Keto Fuel Endurance Exercises? Don’t You Need Carbs?
This isn’t the first time someone has asked these questions. In fact, a researcher named Stephen Feeney asked the question in the early 1980s, around the time that The Empire Strikes Back (the second Star Wars movie) was released.
We’ll discuss his experiment shortly, as the results are useful for keto dieters interested in health. But before that, we’ll cover the potential adaptation caused when ketones switch to fat as a fuel.
Therefore, whether you are a cyclist, jogger, swimmer, hiker, football player, or any type of weekend warrior, you will find something useful in the final installment of our Keto Workout Series.
What are endurance sports?
Endurance exercise, or endurance training, generally refers to activities that increase aerobic capacity. Aerobic capacity, also known as cardiorespiratory fitness, represents the maximum amount of oxygen you can consume during physical activity.
This is measured as VO2 max, which is your maximum oxygen consumption during vigorous exercise. The higher your VO2 max, the more aerobic you are considered to be.
By now, you might be wondering how the ketogenic diet affects VO2 max. The short answer is: probably not much.
However, VO2 max is not the only important indicator of endurance training. For example, it doesn’t tell you about actual performance or fat burning.
We’ll be there soon.
How do you promote endurance sports?
In order to promote muscle contraction during exercise, you need energy. This energy comes in the form of a molecule called adenosine triphosphate or ATP.
ATP is available energy. To make ATP, your body (mainly) uses any of the following:
1.carbohydrate
2.fat
The main determinant of which fuel to use? The availability of carbohydrates.
When carbohydrates are available, your body preferentially uses them (glucose) to make ATP. When they are not available, you turn to fat for energy.
Due to the scarcity of carbohydrates in the keto diet, it has triggered a shift towards fat as fuel. This not only allows you to burn more fat, but also unlocks large fuel reserves that were previously unavailable.
The name of this process is? Keto adaptation.
ketone adaptation
Ketone adaptation, also known as fat adaptation, refers to the transition from carbohydrates to fat as a primary energy source. Based on available evidence, ketone adaptation can take anywhere from 2 to 8 weeks, depending on your metabolism.
So let’s talk about how endurance sports typically refuel. If you’re familiar with ultra-endurance sports — marathons, long-distance swims, triathlons and so on — you know that in these endeavors, athletes need a constant supply of carbs.
Why? Because your body can only store a limited amount of carbohydrates — about 500 grams for glycogen in muscle and liver cells. That’s only 2,000 calorie.
Apparently, 2,000 calorie won’t get you through a marathon. That’s why ultra-endurance athletes drink that sugary slime. They need extra energy.
But if an athlete gets used to ketones, she can get a richer source of energy: body fat. Body fat contains about 20 times more calorie than glycogen, even in lean people.
To sum up: Carbohydrate tanks can hold 2,000 calorie, while fat tanks can hold nearly 40,000 calorie. Having access to fat tanks seems to have a big advantage.
But will this advantage translate into the real world of endurance sports?
Ketones for endurance training
In 1980, world-renowned ketone researcher Stephen Feeney conducted an interesting experiment in which he tested the endurance of six obese people (on a treadmill) under two different conditions:
1.A normal carbohydrate diet
2.protein-supplemented (low calorie ketogenic diet)
The results were not subtle. After six weeks of keto acclimatization, participants were able to stay on the treadmill for nearly twice as long before becoming exhausted!
In another study in 1983, this time on cyclists, Feeney found that after four weeks of fat acclimatization, cyclists burned significantly more fat without any damage to VO2 max.
Since then, more evidence has emerged that ketones are compatible with endurance training.
After two weeks of high-fat dieting, trained cyclists improved fatigue time during moderate-intensity exercise
Many ultra-endurance runners succeed on the keto diet – burning more body fat for energy over long periods of effort
Based on these studies, the main benefits of keto adaptation are increased fat burning and increased fatigue time. This makes sense. The fat tank is much larger, so you can work harder for longer when keto fuel is plentiful.
What about other performance indicators? The jury is still out. For example, one study of elite race walkers found that although they burned more fat on a low-carb diet, they needed more oxygen to fuel the same amount of exercise – not a positive sign.
Recovering from a ketone workout
Can you recover from exercise without gaining weight? To answer this question, let’s examine two recovery indicators: lactate and glycogen.
1: Lactate
During exercise, you form a compound called lactic acid as an alternative fuel source. After exercise, excess lactic acid is cleared by the liver.
However, trying harder and longer causes lactic acid to accumulate faster than it clears. The more lactic acid accumulates, the more damage to recovery.
Where is the role of ketones? In a 2014 study, a one-month ketone diet increased cyclists’ lactate threshold. In other words, they could clear lactate more effectively at higher intensities.
In another study, ketogenic endurance athletes had lower lactate concentrations after exercise than carbohydrate-fed athletes. This suggests better recovery.
2: glycogen
Keto adaptation doesn’t mean you use zero carbs for energy. Harder, longer workouts always require some glucose. But in keto adaptation athletes, the balance shifts from carbs to fat.
That’s where glycogen comes from. If you remember, glycogen is your body’s carbohydrate storage tank. The more glycogen you use during exercise, the more fatigue you get.
By reducing the need for glucose, ketones may reduce the need for glycogen. This will allow the ketone-adapted athlete to save his carbohydrate tank and avoid fatigue. [*]
Ketones for Endurance Exercise: The Bottom Line
Fat can boost endurance exercise as much as a carbohydrate diet if given enough time to adjust to ketones. Several studies have shown that fat burning and fatigue time improve when people adapt to ketones.
However, this doesn’t mean that ketones improve all aspects of endurance performance. Depending on the metrics you see, it may not.
To train keto endurance, allow 4-6 weeks of keto to adapt to a low-carb diet. This trains your body to burn more fat during exercise and requires fewer carbs.
Finally, listen to your body. Not everyone feels their best during keto training, and you may want to bring back carbs. For specific strategies on carb cycling, exercise logs, and more, check out Carb Manager’s Keto Workout Guide, and our in-depth look at the Circulating Ketogenic Diet. Thanks for reading, happy training.
