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teaser
Wed, Nov-18-15, 06:40
http://www.sciencedaily.com/releases/2015/11/151117091234.htm

Endurance athletes who 'go against the grain' become incredible fat-burners
Elite performance on a diet with minimal carbs represents a paradigm shift in sports nutrition

Elite endurance athletes who eat very few carbohydrates burned more than twice as much fat as high-carb athletes during maximum exertion and prolonged exercise in a new study -- the highest fat-burning rates under these conditions ever seen by researchers.

The study, the first to profile elite athletes habitually eating very low-carbohydrate diets, involved 20 ultra-endurance runners age 21-45 who were top competitors in running events of 50 kilometers (31 miles) or more.

"These low-carb athletes were spectacular fat burners," said lead researcher Jeff Volek, professor of human sciences at The Ohio State University. "Their peak fat burning and the amount of fat burned while running for three hours on a treadmill was dramatically higher than what the high-carb athletes were able to burn.

"This represents a real paradigm shift in sports nutrition, and I don't use that term lightly," he said. "Maybe we've got it all backwards and we need to re-examine everything we've been telling athletes for the last 40 years about loading up on carbs. Clearly it's not as straightforward as we used to think."

The 10 low-carb athletes ate a diet consisting of 10 percent carbs, 19 percent protein and 70 percent fat. Ten high-carb athletes got more than half their calories from carbs, with a ratio of 59 percent carbs, 14 percent protein and 25 percent fat.

In all other respects, the athletes were similar: elite status, age, performance, training history and maximum oxygen capacity. "They all had the same engine, so to speak," Volek said.

Scientists measured gas exchange repeatedly during a test determining the athletes' maximum oxygen intake to gauge carb- and fat-burning rates. On average, the low-carb runners' peak fat-burning rate was 2.3-fold higher than the rate for high-carb athletes: 1.5 versus .67 grams per minute.

The research is published online in the journal Metabolism: Clinical and Experimental.

Volek has been studying the effects of low-carb eating -- and ketogenic diets specifically -- for years, particularly in the context of obesity and diabetes. But he has always been interested in how such a diet might augment physical performance and recovery. Ketogenic diets are those that reduce carbohydrates enough to allow the body to access its fat stores as the primary source of fuel. Lowering carbs and increasing fat intake leads to the conversion of fat into ketones, molecules that can be used by cells throughout the body, especially the brain, as an alternative to glucose.

It can take weeks or longer for the human body to fully adjust to a ketogenic diet, so the low-carb athletes in the study were eligible only if they had been restricting carbs for at least six months. Their average time on a ketogenic diet was 20 months.

"The goal was to characterize their metabolic response to a standardized exercise test," Volek said. "This is the first time we've had the opportunity to peek under the hood at what a long-term low-carb, fat-adapted athlete looks like."

Over two days, researchers subjected the athletes to tests to determine peak fat burning during a brief high-intensity workout and metabolic characteristics during prolonged exercise.

On day one, the athletes ran on a treadmill to determine their maximum oxygen consumption and peak fat-burning rates. On day two, the athletes ran on a treadmill for three hours at an intensity equal to 64 percent of their maximum oxygen capacity. During this test, they drank water but took in no nutrition -- before the run, athletes consumed either low- or high-carb nutrition shakes consisting of about 340 calories.

During the endurance run, the two groups did not differ significantly in oxygen consumption, ratings of perceived exertion or calorie expenditure. However, fat-burning rates during prolonged exercise were again about twice as high in the low-carb athletes, and the average contribution of fat during exercise in the low-carb and high-carb groups was 88 percent and 56 percent, respectively.

"The low-carb guys go beyond what you can achieve with good genetics and extensive training," Volek said. "The high-carb runners were very healthy, and were awesome fat burners by conventional standards -- yet their peak fat burning is less than half that of endurance athletes eating low-carb diets. This shows that we have far underestimated how much fat humans can burn. There is a large reserve capacity that can only be tapped if carbs are restricted.

"So far, this has been a grassroots movement. Athletes on their own have been going against the grain, so to speak, and experiencing a lot of success. I think it's mainly taken off in the ultra-endurance world because the self-perceived benefits are so high there, but many other athletes competing in a variety of events and various sports teams are experimenting with carb restricting," Volek said.

Another key finding: Despite their low intake of carbs, these fat-burning athletes had normal muscle glycogen levels -- the storage form of carbohydrates -- at rest. They also broke down roughly the same level of glycogen as the high-carb runners during the long run, and synthesized the same amount of glycogen in their muscles during recovery as the high-carb athletes.

