesn’t perform as well, then you’ve gotten rid of that subconscious element because you know they’re giving it their all. So I can see the rationale for that.

Rob Pickels  28:29

There is something that I do like about this study design is that it was completed during training camps and so essentially, it was national team level racewalkers, there was approximately 30, actually 21, but they had 29 data sets, I think because there was some athletes that did two training camps and that allowed them to have relatively equal amounts in each of the different dietary interventions, but it also because it was a training camp, it allowed them to control the training, to control the food because the training camp was literally serving them the food and I do think that that’s really important because one other thing that you see in nutrition studies is that when people are allowed to go home and eat, oftentimes they’re not very compliant to the study design and they they sneak in a HERSHEY’s Bar every once in a while, and that can really foul up the results.

Trevor Connor  29:21

That is always one of the issues with dietary studies is the self report. Are they truly reporting what they ate, are they truly sticking to the diet? The best dietary intervention studies, you literally control what they eat. They have to come to whatever center and eat there and eat where they’re being observed, which is really difficult to do, but I will say when you have elite athletes who are training at a center and live at a center, it’s actually one of the easier places to do it.

The Fast Talk Team  29:51

Hey, Fast Talk listeners, this is Trevor Connor. Would’nt it be cool to decide what Rob and I are going to chat about on an upcoming show or how about we answer a question on polarized training you’re dying to know. What about a 30 minute zoom call with Robert and me on your favorite sports endurance topic. This is all possible to become a Fast Talk Patreon member. We have four monthly membership levels to fit your level of support. If you enjoy Fast Talk, help us stay independent in dishing out your favorite sports science topic by becoming a Fast Talk Patreon member, you can join us at

Rob Pickels  30:26

Okay, so let’s let’s dive into what they found. I’m going to let you start, I don’t want to steal your thunder. I know it’s something I want to talk about, but if you want to talk about it, I’m going to give it to you for so.

Trevor Connor  30:35

If you’re gonna give me the thunder, I’m gonna take the huge thunder, which is the ultimate conclusion. Which was all groups improve their aerobic capacity, but only the low carbohydrate high fat group did not see performance improvements.

Increased Fat Oxidation Does Not Mean an Increase in Performance

Rob Pickels  30:48

One of the biggest reasons that that occurred and everybody forgets this, if they knew it, they forget it, it seems. When you increase your fat oxidation, it takes a lot more oxygen to be able to oxidize that fat and so economy goes down. You’re consuming more oxygen to do the exact same thing. So any changes in VO2 Max get blown away because you’re still working at the same fractional utilization and that means oftentimes you do not see performance improvements.

Trevor Connor  31:21

No agreed. So I think another important thing to bring up about this study is the context. It was part of a series of studies that Dr. Hawley wrote, from about 2015 to 2017, that as he said, was the nail in the coffin on the high fat, low carbohydrate diet and I do think it’s important to mention one of the earlier papers that he wrote, called ‘carbohydrate dependence during prolonged intense endurance exercise’, it was written in 2015, it was a review paper and the gist of this paper that’s really important is that, well, those diets can improve fat oxidization, you see that they actually impair glycogenolysis, which is very important to your ability to use glucose for fuel. So put in simple terms, what that means is, yeah, your fat oxidization might improve. If you’re going at a slow speed, you’re gonna be able to go forever, but if you’re in a race and there’s moments of high intensity, where you really need to rely on glucose for fuel, it’s not going to be there and you’re not going to win the race.

Rob Pickels  32:29

Yeah and I think that this is an important point, because in almost all competition, success is defined by those periods of hard intense work, across a lot of race durations. Eeven, in my opinion, even in an ultra marathon type situation where you’re limiting the amount of high intensity you’re doing. You’re you’re doing Leadville, 100, you are you’re going hard up hills, even if you’re hiking, you have to be able to work at relatively high workloads. It’s relative. It’s not the same as if you’re in a criterium, but the thinking ultimately is that well, as the event gets longer and longer, I can rely on fat more and more, but I don’t know that you ever get to the point, unless you’re just walking across America casually, that a lack of glucose oxidation is beneficial for you.

Trevor Connor  33:26

So I think two other important things to point out which you can’t read in the study. So I actually did interviewed Dr. Hawley after he wrote this paper and I think it’s just fun to point out that said, we didn’t write it in the paper, but those racewalkers who were doing the high fat, low carbohydrate diet, were really unhappy, grouchy people. They were never feeling good when they were training, they were never recovering as well. They were just unhappy.

