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Amby Burfoot has an interesting interview with Asker Jeukendrup on his Peak Performance blog. Jeukendrup has long been associated with PowerBar, but apparently moved over to the Gatorade Sports Science Institute as “global senior director” a few months ago.
I’ll be interested to see whether this signals a shift in direction for Gatorade: a couple of years ago, Gatorade relaunched its product line to feature a lot of mumbo-jumbo like “theanine to improve focus” and “B vitamins to help you metabolize energy” and so on. At the same time, it also disbanded its U.S. scientific advisory panel, which was composed of external scientists. One of the advisory scientists I spoke to at the time felt that it signalled an unfortunate change in direction away from high-quality, science-based product claims. Hopefully Jeukendrup’s hiring indicates a renewed commitment to science over marketing.
Anyway, the real point of this post is to recommend that you read the interview. Burfoot takes Jeukendrup through half-a-dozen topics of interest to readers of this blog, from beet juice to training on an empty stomach to whether thirst is a reliable mechanism to determine how much to drink. Somewhat surprising to me was Jeukendrup’s response when Burfoot asked if he could explain why beet juice seems to offer such a boost to endurance:
No I can’t explain them. I don’t know the mechanism that would cause them, and that bothers me. It also bothers the scientist who has done much of the work, Andy Jones, who is very good as you say. But he also can’t figure out why the beet juice is enhancing endurance.
I had thought some of the results from the Karolinska Institute in Sweden were shedding some light on how beet juice works — but then again, the explanation was complicated enough that I had trouble following it. So maybe it’s not as clear-cut as I thought. Still, the results have been repeated multiple times under different conditions, so in a sense the “why” is not essential.
I was most surprised by his comments on the “fat burning zone”. I thought that topic had been laid to rest.
@saundra: There’s a big difference between the usual “fat-burning zone” nonsense (i.e. the slower you go, the more fat you’ll burn!!!) and what Jeukendrup is saying. His group has done the most comprehensive studies looking at how two key factors interact:
(1) at low intensity you burn a higher proportion of fat, while at higher intensities you burn a higher proportion of carbs;
(2) the higher your intensity, the more TOTAL calories you burn.
When you put those two things together, there’s a peak where you maximize the total number of calories from fat that you burn — though the location of that peak varies widely in different people. Jeukendrup’s studies find that untrained people have their “fatmax” peak around 50% of VO2max (which corresponds to about 70% of max heart rate), while trained people have it around 60% of VO2max (75% of max heart rate). That’s a lot higher intensity than cardio machines are telling people.
At the end of the day, though — and this may be what your comment is referring to — does it really matter whether the calories burned come from fat or carbohydrate? This is still a big topic of debate. My feeling from the studies I’ve looked at is that it doesn’t matter (or if it does matter, the effect is so small that it’s not worth worrying about). But obviously Jeukendrup believes it does matter, and he’s certainly not alone in that belief.
This debate is actually pretty similar to the debate about whether training on an empty stomach makes any difference. The point there is to train your body to burn fat rather than carbohydrate. Again, there’s no real evidence yet that this improves performance in endurance events — but logically it makes sense that it might, and in the interview Jeukendrup says that he believes it will work once the studies are sensitive enough to detect the effect.
“does it really matter whether the calories burned come from fat or carbohydrate?”
It matters for marathon training, in the sense that you want to have a faster speed while using more fat as an energy source.
Also, Alex, I’m surprised you would say the “why” is not essential. I think you probably mean something else, like “we can figure out the why in time, but we do know it does work.” As far as science goes, isn’t the why the most important bit?
I agree with what I think John is saying – that it matters greatly if you are training to go fast in a marathon (in my case, marathon swimming). My understanding is that it is far more important to train the glucose-burning system if you want to go fast because it is trainable (and the same percentage change on a faster energy system makes a bigger total difference), whereas the rate at which you get energy from burning fat is essentially constant regardless of training (or can only change very little).
I am surprised by Jeukendrup’s statement that the total number of calories burned from fat does not continue to rise past 60% of VO2max.
Regardless of Jeukendrup’s reputation, I take anything from an employee of a sports nutrition company, especially a mainstream one such as Gatorade (or formerly Powerbar) with an extra grain of salt. I am sure, for example, there is no advantage to Jeukendrup saying there is a good, known reason why beetroot juice works b/c Gatorade is not going to market beetroot juice and if they are going to include nitrates (or whatever is responsible) then they really don’t need to give that away before they release a product.
@John: Yes, I just mean that the “why” isn’t essential from a practical point of view. If an athlete is considering using beet juice, the evidence is strong enough as it is. Of course I’m interested in learning how it works! But further refinements of the optimal dosage and timing and so on will probably come from empirical rather than mechanistic studies.
Of course, this is exactly the opposite situation to what we have with fat-burning, where we have lots of mechanistic data (“here’s why this SHOULD work”) but no actual practical data showing that it DOES work.
@BMan: I think you and John are actually saying the opposite: he’s saying you need to enhance fat burning to optimize endurance performance, whereas you’re saying you need to enhance glucose burning. Of course, your recommendations on HOW this should be accomplished would probably be very similar! And that, in a way, is why I suggested that we shouldn’t really worry too much about fat-burning in endurance training.
To clarify: I certainly agree that the physiology of fuel utilization is important during endurance performance. There’s no doubt whatsoever that trained endurance athletes burn a higher proportion of fat at a given level of exertion than untrained subjects, and this “carb-sparing” behaviour allows them to go longer/harder before their carb stores are depleted. This is a DESCRIPTION of one of the key adaptations to training.