"This was completely unexpected, but now that we have observed it we have some novel ideas why this is the case. We can only speculate on the mechanism behind it," Volek said.

Muscle glycogen was discovered in the 1960s to be a critical energy source for athletes, which led to decades of emphasis on high-carb diets to support energy needs during intense exercise. But Volek said the body has an elegant system to support glycogen levels even when carbohydrates are limited in the diet.

"The blue print for becoming 'fat- or keto-adapted' is hard wired into our genetic code. However, traditional 'healthy' diets with carbohydrates as the dominant nutrient prevent this alternative metabolic operating system from ever booting up.

"Restricting carbs allows the program to reboot and enable many athletes to achieve improved levels of health and performance" he said.



The study itself is open access.

http://www.metabolismjournal.com/article/S0026-0495(15)00334-0/abstract

The bit about glycogen is interesting. From earlier talks by Phinney and Volek, I would have expected the low carb group to have conserved their glycogen during the run. The usual scenario described was that burning more fat, keto runners would conserve glycogen, the suggestion was that what would happen is that they'd begin the race with lower glycogen levels, due to their diet, but would deplete glycogen more slowly, making them less likely to bonk by the end of the race. Now I'm not sure if this was based on actual data or extrapolation... they had less data points to work from, but I know they had some data on endurance athletes on a keto diet having a higher peak fat oxidation than high carb athletes. And in short term studies, certainly people on a low carb diet will have lower glycogen levels... put the two together, and the "usual scenario" seems like a reasonable hypothesis.

But maybe we gain something, where we lost something. The bonk-proofing of a ketogenic diet was supposed to work because glycogen was preserved--an unfortunate corrollary of that was that maximal effort was supposed to be compromised. Maybe it's not so compromised. These athletes were able to dip into their glycogen as necessary, just fine--and their maximal fat burning was quite high. The glycogen actually measured in the study was muscle glycogen, liver glycogen might have been a different story.

The test was 65 % of VO2 max for a three-hour treadmill run--it would be interesting to see differences in actual distance run.

Other studies have shown
that a low-carbohydrate/high-fat diet decreases resting glycogen and the rate of glycogen use
during submaximal exercise (25,26). The duration of the LC diet was shorter (4 wk) in the work
by Phinney (10), suggesting that complete adaptations in glycogen homeostasis and kinetics may
take several months. The different glycogen responses could also be due to lower carbohydrate
intake, which was <10 g/day in cyclists (10) versus 86 g/day in the LC runners. A short-term
glycogen loading effect is unlikely since food logs were recorded for the two days leading up to
testing and indicated the average carbohydrate intake was 64 g/day in LC athletes
(Supplemental Table 1). The small relative contribution of carbohydrate to energy expenditure
in LC athletes, but similar use of glycogen as HC athletes, indicates a decreased reliance on
circulating glucose in the keto-adapted athlete.

Okay, there was a somewhat higher carbohydrate intake than in the studies showing a different glycogen response. This is in the range that Ben Greenfield was in when he was doing keto, he was around a hundred grams of carbohydrate a day if I remember right.

GRB5111
Wed, Nov-18-15, 09:58
We're now starting to get some excellent information from Volek and Phinney regarding how the body produces and accesses glycogen under stress. Thanks for this link, teaser. I'd love to see the same metrics tracked over the course of an ultra marathon, and to your point, tracking liver glycogen in subsequent experiments would also be valuable. Fat burning for humans is part of our DNA, and if we can peg the optimum WOE to take advantage of this metabolic functioning, it's very likely to result in the most healthy WOE for the individual. This is the way our bodies should work. Looking forward to more of these studies.

jschwab
Wed, Nov-18-15, 10:32
Chris McDougall's new book Natural Born Heroes explores this phenomenon, among other things, in a very entertaining way.

M Levac
Wed, Nov-18-15, 17:34
Another key finding: Despite their low intake of carbs, these fat-burning athletes had normal muscle glycogen levels -- the storage form of carbohydrates -- at rest. They also broke down roughly the same level of glycogen as the high-carb runners during the long run, and synthesized the same amount of glycogen in their muscles during recovery as the high-carb athletes.

"This was completely unexpected, but now that we have observed it we have some novel ideas why this is the case. We can only speculate on the mechanism behind it," Volek said.