Rob Pickels  33:54

In some regard. They do. I don’t want to say they get to that, but if you look at rating of perceived exertion across the groups, the RPE was higher in the low carb, high fat situation.

Trevor Connor  34:07

Look, the other thing to point out, we did do a podcast with Dr. Timothy Noakes and we’ll put what number that was in the show notes, but he actually addressed this in that podcast and his counter argument and we’re not going to take sides on here, we’re just bringing up the research and I think this is for everybody dive into this and see where you stand, but Dr. Noakes argument was this paper was a three week intervention and when you move somebody from a high carbohydrate to a high fat diet, there is a transition period where you are definitely going to see a decrease in performance, but he said the issue with this study is they didn’t go long enough. If you do it six months to a year, you see them adapt and then you actually in his opinion, see an improvement in performance.

No Definitive Studies on High Fat, Low Carb Diet

Rob Pickels  34:51

Trevor, has there been any definitive studies that investigate that and I’m I’m really asking because I’m not aware of any, but I will say that is the common argument for proponents of high fat, low carb and I would love to read that research if it’s available.

Trevor Connor  35:07

So again, I can’t remember the one off the top of my head. but Dr. Noakes did cite studies that were that were longer term that he said, made the case. I think this is a real gray area. I’m not going to jump on either side of this. I think it is still, in my opinion, the nail is not in the coffin. I think there is more research to be done here. I think there’s a lot of gray area and at least personally, I don’t have an answer on this.

Rob Pickels  35:35

Well, I’m a carbs for life kind of guy, Trevor. So if the more research comes out and supports high fat, low carb, I’m just going to I’m going to shut my eyes to it and pretend it doesn’t exist

Trevor Connor  35:45

So if you’re a cyclist, and you’re in a race who has a lot of attacks like a crit, I think you need those carbohydrates. If you’re an Ironman athlete where there’s no attacks, you don’t have to have that big one minute spurt, it’s a lot grayer to me.

Rob Pickels  35:58

No and I do think that you’re entirely right in that the correct answer oftentimes relies on the needs of the event and the needs of the individual athlete. Carbs for life.

Trevor Connor  36:11

Just to drive you nuts. So there are three macronutrients fat carbohydrates, protein, the only one that is not essential is carbohydrates. You will die if you don’t eat fats and protein. You can actually live if you don’t eat carbohydrates.

Rob Pickels  36:26

But can you live well?

Trevor Connor  36:27

Oh, who cares about that?

Rob Pickels  36:30

Trevor, I think it’s time that you educate me on the molecular basis of training, adaptation.

Trevor Connor  36:36

I love that I was so excited about this paper and you absolutely dread this one.

Rob Pickels  36:43

It’s not that I dread it, it’s that I understand what’s outside of my skill set and my jurisdiction and biochem is an area that you do not want me educating other people and so that’s why I was like, I’m gonna come into this as the student, maybe asked some smart questions, but really let Trevor have his moment on this one.

