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Sweat Science

4 Surprising New Insights on Fueling for Endurance Sports 

The downside of veggies, the upside of emptying your colon, and more


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In sports science, there’s sometimes a disconnect between those who conduct research in laboratories and those who work directly with elite athletes in the field—“at the coalface,” as sports nutritionist Louise Burke puts it. Both groups have valuable perspectives, but I find that the best advice comes from those who manage to straddle both sides of the divide.

On that note, I attended a presentation by Jennifer Sygo at a recent conference in Toronto. Sygo currently serves as a dietitian for the Canadian track and field and gymnastics teams, as well as the Toronto Raptors basketball team. On the side, she’s working towards a PhD at Manchester Metropolitan University, based on her work with the gymnasts. Her talk focused on sports nutrition for endurance athletes, and it included some ideas and perspectives I hadn’t encountered before. Here are a few highlights that stuck with me:

Dial Up the Carbs

I’ll start with the least surprising message from Sygo’s talk: endurance athletes need carbohydrates, and lots of them. She covered the research suggesting that low-carb ketogenic diets don’t improve performance in Olympic-distance endurance events like the marathon, while acknowledging that ultramarathoners might choose to make different trade-offs. Elite marathoners, she pointed out, get about 85 percent of their in-race energy from carbohydrates, with most of that coming from glycogen stored in the muscles and the remainder from glucose in the bloodstream.

To keep those carb reservoirs fully stocked, she shared some specific carbohydrate intake goals she uses with elite runners for various distances:

  • The day before a 10K, fill up your muscles with glycogen by aiming for 7 to 12 grams of carbohydrate per kilogram of bodyweight (g/kg). On race day, take in 1 to 4 g/kg between one and four hours before the race. If you weigh 155 pounds, that works out to between 70 and 280 grams of carbohydrate—a pretty wide range that reflects the individual variation in how well people can handle a meal before exercise. For reference, a breakfast of ⅔ cup of oats, a cup of berries, and a cup of fruit juice gives you 100 grams of carbs.
  • For a half marathon, follow a similar approach, and then—an approach I hadn’t considered—top up your carb stores with a gel or sports drink after your warm-up. She also suggested considering taking in some carbs during the race, or at least rinsing and spitting some sports drink to get the brain benefits. I don’t usually think about in-race nutrition for a race that short, but then again Geoffrey Kamworor drank sports drink at the aid stations when he broke the half-marathon world record a few years ago.
  • For a marathon, increase the pre-race loading to 10 to 12 g/kg for 36 for 48 hours beforehand. That’s an enormous amount, which you’ll probably only achieve by drinking some juice or sports drink in addition to carb-heavy meals. Top up in the morning, and again after your warm-up, and then aim for somewhere between 30 and 90 grams of carbohydrate per hour during the race. (I’ll add that some pro cyclists—and scientists—are now pushing closer to 120 g/hour, but I’m not sure how well that would translate to running.)

Don’t OD on Veggies

Yes, this message surprised me—but read on to see what she meant. One of the big trends in sports nutrition over the past decade has been the idea that, instead of just eating the same things every day, you should adjust your intake to match your expenditures. Sygo showed slides of the Athlete’s Plate, a concept developed at the University of Colorado Colorado Springs along with the U.S. Olympic Committee that offers visual guidance for how you might eat during periods of light, moderate, and heavy training. You can see the three plates here.

On the easy training plate, vegetables and fruits take up half the plate. On the hard training plate, vegetables take up only a quarter of the plate (though fruit has been moved off the plate, since there’s no room for it!). The point isn’t that vegetables are bad. Quite the contrary: they’re essential. But if you’re training hard, your caloric needs are through the roof, and you can’t rely on vegetables alone, or even predominantly vegetables, to get you there. They’re simply not calorie-dense enough, and their high fiber content makes them too filling and laborious to eat.

A common trap, Sygo pointed out, is the “big salad”—a frequent sight when health-conscious endurance athletes gather. You feel like you’re eating an enormous meal, but if you’re not careful it won’t have as many calories as your stomach is telling you. Given the growing understanding of the downsides of (often unintentional) underfueling, it’s worth keeping calorie density in mind. Grains and fats are good options, along with subtler tweaks. For example, the easy training plate includes only fresh fruit; the moderate and hard plates add stewed and dried fruits.

Eliminate Dead Weight

There’s no delicate way to say this: you’ve got one to two pounds of fecal matter in your colon, and getting rid of it before a competition might give you an infinitesimal edge. One approach that athletes in weight-sensitive sports have long used is a temporary low-residue diet—“residue” being the undigested fiber, bacteria, and water that’s left over after you’ve digested the good stuff. In practice, that means cutting way back on fiber for a few days.

Researchers at Liverpool John Moores University in Britain tested this approach in a study published earlier this year. They had 19 volunteers cut back from their typical 30 grams of daily fiber to less than 10 for four straight days, while maintaining the same overall calorie content and macronutrient distribution in each meal. The result: average weight loss of 1.3 pounds, presumably mostly poop. The other result: harder stools and half as many bowel movements, though 18 of 19 volunteers said they’d be willing to repeat the intervention.

There are other reasons you might be interested in a pre-race low-residue diet. A few years ago, pro cyclist Mike Woods told me he follows a “five-year-old’s” low-fiber diet prior to races, not to lose weight but to minimize GI upset. For most of us, losing a pound wouldn’t be worth the hassle. Even for elites, Sygo noted, it’s marginal. She broached the topic with a track athlete recently, but didn’t get far before the athlete cut her off with some version of: I’ll do anything to win, but not that.

Pump Your Iron Up

Sygo isn’t a supplement pusher. She noted four relevant and evidence-backed ergogenic aids for track athletes: beta-alanine, sodium bicarbonate, creatine, and caffeine. Only the last one has been shown to reliably work for long-distance events. (That’s consistent with a recent International Olympic Committee consensus statement, though they also included nitrate on their list.) She also noted some key parameters to monitor on an ongoing basis: vitamin D, vitamin B12—and iron.

The risk of low iron is a familiar topic for endurance athletes. I’ve written before about what thresholds to watch out for and how to get your levels up. Sygo’s target are similar or perhaps a little higher: she suggests aiming for ferritin levels of at least 30 micrograms/L in women and 50 micrograms/L in men. For hemoglobin, she suggests a target of at least 130 g/L for both men and women. The usual minimum threshold for hemoglobin in healthy women is a little lower, but it’s not clear whether that’s really optimal, or just reflects the fact that women tend to have lower (and perhaps suboptimal) hemoglobin levels primarily due to menstruation.

One of the particular challenges for athletes is that heavy exercise produces elevated levels of a hormone called hepcidin, which interferes with iron absorption for up to six hours after training. As a result, Sygo suggests taking supplements away from training time, ideally on an empty stomach, with vitamin C to aid absorption. She also noted a further twist: U.S. Army researchers recently showed that in addition to being triggered by exercise itself, hepcidin is further triggered if you don’t get enough calories to replace what you burn. That’s yet another reason to avoid underfueling.

I should emphasize that I’ve cherry-picked the bits of Sygo’s presentation that I found most interesting or unusual. In practice, it’s the big picture that matters more than the little details. Still, getting your sports nutrition right requires a lot of trial and error, because everyone’s different. You’ll need to experiment to find out which approaches work best for you, and that definitely means rehearsing in training everything you want to try in competition. And in the end, it’s the fundamentals that matter most: eating a healthy, balanced, and calorically sufficient diet is going to do way more for your performance and health than dropping a pound of poop.

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