Dietary carbohydrate is an obligatory requirement? Louise Burke

Dietary carbohydrate is an obligatory requirement?  Louise Burke



and because I'm not sure what has been covered at the other contributions to the conference I thought I'd try and just put a bit of context around some of the things I'll be speaking about I think the first thing that would be important to understand is just what goes into making performance and of all the things that you talk about measuring at conferences like this I can assure you the most difficult thing that anyone can ever measure is some human performance particularly for an elite athlete with the kind of resolution and reliability that's some important in my field and one of the things it's also important to really know is that so many different things go into making up performance on the day and even if you can change one aspect of all these little contributions here it may not be the limiting factor and therefore have them some flow on to the actual performance but next slide please today we're going to be talking about one aspect of this pathway and that is looking at some metabolic flexibility and I've defined that on the next slide as the ability of the athlete to be able to have available fuel supplies and the ability to use them at the race and for the length of time that their event requires go ahead the next slide please and just to put a little bit of more context around this some interaction between training and competition I just wanted to point out some differences in philosophies and that is during during the training phase we're looking at ways in which we can further the adaptation that exercise is bringing to the human but during the competition phase we're looking at ways in which we can overcome some of the limitations to performance and in some some areas the kinds of contributions will be directly opposed in the training and competition phases so if we talk about the topic for today and that is some looking at where the carbohydrate is really important to elite athletes and endurance events if you're a Twitter follower likes to the world is simplified these days it's almost a combat sport in that sports nutrition seems to be about those in the red corner loving carbohydrates and those in the blue corner loving fat and we're going to Duke it out to see who's the ultimate we know I think it's a very unfortunate perspective on sports nutrition that that's all a one-size-fits-all or a black-and-white view of things and what I've been trying over my career to do is to provide a bit more complexity or more understanding about things so there's never announcer to do something work but more so under what situations might this be appropriate and under other situations might that be appropriate so if we go to the next slide and look to see what people who don't read Twitter already on this topic we can find even in the peer-reviewed literature there's an unfortunate bias towards a very simplistic view of sports nutrition next slide please and if we just take this review as a as an example of this here we can see some of the the current ideas about carbohydrate that it's an old idea that we've had this period of time we've been telling athletes universally to eat large amounts of it regardless of their athletic goals this is largely been a conspiracy theory behind it that carbohydrates and unfortunate nutrient because of what it does to insulin responses but if we move our diet away from carbohydrate we can adapt to that and that's a great thing because of the plentiful supply of fact that we have available even in the lens of athletes and this can be something to enhance endurance performance and the core goes out to overturn this Universal message of the high carbohydrate diet for athletic performance next slide please this is not some the only peer-reviewed paper to to try and promote this kind of narrative here we have some other reviews which give us this some universal message that the basis of sports nutrition is promoting a high carbohydrate at all times for all athletes for all goals next slide please so before we go any further into the lecture what I'd like to do is really provide the truth about what the current sports nutrition guidelines say in view of carbohydrate intake can we can break it into the training phase and the competition phase separately and we no longer talk about high carbohydrate diets or even absolute amounts of carbohydrate all in sports nutrition but rather we talk about carbohydrate availability as looking at the amount of carbohydrate that's consumed in comparison to the fuel needs of the muscle to undertake the workload that's being done in training or competition phase and in fact the guidelines now talk about athletes needing to periodized both the total amount of carbohydrate they're consuming because of the different types of fuel requirements I'll have over different days or due to parts of their season or different kinds of events but also that there are some kinds of sessions in which it's good to have high carbohydrate availability to drive performance but in other sessions it's less important and there may be even some advantages and we'll hear about this in a later lecture on having the muscle do exercise under low carbohydrate availability circumstances when we come to the competition phase again it's a matter of matching carbohydrate availability to the requirements of the event but in this scenario the message is to try and match those fuel requirements both in terms of providing the muscle with a very efficient fuel but also in providing the brains the OP unity to sense it so that it can feel better and drive the pacing towards better performance so I think it's necessary to have that background that we do no longer provoke this some Universal high-carbohydrate message to set things right before we look at some alternatives to that next slide please so here's my very simplistic view of what the muscle has on offer in terms of fuel substrates when we get into that competitive phase and if we go to the next slide we can see that there's been a number of different strategies used over the years to try and find ways of making those substrates