Molecular Basis of Training Adaptation

Trevor Connor  37:05

So the answer to that question is no, we’re not going to dive deep into this one. I recommend anybody who is interested in this side, anybody out there who is an exercise physiologist, studying exercise physiology, if you’re a coach who wants to know more about the biochemistry, this is a must read. This is a really important paper, but it is deep. Any key papers that I want to go back to again and again and again, I write a summary of them. I have never written a summary as long as the one I wrote for this paper and by the time I was getting to page 17, 18, my notes were go back and look at the paper because I was getting tired of writing all this. So it could have been longer. It is a thick paper. Sorry, did we even say the name the it’s ‘the molecular basis of training adaptations’. It was written in 2007. To give you some context, we did that previous seminal podcast on the work of Dr. Larson and we talked about a paper that he did that really dived into the biochemistry. That paper was what 2011 and I don’t know if Dr. Larson looked at this paper by Dr. Hawley, but you saw a lot of the same themes. So they were definitely reading the same research. Remember, this is 2007. This is right when Dr. Seiler was coming up with the polarized training concept. This paper tries to dive deep into when we talk about training adaptations. So you go and he didn’t just talk about endurance training. So this is both resistance and endurance training. When you go and do a block of endurance training, or you go and do several weeks of resistance training, what is molecularly going on in the body and how does that produce the adaptations? Whether it’s endurance improvements or mostly mitochondrial biogenesis or whether it’s hypertrophy in the muscles. What is going on and he dives deep into all the steps, all the pathways, all the messengers, all the proteins that produce these adaptations and it was to get at, so he explains all these pathways and then at the end, he goes, now let’s look back and try to figure out how does endurance training affect these pathways? How does resistance training affect these pathways and the very end of the paper, so I’m going to kind of go to the end first. He drew a little graph which I have seen versions in multiple, multiple papers since. I can’t say for certain Dr. Hawley was the first one to draw this graph, but it’s the first place I ever saw it and it just shows the basic pathways of resistance training and endurance training. So endurance training at activates something called AMPK, which then goes to increase transcription of my favorite term PGC, one alpha and that produces mitochondrial biogenesis. which is basically your aerobic adaptations. In resistance training. It’s mostly the IGF. So insulin like growth factor, basically a hormone gets upregulated that activates AKT, which then activates mTOR Raptr. So mTOR is mammalian target of rapamycin and I promise I’ll be done with all my terms soon. So when they talk about resistance training. On endurance training, I was talking about PGC one alpha, the equivalent on the resistance side is this AKT mTOR pathway and that ultimately leads to protein synthesis and hypertrophy, but what’s really important in this graph is they show that raising AMPK actually has an inhibitory effect on mTOR. So when you do endurance training, you’re going to inhibit your body’s ability to produce hypertrophy to increase muscle size. You don’t see an equivalent inhibitor the other way. So going and doing resistance training is not going to impact endurance adaptations.

Does strength training hurt or help endurance sports?

Rob Pickels  41:17

Yeah, we in some regard, we discussed the output of this with Dr. Ben Ronstadt, back in episode 211. We titled ‘does strength training hurt or help endurance sports’ and when we had a great conversation about the research that Dr. Ronstadt has done that was interventional, looking at strength in endurance training and so pairing that with Dr. Hawley’s paper here, it gives you the full picture of why Dr. Ronstadt didn’t necessarily see that there is in some regard an interference. If you’re doing a lot of endurance training, your ability to have hypertrophy is relatively small. Endurance trained athletes are not going to be bodybuilders, but that endurance training can benefit from strength training and you can actually see some improvements there and I think that that traffic goes back to this pathway that you’re talking about and the direction of inhabitation between endurance towards a resistance and vice versa.

Trevor Connor  42:15

I think there’s a lot of really good stuff in this paper, but I think that graph at the end is a great summary of what the whole thing is about and big part of what it’s contributed.

Rob Pickels  42:28

I will say though, molecularly, there is no inhibition here, but they do point out in this paper that with hypertrophy, as the muscle fiber gets bigger, it actually gets more difficult for oxygen to diffuse and so there is potentially a negative benefit, but it’s not in a biochemistry sense. It’s almost in a purely mechanical sense.

Trevor Connor  42:47

No, I agree completely. I think another important thing to point out in this paper, and again, we’re just gonna dip our toes into the biochemistry here, if you want to dive deep into the biochemistry read this. Otherwise, we’re gonna be throwing so many different chemical terms at you, I would be turning the episode.

Rob Pickels  43:07

No, can I just say I have an advanced degree in physiology and Trevor, as you do as well and at first, I was gonna say reading through this, there was at least a dozen terms I had never seen before, but now that I actually have the paper in front of me, there’s more than a dozen terms I’d never seen before. So yeah, this is bio biochem 401, not 1010.,

