Why endurance athletes are cutting carbs more than ever

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After the 2022 Tour of Flanders, a photo went viral on social media showing a detailed nutrition plan carefully taped to the handlebars of race winner Mathieu van der Poels. The rough math showed that the Dutchman had cut well over 100 grams of carbs per hour while completing the 169-mile race in just over six hours, a remarkable feat for digestive studies given that conventional sports nutrition guidelines dictate that our ability to absorb carbohydrates is at its peak. about 90 grams per hour.

To outsiders, van der Poels’ megacarbohydrate intake seemed like a separate novelty. But in the year and a half since then, very high carb doses have become an emerging trend among elite endurance athletes. New science suggests that it’s actually possible to consume up to 120 grams of carbs per hour, and some experts say even higher. The unanswered question for now is whether it will make you faster.

The latest study on the matter has just been published Journal of Applied Physiology a research team led by Robert Jacobs of the University of Colorado Colorado Springs. Jacobs and his colleagues use real data to simulate the physiological characteristics of elite marathon runners and calculate how much carbohydrate they would need to successfully run a marathon under two hours.

If you’re fit, lean, and high in carbs, you’ll already have a significant amount of carbs when you start a marathon, mainly as glycogen in your liver and muscles. The exact amounts depend on several factors, including liver and leg size, but on average, researchers estimate that elite male marathoners start with 690 grams of glycogen and female marathoners with 499 grams.

At first glance this seems promising, as they calculate that a two-hour marathon should require 612 grams of carbohydrate for elite men and (since women are smaller on average) 528 grams for women. The problem is that you cannot empty the tank completely for several reasons. One is that running doesn’t use all the leg muscles equally, so the underused muscle fibers still have stored glycogen when you hit the wall. Overall, you can use about 62 percent of your stored carbohydrates during a two-hour marathon, leaving a significant deficit that you must fill by drinking or eating more carbohydrates.

To make the numbers work for a two-hour marathon, Jacobs and his colleagues calculate that the average elite male marathoner would need to consume 93 grams of carbohydrate per hour, while the average female would need 108 grams per hour, which is significantly more than 90 grams. gram max according to current sports nutrition guidelines.

This is an interesting analysis, although it must be recognized that it puts the cart (what wed Like run) before the horse (which I was really capable of). We could perform a similar calculation of how many carbs we need to run back-to-back marathons in four hours, and that calculation would yield an astronomically high number, but the number would have no real meaning. Endurance limits depend on a lot more than carbohydrate intake.

Still, Jacobs offers three arguments for why two-hour marathon numbers should be taken seriously. One is that recent laboratory studies have shown that humans can actually burn more than 90 grams of exogenous carbohydrates (meaning drinks or food rather than internal storage) per hour. For example, a study published last year by Tim Podlogar, an exercise physiologist at the University of Birmingham and nutritionist for the Bora-Hansgrohe pro cycling team, fed cyclists 120 grams of carbohydrate per hour and found that they were able to burn just over 90 of those grams per hour. (The rest is either excreted or stored for later use.) Achieving this level of carbohydrate burning meant drinking a 1:0.8 mixture of glucose and fructose, a change from the usual 1:0.5 ratio in many current sports drinks and gels.

Another argument is that the digestive system can adapt. Sure, if you try to feed volunteers 120 grams of carbohydrate per hour, their stomachs will rebel and you’ll conclude that it’s impossible to absorb that much. But try abs training for a few months like the Mathieu van der Poels of the world have done, and who knows what you’ll be up to?

The third claim is anecdotal: many very fast athletes in sports such as cycling, triathlon and running exceed 90 grams per hour. Velos Jim Cotton had a fascinating article in October about the carb revolution in cycling. There has been a huge change in energy intake in the last five or six years, Ineos Grenadiers nutritionist Aitor Viribay Morales told Cotton. It’s one of the biggest reasons why cyclists produce so much power for so long and how they produce it every day.

So let’s agree that moving the goalposts from 90 grams to 120 grams per minute is plausible. But you should be careful before jumping on the bandwagon. First, elite endurance athletes can burn carbohydrates faster and much longer than the rest of us. One of the reasons that previous studies concluded that humans could not smoke more than 90 grams per hour is probably because the subjects were only well-educated and not elite.

Even if you can absorb 120 grams per hour, it doesn’t necessarily make you faster. In Podlogars study, cyclists smoked more exogenous carbs when they ate 120 grams instead of 90 grams per hour, but it didn’t reduce their endogenous the burning of carbohydrates, i.e. they had continued to deplete their muscle glycogen stores just as quickly. Other studies have found the same effect, and a few studies have even shown that higher carb consumption actually inhibits fat burning so effectively that you end up burning through your internal carb stores faster than otherwise, which is just the opposite. of what you wish for.

As it happens, Medicine and science in sports and exercise has just published an academic discussion they call Contrasting Perspectives on whether ketogenic diets are beneficial for athletic performance. The pro-keto case is argued by Tim Noakes; argue Louise Burke and Jamie Whitfield of the Australian Catholic University, who led a series of studies on ketogenic diets in elite race walkers. I wrote about some of Burke and Whitfield’s results here, and I’m not going to rehash the whole discussion. My overall view remains the same as it was then: keto for endurance is a great idea in theory, but when you actually test performance, it doesn’t live up to the hype.

Interestingly, despite the headline, ketogenic diets benefit athletic performance. The Noakess pro-keto case doesn’t spend much time arguing that ketogenic diets improve performance. Instead, he focuses on a slightly different argument: contrary to conventional wisdom, adding carbs during exercise won’t make you faster. In short, he argues that the only benefit of consuming carbohydrates during exercise is that it keeps your blood sugar high enough to fuel your brain, which would otherwise leave you feeling deeply fatigued. This would explain why many studies have seen performance benefits from sports drinks, even though Podlogar and others have found that super high carb doses don’t actually extend internal carb stores. To keep blood sugar high, Noakes characterswould only require 20 grams of carbohydrate per hour regardless of whether you normally eat a low-fat or high-fat diet.

So should we increase our carb intake to 120 or above or return it to 20? The honest answer at this point is that both ideas are speculative. The world of extreme endurance sports is voting with its feet (or maybe going internally) for carbohydrate mania. I guess they’re right, assuming your primary interest is winning races in the Olympics. But we have to keep in mind that no one has proven that 120 grams per hour makes you faster than 90, and even a 90 over 60 case is not watertight. The only way to resolve the dispute is to gain more information from well-designed trials or, in the meantime, like Mathieu van der Poel, by winning races.

For more Sweat Science, join me on Threads and Facebook, sign up for the Email Newsletter, and check out my book Enduring: the mind, the body, and the strangely flexible limits of human performance.

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