The New Endurance Fuel
SOME ELITE ATHLETES ARE CONQUERING MILE 50 WITH THE SAME INTENSITY THEY BROUGHT TO MILE 1. THEIR SECRET? FOODS THEY WERE TOLD TO AVOID.
ZZach Bitter, an accomplished endurance athlete, sailed through the initial 35 miles (56km) of his first ultramarathon, the 50-mile North Face Endurance Challenge. He was energised and focused. Fifteen more miles – no sweat, he thought.
But then came hill after hill, and by mile 40, he was running on fumes and losing focus. He rounded a corner, started one more long, brutal climb… and suffered a loss in energy.
He cursed himself and the race route as he staggered into one of the last aid stations. Soft drinks and sports drinks propped him up the rest of the way towards a less-than-smooth finish.
Bitter competed in more ultras, but they always ended the same way: He’d cruise his first 30 to 40 miles, and then inevitably reach a point in the race that left him feeling lightheaded and irritable, and struggling to push forward at an even pace.
In search of a solution, he scrutinised every aspect of his training and nutrition plan. He did research and asked questions. Then he made a radical change: He axed a ton of carbs from his diet, slashed his protein intake, and ate a lot more fat.
After eight weeks on the plan, Bitter’s training intensified and his recovery times fell. In his next race, he didn’t suffer the same fate of his previous ultramarathon and went on to win four ultramarathons in 2012, breaking the US record in 2013 and his own record in 2015.
Bitter’s eating plan – low-carb, high-fat and moderate protein – is called a ketogenic diet. It’s not for the faint of heart, and even though it goes against years of “carbs are king” endurance dogma, it’s gaining traction with some elite endurance athletes, who say it helps them go harder for longer and feel just as good on their 50th mile as they did on their first. How could such a counterintuitive plan possibly work?
Like this: With a typical diet, your body converts glucose (a type of sugar) from the carbs you eat into glycogen. That glycogen is stored in your liver and muscles, where it’s a fast fuel for hard exercise. Unfortunately, however, your body can store only enough glycogen for around two hours of intense exercise.
If you do only short events, that’s fine. But if you’re a distance junkie, it’s a problem. Once you hit hour 2 without refueling, your glycogen stores are tapped and your body searches for energy elsewhere. Finding nothing, it crashes.
To prevent this, you pound gels, drinks and energy bars as you run, ride or swim to keep glycogen stores high. Eating enough carbs to thwart a sudden loss of energy during an endurance event is impractical if not impossible.
The ketogenic diet works by replacing carbohydrates with fat as the primary fuel source. When you shun carbs and limit protein, your body enters a state called ketosis. Eventually it becomes “fat adapted” and resorts to running on fat instead of sugars.
That’s ideal for long endurance events where access to food is a limiting factor because once your body is done burning the fat you eat, it starts to burn the fat on your frame. Even if you’re lean, you have enough body fat to fuel nearly any distance race, which is why you won’t lose energy suddenly.
When a triathlete limits carbs and protein, the body learns to power itself on fat, not sugar.
“At a very high level, where the smallest edge can mean victory, I’d bet on a ketogenic endurance athlete,” says Men’s Health nutrition advisor Mike Roussell.
The catch: The diet is demanding. About 80 percent of your calories come from fat, 15 percent from protein, and as little as 5 percent from carbs. If you eat 2,500 calories a day, that’s 220g of fat, 90g of protein and 40g of carbs. That’s a lot of eggs, butter, avocados and nuts. And you have to eat like this for weeks.
While your body can become fully adapted to burning fat as fuel in four weeks, Roussell advises endurance athletes to follow the diet for eight weeks or longer before competing.
According to Roussell, no credible science opposes the diet from a health perspective. However, not everyone’s biochemistry is suited for ketosis.
When you’re first forcing your body into ketosis, you might come down with “keto flu,” with symptoms that include fatigue, brain fog and possibly irritability. And if you follow the diet haphazardly, you may become deficient in certain nutrients. Unless you’re chasing epic distance, this may be more trouble than it’s worth, and some scientists are still skeptical.
“I haven’t yet seen evidence that the ketogenic diet provides a superior approach,” says Louise Burke of the Australian Sports Commission.
But some athletes swear by it. “I believe a ketogenic diet has allowed me to train harder,” Bitter says. Since he started using the keto diet, he says he hasn’t had that “emotional roller coaster” feeling where his body feels like it’s shutting down on him.
For endurance athletes, that’s the difference between suffering from sudden fatigue and energy loss and breaking the tape.