Four Steps within Biochemical Cascade

Trevor Connor  43:31

No, it’s way up there, but I think and we’ve talked about this before, as matter of fact on a recent episode with Dr. Seiler, we talked a little bit about this, but at the start of the paper, he talks about what he calls the putative primary messengers. So explaining what that means, you go out and do some sort of training, whether it’s riding your bike, going for a run or lifting weights, that action has an effect on your body and what are those very first effects that it has? Basically, those effects that have those things are what then start this whole cascade, this whole biochemical cascade that ultimately leads to adaptations and what he identified is there are four and the first one is mechanical stretch. So literally, you’re lengthening and shortening the muscle, your body responds to that and that can lead to both some of the endurance adaptations we talked about and actually a lot of the resistance training adaptations that we talked about. The next one is calcium release and uptake in the muscles. So every time a muscle contracts, it has to release calcium and then suck all that calcium back up and that causes the muscle to relax. Your body responds that particularly when you are doing enough training that fatigues and it doesn’t suck all the calcium back up. So you started having some calcium lingering around in the muscle sarcoplasm. The next one is oxidative stress. So particularly endurance training, far less resistance training will increase oxidative stress in the muscles and in your body and your body will respond to that and that will also produce an adaptive signal and then the last one is within the muscle cells, this balance and this is what we talked about with Dr. Seiler. This balance between AMP and ATP. So ATP, adenosine triphosphate and AMP, adenosine monophosphate. So one has essentially the same molecule, just one has only one phosphate and one has three phosphates. The ATP is what your body uses for energy. That is, anytime your body’s doing anything that requires energy, it’s using ATP, but the way the energy is released is by breaking off one of those phosphates. So AMP is the low energy form. So when you’re doing something that’s very high energy, you’re going through a lot of ATP. So you’re producing ATP and then AMP, your body can’t keep up if you’re at a really high intensity. It is breaking down ATP faster than it’s rebuilding ATP. So you’re gonna end up with more ANP in your muscle cells and your body responds to that and that produces an adaptive signal, but the one that I love is the two really important ones in endurance training are that calcium, the release and reuptake and the AMP, ATP balance because  AMP, ATP balance, as I was just saying, that really only gets impacted when you’re doing really high intensity activity and it seems to hit the pathway produce those adaptations very rapidly, but the issue is as you adapt, your body gets really good at rebuilding the ATP. So you stopped seeing that imbalance as much. So that is why when you’re doing high intensity training, you can see really good adaptations for about six weeks, but then you start to plateau because that signal gets really, really ramped down. That calcium pathway to adaptations, that’s what you tend to see when you’re doing much longer, slower endurance training and it never really fully adapts. So you keep hitting the that adaptive pathway, you can keep seeing improvements for years and years and years and that’s a bit of a simplification, but that in essence is using biochemistry to explain why the polarized training model is such an effective model.

Mechanical stretch and mechanical stretching

Rob Pickels  47:38

Yeah, Trevor, I think that it is important to be looking at this and we can take this thinking as well to the mechanical stretch side, where if you look at the load the muscle is under on long continuous endurance training, as opposed to short, high intensity strength training, the body actually responds in two different ways by signaling to those different mechanical stretches and this is where volume as well, like you said with the calcium, volume is really important for that pathway, but also based on mechanical stretch as well because we can alter the signals that occurred downstream when we have those light bulb continuous stretches, but ultimately, what we’re getting at is volume and intensity are both important and these are the reasons why to become a well rounded, high functioning endurance athlete. You need both of those.

Trevor Connor  48:34

Yes, exactly. So we’re Rob, we’ve dipped our toes. Do we want to put our foot or full leg in anywhere, think dipping the toes was enough for this one?

Rob Pickels  48:43

Oh, my God, Trevor. I’m afraid. I’m afraid to go any deeper than this to tell you the truth, man. Somebody out there is going to call me out and be like, you idiot. You said blah, blah, blah and it was wrong. Like I’m not gonna say anything. Forget that. You guys want to know more about this? Download the paper yourself?

Trevor Connor  49:03

Well, look, I will say it right now. Everything I just told you, is a simplification of what’s in the paper and I’m sure in simplifying it, I didn’t get it quite right. That’s always the danger of simplifying. So yeah, if you really want to understand the complexities, if you really want to understand the whole process, if you don’t want that simplification. Go read this paper.

Rob Pickels  49:26

Yeah and then you don’t have to read the 281 papers that they reference to make it.

Trevor Connor  49:31

That’s insane, isn’t it?

Rob Pickels  49:34

It really is, in all honesty.

Trevor Connor  49:36

I have pointed to reviews and said oh my god that has like 110 papers that it cites as a big review. 280 Good lord.

Rob Pickels  49:45

But that’s why it’s important. I mean, there was a lot of great work that occurred before this. This paper is not necessarily about discovering something that’s new, but it is about assimilating known knowledge, putting it in one place, making it understandable and consumable for people and I find a lot of value. I think, Trevor, we’ve done two of these seminal episodes and they’ve had review papers in both of them.