either more available or more optimally or efficiently used and if we look at the ways in which carbohydrate has been manipulated both to increase the muscle glycogen storage or the amount of exogenous glucose coming in there's very good evidence to show that in events where fuel is limiting from glycogen that these kinds of strategies enhance performance and even in the non glycogen limiting sports there's now good evidence to show that taking in carbohydrate during the event can have a role in improving performance through the the mouth sensing of carbohydrate and the brain response by contrast if you look at the different kinds of strategies which have been used to try and make fatty acids or sources of fat available to the muscle in larger amounts acutely there's very little evidence to show that leads to better performance and so we would say that it's not just the availability effect that's the limiting factor as Francis's told us previously but rather we need to find ways in which we can drive the muscle to be able to utilize it more efficiently so we'll now look at the two strategies at the bottom of this slide waves in which we could try and adapt the muscle either in a chronic form or in a shorter form just before competition as a way of trying to provide both the availability of the fatty acids as well as an improved capacity to use them as an exercise fuel next slide please so if I take all the literature which is looked at these kinds of strategies in trained individuals with a chronic a patient of a high-fat diet we can break them down into two different forms ones in which there's been a ketogenic form of the low-carb high-fat diet in which carbohydrate is very restricted leading to prolonged ketogenic responses fat intake is very high and you can see that that means by omission that protein is also kept at a very moderate level we can compare that with the other strategy which has been used which is a more flexible diet in which fat is also increased but carbohydrate is certainly kept below the muscle fuel needs for most endurance athletes and their training loads but not as dramatically as the ketogenic diet so I've chosen to summarize all the studies which have had either either of these approaches in trained individuals with the measure of performance that is meaningful in my world of sport and if we move to the next slide we can see I've been able to summarize all those studies on a single graph now I'm not expecting you to read that slide I'm just wanting to give you the perspective but really the amount of literature we're dealing with is very small and I've tried to summarize what the bottom line was in that last column and you'll see I've tried to be generous in not just saying yes or no but perhaps trying to identify from the studies the conditions under which these these strategies might be useful you can see that there's one study that's picked out in blue and that's the only study that has appeared until recently and in the peer-reviewed literature using the ketogenic form of the low carbohydrate high fat diet and it's this study that's getting all the airplane now and seems to have been reinvented by many of the people who talk about it if we go to the next slide we'll have a look at it in a bit more detail this some study was well controlled study in which five world trained cyclists were in a hospital situation so they were provided with a well monitored diet it was a study which involved the exposure to four weeks of the ketogenic high-fat very restricted carbohydrate diet with training with endurance rather than performance time to exhaustion pre and post you can see there's an order effect in this diet that the subjects had an extra four weeks of training to be taken into account as well as their exposure to the diet when you look at the pre to post endurance if you have a look at the next slide we can see what happens to muscle glycogen under those circumstances and you can see that there's a reduction in muscle glycogen in the pre exercise situation as a result of the exposure to the high-fat diet and there's much small utilization of that glycogen throughout the exercise bout and we should point out at this moment that the exercise is undertaken at about 60 percent of vo2 max so it's very low intensity exercise compared to what elite athletes would be doing in even the longest events that you would see in the Olympic Games if you move to the the next slide so we can see the sort of the money shot the effect on endurance there was no difference in endurance between the pre and post conditions and this has been even further explored by looking at the results of the individual subjects on the next slide and you can see that the results of this study are really largely driven by one subject who had a much larger response to the high-fat diet was able to go much longer after the high fat diet and an extra four weeks of training than the other subjects and so really this whole philosophy of the low-carb high-fat diet or at least the ketogenic form of it really is reliant on that one person I'd love to meet him and shake his hand if you have a look at the next slide though I've chosen to provide to you the interpretation of the study as was written by the authors at the time and they noted the their marvelous results were that they were able to show that under these some periods of adaptation or exposure to this very limited carbohydrate intake the human body could adapt to learn to be able to have the same capacity for low to moderate intensity exercise as with a high carbohydrate diet but in other parts of the study or other data that were collected in the study both showed that this was at the detriment of the athletes ability to do high-intensity exercise and it's interesting to go back to this finding because it's not very unclear from the way that it's been talked about enough in the current media if we go to the the next slide then I think we can say that adaptation to the high-fat diet for a prolonged period at least at the coveted current level of evidence doesn't show any major benefits or consistent evidence of benefits and so therefore we might move to the final strategy which is trying to adapt the