Editor’s Note: The referenced study has been summarized to include salient details for the sake of brevity. Click on the study to read in detail if you wish. It should also be said that no one diet is best for everyone and results may vary.
The sport of mountain biking is not often praised for its simplicity. To ride, you first need a bike. Then a helmet and the right shoes. So you have to take your bike to the trailhead. Oh, and don’t forget the water and snacks. You don’t want to fuck after all!
Usually, the snacks we carry or find in bike shops are high in carbohydrates, as the macronutrient is our preferred source of energy. Carbohydrates are more easily broken down in the body and converted into energy. The longer the trip, the more likely we are to deplete our stores of glucose and glycogen (converted carbohydrates that are stored in the liver and muscles), forcing us to eat more carbohydrates to keep going. It’s a vicious circle if ever there was one.
The keto diet (short for ketogenic) has been around for a century, dating from the 1920s when doctors introduced it as a treatment for epilepsy. As anti-epileptic drugs became available over time, the ketogenic diet died out as a method of treatment. Since then, athletes and dieters have revived it for other reasons. In recent years, the popularity of the ketogenic diet has skyrocketed, sparking interest in the low-carb, high-fat, high-protein diet.
The premise behind the ketogenic diet is that as dieters transition from carbohydrates to higher protein and higher fat foods, the body adapts more to fats and instead uses glucose or glycogen As a limited energy source that needs to be fueled frequently, we can dip into our vast reserves of body fat.
As cyclists, the practicality of Keto sounds pretty good, if not outright advantageous; less sex, less food to pack for a trip, and more fat burning and weight loss. To find out a little more, I dug into some recent research and spoke with an extraordinary resistance trainer. Hunter Allen from Peaks Coaching.
Endurance athletes take on the ketogenic diet
TO published study in the Journal of the International Society of Sports Nutrition used a small sample of five endurance athletes to study the effects of the ketogenic diet on performance over ten weeks. Athletes participated in performance tests such as time to exhaustion, peak power and VO2 max tests. Participants were instructed to eat less than 50 g of carbohydrate per day, 1.5 g of protein per kg of body weight, and “fat ad libitum”, or as much as they wanted. For reference, a cup of rice it has about 45 g of carbohydrates.
The study reported that the athletes experienced reduced energy levels shortly after cutting out carbohydrates.
Harvard Health Publishing Reports that the “keto flu” is a common set of symptoms that new keto dieters often experience in the form of headaches, irritability, nausea, or difficulty sleeping as they reduce their carbohydrate intake.
After these feelings faded, the athletes’ energy returned and they were able to exercise at a high level again, but felt they couldn’t do high-intensity exercises as easily.
The athletes underwent ketosis, where their body converts fat to ketones for usable energy, at the end of the second week, and they were instructed to measure their blood ketone levels daily.
At the end of the ten-week study, the athletes shared similar results. They had a better sense of well-being and reduced their body fat and weight. Even though they ate fatty foods, the researchers attributed the weight loss to a calorie deficit. Participants ate less on keto and felt more full on foods high in fat and protein. People tend to lose water weight quickly after eating fewer carbohydrates as well.
Sports performance was a bit more complicated. “The performance decline in our study and others is likely due to changes in metabolic pathways that affect glycogen metabolism at higher exercise intensities.” In other words, it appears that the study suggests that as exercise intensity increases, it becomes difficult for the body to function without glucose or glycogen and your body’s ability to utilize carbohydrates on keto at higher intensities may be inhibited for a period.
In practice
Hunter Allen with Peaks Coaching has seen similar experiences in the athletes he has coached. Allen has had five to 10 athletes he has worked with in the past who have tried ketogenic diets. All of them had a difficult transition from traditionally high-carb endurance diets to almost no carbs.
“All cyclists have been through the same thing,” Allen said. “A two-week transition period where they feel like shit, they don’t have a lot of energy, their body goes through this kind of ‘what are you doing to me?’, and then at the end of the two-week phase where They start to feel better.”
He said the actual transition can take 4-6 weeks or even longer to really adjust to the fat. The reasons his athletes experimented with the diet included weight loss, more stable blood sugar levels, and higher energy levels.
For low-to-moderate intensity exercise, Allen said the ketogenic diet tends to work very well. As people increase exercise intensity and reach the medium or high pace phase of Coggan Power Level Chartor 85-90% of their functional power threshold – your maximum power output for one hour in watts – it becomes more difficult to operate in ketosis.
“When we start reaching higher intensity levels in tempo and above, that’s where we really start to use glycogen and blood sugar as energy sources,” Allen said. “If you’re highly trained to burn fat, there are some really amazing athletes who can burn fat at around 80% of their FTP, which is maybe the maximum intensity for fat burning, but more research needs to be done to be sure. Well above 80%, almost everyone begins to transition to burning glycogen, or using sugars found in the bloodstream. That’s where the ketogenic diet starts to slip.” Even for fat-adapted athletes, it is more difficult to exercise at high intensities without immediate access to glucose or glycogen in the blood.”
life after keto
All of the keto athletes Allen has worked with eventually returned to a more balanced carbohydrate diet for various reasons. Either they lost the desired amount of fat or they needed to move from an aerobic-based phase to a training program that required high-intensity exercise and needed more carbohydrates to perform. Still, many of them reduced the amount of carbohydrates they normally ate and seemed to realize that they may have been eating too many carbohydrates before keto.
“To me, endurance cyclists are very carb-addicted,” Allen said. “We use a lot of carbohydrates. We eat a lot of carbohydrates and I think [we] probably eat too much. And I think a lot of us [endurance athletes] it would benefit from being more fat-adapted and having a lower percentage of carbohydrates. We need enough carbs so you can recover and do your intense workouts, so it makes sense on those days when you really need it, eat carbs.”
Allen mentioned that he often uses fat-fitting programs for professional American cyclists who move to Europe to compete, since the tours are often longer. If they can adapt more to fat, they can go a longer portion of the race without fueling up and start using carbohydrate sources midway through the race.
Still, for most of us, losing weight comes down to math, Allen said. There are 3,500 calories in a pound of fat. Eat 500 fewer calories per day and that puts someone on track to lose a pound in a week. “If you want to lose weight, for me it’s purely a mathematical equation.”
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