Trevor Connor  50:08

Yep. I love review papers. Maybe it’s just me being lazy, saying I don’t want to go and read those 280 papers, I’ll just read the one that summarizes them. I love that ability for somebody to read all the research and then try to pull it together and say, here’s what we think it means. I love the thought process behind that and I think that is what is really important about this paper, Dr. Hawley and the other person who wrote this with him was Dr. Kofi. They went and did their research. They found those nearly 300 papers, pulled them all together and said, here’s what it all means. Here is essentially the biochemistry as we currently understand it, of training adaptations and I don’t think anything is thorough as this, at least from from what I’ve read anything as thorough as this had been written to this point.

Rob Pickels  51:01

Yeah, I agree, Trevor and I’m actually glad that you called out the second, technically the first author on this paper, Vernan Kofi. Were discussing Dr. Hawley because he is the thread that’s tying these together. That’s the theme today, but there is at least a dozen authors who we haven’t mentioned across these papers and I think every researcher has teams and those teams are critically important to producing quality research.

Trevor Connor  51:27

Agreed and certainly, to that point, you’ll look at that 2017 paper about the race walkers. There were a lot of people involved in that one.

Rob Pickels  51:36

Yeah, from seven different institutions pretty much all Australian though.

Trevor Connor  51:40

But it was a big study.

The Fast Talk Team  51:43

For both beginners and veterans polarized training is the best way to get fast and stay fast year after year and this is the perfect time of year to be thinking about how polarized training can help you in our new guide featuring Dr. Stephen Seiler explore fascinating and helpful topics like How Polarized Training is Different from Sweetspot, How to Bust Out of Performance Plateaus, How to Polarize All Aeason, How to Build Durability and How to Time Your High Intensity Work. With this complete guide from Fast Talk Labs, you’ll have everything you need to polarize your training like a pro and unlock your leap. Learn more at

End of Today’s Episode

Trevor Connor  52:26

Well, Rob, we covered three. As I said, we could have easily done 50 with Dr. Hawley and still not covered his full body of research. So any last thoughts?

Rob Pickels  52:35

Man, I just I just want to know who’s next. I’m excited for our next seminal. I’d love to hear if anyone wants to point out a researcher that they think is worthwhile, then I’m open to suggestions, but there’s so many great ones out there. I can’t wait for our next recording like this.

Trevor Connor  52:51

Well, let’s leave it there as Rob said, if you have suggestions, let us know who you’d like us to cover. Otherwise, this won’t be our last and I’m personally really looking forward to our next seminal podcast.

Rob Pickels  53:03

Awesome. Thanks, Trevor.

The Fast Talk Team  53:05

That was another episode of Fast Talk. Subscribe to Fast Talk, wherever you prefer to find your favorite podcasts. Be sure to leave us a rating and review. The thoughts and opinions expressed on Fast Talk are those of the individual. As always, we love your feedback, tweet at us at @fasttalklabs or join the conversation at Learn from our experts at or help keep us independent by supporting us on Patreon. For Trevor Connor, I’m Rob Pickels. Thanks for listening!




Bartlett, J. D., Hawley, J. A., & Morton, J. P. (2014). Carbohydrate availability and exercise training adaptation: Too much of a good thing? European Journal of Sport Science, 15(1), 3–12. Retrieved from 

Burke, L. M., Ross, M. L., Garvican‐Lewis, L. A., Welvaert, M., Heikura, I. A., Forbes, S. G., … Hawley, J. A. (2017). Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. The Journal of Physiology, 595(9), 2785–2807. Retrieved from 

Coffey, V. G., & Hawley, J. A. (2007). The Molecular Bases of Training Adaptation. Sports Medicine, 37(9), 737–763. Retrieved from 

Furrer, R., Hawley, J. A., & Handschin, C. (2023). The molecular athlete: exercise physiology from mechanisms to medals. Physiological Reviews, 103(3), 1693–1787. Retrieved from 

Hawley, J. A., & Bishop, D. J. (2021). High-intensity exercise training — too much of a good thing? Nature Reviews Endocrinology, 17(7), 385–386. Retrieved from 

Hawley, J. A., Brouns, F., & Jeukendrup, A. (1998). Strategies to Enhance Fat Utilisation During Exercise. Sports Medicine, 25(4), 241–257. Retrieved from 

Hawley, J. A., Hargreaves, M., Joyner, M. J., & Zierath, J. R. (2014). Integrative Biology of Exercise. Cell, 159(4), 738–749. Retrieved from