athlete to both the high-fat diet but then restore carbohydrates so that they would identical in theory at least have the best of both worlds with fuel sources both being available and available to be used efficiently and if we go to the next slide you can see again I've tried to summarize the literature and you can see here again that there's a very small number of studies on which we're trying to make our conclusions and again I've tried to be generous with picking out different scenarios under which this kind of them adaptation might be useful and so we'll go through some of these studies in order to pick these out so the next slide simply gives you an overview of the model that we spent a decade trying to pursue where we had athletes Undertaker a five day period of adaptation to a high-fat diet which were able to show retool the muscle to be able to be better at utilized and fatter than exercised substrate we then after that period put them back on one day of a high carbohydrate diet to restore glycogen and in the first study that we did we had them then perform a period of exercise with a Time Trial at the end under conditions of low carbohydrate availability if you go to the next slide you can see that the expected changes in glycogen would occur that it's reduced with the period of the low carbohydrate diet but with one day of carbohydrate restoration we restore glycogen levels again the next slide shows what happens when you exercise under those conditions and you can see with the carbohydrate utilization figures over that time 120 minutes of steady-state exercise there's a reduced reliance on carbohydrate as an exercise fuel as a result of that adaptation despite the fact that the muscle is full of glycogen next slide if you have a look at the time trial at the end of that bout though we saw no difference in performance from a statistical significance point of view but some differences and some individual variability that a coach or athlete might be interested in next slide please if you have a look at the individual responses you can see that it's largely due to one subject you've had a very bad response to the high carbohydrate diet when under the conditions of low carbohydrate availability for performance and if you have a look at the next slide you can see that that's explained by the effect of performing under low carbohydrate availability on blood glucose levels and in that subject there was a very marked response if you go to the the next slide you can see that we repeated the study again this time we had the performance being done under conditions where we fed breakfast of carbohydrate fat carbohydrate throughout the exercise bout despite the potential supplies of carbohydrate we still saw these differences in utilization by the muscle throughout the steady-state bout but this time when we had a look at a time trial at the end of it on the next slide you can see so that there's a hierarchy there you can see what happened in two of the studies together that despite putting more carbohydrate back into the picture you still retain a difference between the utilization of carbohydrate after the fat adapt ation and in the next slide we'll see the performance changes and you can see pretty well no difference in performance of the time trial as a result of that adaptation despite the very different substrate utilization and availability we wondered whether we simply hadn't gone long enough with our studies and so we did the follow-up study on the next slide where we went out to a four-hour bout of exercise with an one hour time trial at the end again very high amounts of carbohydrates being consumed before exercise during exercise and with high levels of glycogen in the muscle we still say there's very robust differences in carbohydrate utilization with the federal outpatient next slide we traced what happened with the carbohydrate that was ingested during that bout and found that there was no effect of the federal apt ation on that therefore convincing us that it was simply a changing glycogen utilization patterns as a result of a fad apt ation and in the next slide we also saw a difference in performance of a marginal trend that a statistician would have said was insignificant but again something that might be abuse in the world of sport where these small differences make a difference to the outcomes if we have a look at the next slide to see what happens with the individual differences again we see one subject – as an outlier that it creates that difference and when we looked at what was happening with that subject he had a bad experience with consuming the large amounts of glucose during that trial and had a gastrointestinal upset we've still left that data in but that's large and the reason for that difference and in the next slides when we were challenged by the idea that we might have had a type 1 type 2 error because of the small sample size and we ran some more subjects next slide you can see that once she's add more subjects you completely wash out the differences of that individual subject and so we began to feel that there may be just individuals or individual scenarios for which there's some this strategy might be useful if we move forward to the to the next slide we did with looking at some of the the muscle changes identified the wave in which the adaptations were occurring in the muscle to increase hormone sensitive lipase to increase the CD 36 and so we can explain what was happening in the muscle but we couldn't explain why that wasn't translating into a performance difference until we started looking in the opposite direction next slide and that was when we teamed up with Lawrence Street and trench selling worth to have a look at what was happening to the carbohydrate side of the story and we came across the finding that our adaptation strategy certainly upregulated fat utilization but it was at the detriment of carbohydrate utilization pathways and in particular there was a down regulation of PTH activity if you look at the next slide you'll see why that's important this is data that comes from a study from Tim Noakes is lab where they looked at a fat adaptational carbohydrate restoration story and this time