Muscle glycogen was discovered in the 1960s to be a critical energy source for athletes, which led to decades of emphasis on high-carb diets to support energy needs during intense exercise. But Volek said the body has an elegant system to support glycogen levels even when carbohydrates are limited in the diet.
So they had it wrong. For the last 50 years. That's a very long time to stay wrong, especially for scientists.

Sorry, I'm going to be a bit off topic here. As I was thinking about this experiment and their results, it occurred to me to search for info on the effect of dietary carbs on IDE (insulin-degrading enzyme), specifically the PPAR pathways, if it exists. If it does exist, it can explain what we call insulin resistance. Additionally, dietary fat activates the PPAR pathways in the liver. My point is that dietary fat has the potential to maintain insulin sensitivity, while dietary carbs have the potential to cause and maintain insulin resistance, both through the same PPAR pathways in the liver. That's the idea anyway. Besides the obvious direct effects we all know about - BG level, insulin secretion, inhibition of ketogenesis, etc - if there's also an effect on IDE through PPAR, we can explain it more thoroughly.

Thanks for posting the article, Teaser.

M Levac
Wed, Nov-18-15, 17:48
When more fat is released from fat tissue, more glycerol is also invariably released from the same fat tissue. This glycerol can certainly be used to make new glucose, then stored as glycogen. If we also believe cells require a specific substrate ratio for optimal function, and if this ratio can be had just from the inherent ratio in triglycerides, then it easily explains why there's no problem whatsoever in maintaining glycogen level on a VLC diet.

I think there's a problem with the idea of "maintaining glycogen level". To me, it sounds like "maintaining triglycerides level" in fat tissue, cuz glycogen is the storage form of glucose, just like triglycerides is the storage form of FFAs. I'd be more focused on conversion rate instead. Even if glycogen level is kept higher on a high-carb diet - which is basically the goal of carb loading - the dietary carbs also keep insulin higher, and insulin inhibits glycogenolysis. In fact, that's how glycogen level is kept higher. If I focus on conversion rate, then it's obvious that if dietary carbs keep insulin higher, and if insulin inhibits glycogenolysis, then this conversion will inevitably be lower than otherwise, which is totally not what we want for optimal performance. Conversely, if dietary carbs are almost absent, insulin is kept lower, glycogenolysis is less inhibited (the conversion rate is higher), we get more glucose from that. But apparently it makes no difference to the actual glycogen level, it stays the same either way. This implies that conversion rate is higher in both directions on VLC diet. However, it does not imply that oxidation rate is higher for glucose on VLC. It's not, it's invariably lower, while lipid oxidation is higher, therefore fat tissue de-esterification (breakdown of triglycerides into FFAs and glycerol, i.e. conversion rate) must also be higher.

M Levac
Wed, Nov-18-15, 18:21
They focused on getting more glycogen for 50 years. Carb loading is the norm. Imagine if they'd discovered something different, say, that triglycerides inside fat tissue were "a critical energy source for athletes". Somehow, I doubt they'd have tried to get more fat, or if they had they'd have soon found out an extra 10lbs of fat ain't so good for optimal performance. Cuz basically that's what they're doing when they're carb loadin, they're trying to grow more glycogenous. Since glycogen is measured not in lbs but in grams, it's very hard to immediately notice the mistake when there's too much of it. I mean, if there's too much of it, the only way that's possible is if insulin is too high, and insulin inhibits glycogenolysis, the very thing that makes this glucose available. With fat tissue, it's exactly the same hormone and the same principle, but with fat tissue, we also have to deal with a very significant amount of extra mass. This extra mass is a problem in itself, once fixed, the conversion problem is fixed too. Rather, in order to fix the mass problem, we must fix the conversion problem first, because the mass problem is created by the conversion problem.

GRB5111
Thu, Nov-19-15, 08:56
When more fat is released from fat tissue, more glycerol is also invariably released from the same fat tissue. This glycerol can certainly be used to make new glucose, then stored as glycogen. If we also believe cells require a specific substrate ratio for optimal function, and if this ratio can be had just from the inherent ratio in triglycerides, then it easily explains why there's no problem whatsoever in maintaining glycogen level on a VLC diet.

Bingo! This is the key and has obviously escaped or been ignored by the "experts" over the past many years. The glyceral component contributes to glycogen production, so it's obvious why glycogen stores in LC endurance athletes are at the same levels as the HC athletes. The significance with Volek's and Phinney's studies is that LC endurance athletes have an advantage due to their ability to conserve and access this energy over a longer time period resulting in increased endurance capability.