The question is: can we take this observation and use it to formulate a PRESCRIPTION for how we should train? Many people, of course, have done so. In running circles, it’s very common to emphasize that one should keep the pace on the weekly long run slow, in order to optimally stimulate fat-burning. And the latest “train low” (with depleted glycogen stores) trend is exactly the same thing: trying to train in a way that will deliberately increase fat burning.
My point is that I haven’t seen any evidence that this actually works. It’s easy to say that “in theory it should work,” and maybe it does, but I’m not convinced. Jeukendrup’s belief is (to quote from Amby’s interview):
“I think if the physiological changes are there, the performance must ultimately follow. I think the studies thus far have not been well-enough designed to show the performance improvement, and that includes studies from my lab.”
That may be true. I just think human physiology is sufficiently complicated that observing a physiological change doesn’t guarantee that a PRACTICALLY SIGNIFICANT performance or health change will follow.
@BMan: “I am surprised by Jeukendrup’s statement that the total number of calories burned from fat does not continue to rise past 60% of VO2max.”
I don’t think there’s any reason to doubt this. After all, by the time you hit VO2max pace, you’re essentially burning no fat at all. There has to be a peak somewhere.
(That’s separate from the question of what the optimal intensity is for losing weight. I still believe that — in broad strokes — harder is better, and the number of calories is what matters, since the calories you ingest will simply be stored as fat if you’ve magically managed to avoid depleting your carb stores.)
One other note: I know that, at least until this year, Jeukendrup was a professor at the University of Birmingham. PowerBar funded some of his studies, but had no input on the data or interpretation of the results — and he certainly wasn’t an employee of the company. I don’t know anything about his arrangement with Gatorade, but I wouldn’t be surprised if it’s the same. Of course, I do think it’s very important to understand who funds studies and why — for one thing, it determines not just how questions are answered, but which questions are asked in the first place.
I did not know that was the state of affairs re: fat-burning, that we know why it should work, but that we are not sure that it does. Interesting. Jeukendrup, in a book he edited (which I lent to someone so I can’t be sure if he wrote this section or not) suggests a marathon workout of something like 1hr steady pace, 4x1200m at 5k pace, 1h steady pace, as a “depletion” workout, that is supposed to encourage a higher percentage of fat burning at faster speeds.
@alex: I can accept that there is a point where the total calories from fat does not increase, but I would not expect it to go back down. Why would that system stop working at some point? Obviously I have misunderstood things as I had understood that that system is always working, as is the glucose-burning system, but just one system would be dominant over the other depending on how hard one is going.
I perhaps didn’t read carefully enough about PowerBar, but the article definitely suggests that Jeukendrup is definitely an employee of Gatorade now.
I did misread John’s post. I do not think that one can go very fast for a 2 hour race being in a zone where fat-burning is the dominant fuel source (at least not in swimming anyway). In fact, it seems that, in most cases, the bottleneck is either the burning of glucose fast enough, or the burning of the resulting lactate (depending on who you are… more athletes probably the burning of lactate, but some of the incredible endurance athletes seem to burn lactate incredibly fast).
Obviously the fat-burning needs to be optimal as well because some energy, I assume, comes from that (though given the earlier part of this I feel like I don’t even know anymore if it is significant… though I’m assuming it is). And slower training needs to be done at times for multiple reasons. But I’m not racing at the slower pace and that is not the pace at which I care about being good at burning fat. There are some important benefits gained by training slowly at times, but until there is more evidence I do not believe that.
Lastly, I completely disagree with Jeukendrup’s statement that “if the physiological changes are there, the performance must ultimately follow.” I agree with you Alex that human physiology is far too complex and not well-enough understood to make a statement like that since “the physiological changes” are not defined. Perhaps some physiological markers change, but others, that we may or may not be aware of, may change negatively. And perhaps the markers we read are not always perfect indicators of improved performance. Seems like an odd statement, actually, for a scientist to make.
Hi Alex
Good discussion here. My interest is on the fasted state/glycogen depletion/fat adaptation points. Surprised you don’t think there are any performance gains. I agree that there are no clear cut studies showing improvements in performance measures, as far as I know. However there are several showing improved adaptations. Here’s just one recent one
http://jap.physiology.org/content/110/1/236.short
The “fat burning” argument really has to be taken in context. What constitutes “endurance” can be very different for some people. Improving fat metabolism may not help significantly in a 1 or 2hr event but I think it does come into play when you start going into ultra distance events such as ironman, ultramarathons etc. This sort if endurance has very little research to go on so its very much unchartered territory. However, you just have to look at some of the studies on IMTG, PPAR and IL-6 to see that there are certainly physiological benefits that can improve performance. The direct research just hasn’t been done and I think it is this which Juenkendrup is referring to ?
@Barry:
Thanks for the comments. For sure, if I ever enter a “Who’s got the highest IL-6 levels” competition, I’ll definitely use fasted training to raise my IL-6 levels. 😉
I’m certainly not ruling out the possibility that fasted training could help ultraendurance performance. It seems fairly logical, and there are some encouragingly suggestive studies (including the ones showing “physiological benefits”) — but that’s a pretty low bar to clear. I think we’re highly susceptible to the “Streetlight Effect,” and that leads us to the following sort of faulty logic:
(1) Faster runners have more of Trait X than slower runners.
(2) Technique Y increases Trait X.
(3) Therefore, Technique Y will make me run faster.
Sometimes that’s true, but sometimes it’s not. The way we tell the difference is with performance studies where you employ Technique Y to see if it actually improves performance. So far, glycogen-depleted training hasn’t passed that test, despite several attempts.