implemented a protocol of measuring performance in a pure sense of having athletes do 100 kilometres time-trial there was no significant difference between the performance of their hungary kilometer time trial between a carbohydrate rich diet and the fat adapt ation plus carbohydrate restorations story but it wasn't the significance of the total time that was important in the study it was looking at pieces within the study and you can see on the graph there these are the data showing the power output swings and cyclists were required to do a 4k sprint in the middle of this time trial and in the next slide you'll see what happens when they start moving into the higher intensities you're doing a 1k sprint where we start seeing significant detriment to performance of that high-intensity exercise and so our bottom line in looking at our literature on the next slide was to say yes there's some great things that that adaptational do in terms of enhancing fat utilization but the detriment to the carbohydrate story makes that suddenly start becoming not a good idea for athletes who need to do high-intensity work even when it's just small but very event changing strategies within a race it's not how long you can go at 60% of vo2 max and the peloton it's whether you can sprint to the line or surge up the hill etcetera the determines the outcome slide so we were thinking about some some of the ways in which you could communicate these ideas to an athlete about why it was important not to throttle your ability to move carbohydrate efficiently through the TCA cycle and some of the the words that I would use to efforts were to describe how efficient carbohydrate oxidation is in terms of providing a ATP for the amount of glycogen that you've got but also the idea that it's a very efficient fuel in terms of oxygen utilization that compared to fat oxidation you'll get a greater yield of ATP for the amount of oxygen that is supplied to the muscle next slide please we also pointed out to the athlete the whole range of disadvantages of undertaking some of these fad adapt ation strategies apart from being very difficult to follow there are a lot of inconveniences in terms of how people feel in training how it might interfere with their ability to monitor their training or do the high-intensity sorts of training that it's important to drive performance so we're very surprised over the last three years to find a reamer gence of this high high fat low carb story next next slide so we'll move to the next slide after that largely driven by the popular media through books and through all the social media we now have and if you move to the next slide you can see examples of lots of different ways in which this some idea has been communicated through YouTube through Twitter through Facebook you name the social media there'll be a some narrative that's been driven behind it with very emotive stories next slide there's a lot of information that's coming out that height high-performing athletes have moved over to this trend and next slide you can see also that the punters love it as well lots of people will come out with their anecdotes and testimonials about how terrific the changes being for them next slide please so at the end of last year I had the opportunity to respond to that in the absence of any new data I am trying to recapture the story to say is something what I've just told you then that the narrative I think has been distorted about what the real sports nutrition guidelines are that the disadvantage of on a short-term or a chronic high-fat diet would be to reduce metabolic flexibility and ability to use carbohydrate efficiently and there's not a good story that I would give to my athletes in order to support that but I did point out that it hadn't been adequately tested so in the last five minutes I just like to share with you some very very recent data that we've been collecting in the last four months of my life in a project we've called supernova where we've typed to take some of the highest performing athletes that we can get some recruited into our study we worked with some some elite race walkers we were able to recruit 29 of those race walkers from all around the world and I need to thank Jared talent one of Australia's best race walkers for his um contribution to making this happen probably 20 of these athletes will be performing in Rio and we had them undertake a three-week high volume training program with these being divided into three different dietary strategies we had the high carbohydrate availability strategy we've had the low-carb high-fat ketogenic diet and we also put in this new periodized approach to carbohydrate availability being changed around different sessions to meet specific goals and we've done a whole series of um testing pre and post now I can share a little bit of data it's all been crunched as we speaking I can show you just a quick snapshot of the training program around race walkers were walking 120 to 160 km on average some up to 200 K a week we had the three different diets produced by a chef to make sure they actually occurred and that they were enjoyable we were able to match the carbohydrate intake on the high carbohydrate in the periodized carbohydrate approach but it was spread very differently over the week or over the day but with the low carbohydrate diet we achieved the goals of keeping carbohydrate to less than 50 grams a day and we match the protein over the three diets so the data I just like to share with you today comes from looking at that little comment that I made earlier about what happens to the economy or oxygen utilization when you switch from a carbohydrate to a fat-burning beast and on the next slide I'll just show some results from a couple of different tests that we did I need just to show you just in background that time we tried to allow them to lose a little bit of weight over the period of the study but to try and energy match it as well as possible but in the carbohydrate diets that was achieved but was the low-carb high-fat diet there was a small weight loss which is associated with the loss of glycogen and water and in the next slide we'll see some of the the data about economy this comes from a graded economy test that was done pre and post this is a standardized test that's done amongst race walkers where they do a fourth stage economy walk on the treadmill over four different speeds it usually 12 13 14 15 K now which sort of moves them through the pace they would be doing at a 50 K race to a 20 K race and you can see the the change from peter post with the low-carb high-fat diet that they've now moved to um this is the second speed so about 13 you can K now so that's around about the 50 K space and if you go to the next slide we have a look at the economy or the oxygen utilization at that speed so this is as I said around about the pace of just um below the pace that they would be walking in a 50 K race you can see that the oxygen utilization increased in the low part of high fat group as a result of their diet even though they were now lighter so if we put that as a relative from via to max for that difference with also that would be greater and in almost all cases there was an increase in the use of oxygen about 4 mils per kilo or about that 5% as we predicted as a result of the exposure to the high-fat diet if you look to the next slide we had another test that was done pre and post this was taking them out and doing a 25k long walk at that same second speed around 13 K an hour this time the card groups and the periodized groups had a pre-event breakfast and carbohydrate during as would be followed by the guidelines whereas the the the low-carb high-fat group ate their low-fat high-carb breakfast and during the walk and again you can see from the RER data that we're moving to a high fat oxidation in that group I've just normalized and averaged out across the 25k and if we go to the next slide again we see that same story there was an improvement in economy with the periodized diet but a loss of economy or a greater utilization of oxygen for the same walking speed as a result of the low carb high fat diet and amongst the racewalking community your economy your ability to be able to produce speed for your utilization of oxygen that is considered a very important part of them performance so if I moved to the to the last slide and talk about why are some people seem to find this fat adaptation works for them because it's really important to confront what we're hearing about with anecdotes and testimonials about why people think it's such a good idea and these are the kinds of scenarios under which it might be either less detrimental or may have some advantages to the performance of athletes and they would be in events where if that utilization is important and where there's no requirement for an ability to work at high intensities or in events or scenarios or individuals in which it's not possible to take in enough carbohydrate to meet those guidelines next slide other reasons that we could explain why people feel marvelous or think they perform better when they're on the low-carb high-fat diets is certainly the bandwagon effect the order effect the fact that sometimes it's the first time people have started training properly or eating in a way that's organized and all the other ways in which people just love jumping on bagged wagons but the last time sideshows another reason why often people say that they enjoy or they do better on the the low-fat high-carb diet and this is just a example of this this is a piece of literature from the astray and newspapers which have talked about one of our football clubs following the low-carb high-fat diet after a visit by Tim Noakes and if you read the newspaper cutting very closely on the left side you can see that what they're actually doing is following a paleo diet which is not a low-carb high-fat diet and they're not even following that because they're having rice and milk as well so there's a big difference between what people say they're doing and what they think they're doing and some of the actual ideas that are being promoted so always have a grain of salt and so my final site leaves you with where I think we are with some the the low carb high fat message I'm aware of some new studies that have come out of the last some couple of months which are not intervention studies but they're cross-sectional studies looking at differences between athletes that have adapted to these diets for long periods of time I don't measure performance but they measure some interesting things about metabolism but when I go to the Rio I'll be interested not just in what's happening at the level of the muscle but what's happening in terms of athletes getting to the finish line as quickly as possible and my last slide sums up where I feel we're at now and based on the evidence and based on what we know about how important it is to be able to work at high intensities in almost every event that I can think of I don't think I'm at the point yet where I want to give up my interests and ideas and support around the high carbohydrate availability message and I'm hoping that there'll be some more opportunities to do research that can help work out whether there are further things that we need to look at in terms of the high fat diet or whether there are other strategies that we can use in the more periodized way in which we can actually improve metabolic flexibility overall thank you very much

3 comments

  1. for me this seems to me the highest degree of bullshit bro science.
    in some slides the write something of 7 or 8 days. this is absolutely not enough time to be fat adapted.
    6 weeks is the minimum. this is the same bullshit like giving a completely untrained human being a snickers bar and send him to a marathon and then conclude that he failed because of the carbs in the snickers bar.
    if you did some studies with people that have experience in keto diets then you would get other results.
    if you can't afford to consult the people with the right knowledge how to apply a keto diet for exercise, then please buy some books from phinney/volek about it or if you can't afford the few bucks for the books then watch some youtube videos from that people for free.
    or ask the record holder for running 101,77 miles in 12 hours. he is on keto too.

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