Why Endurance Athletes Should Go Keto

Why Every Endurance Athlete Should Go Keto

Dietary ketosis or “keto” is becoming more popular. It is a strategy everyone is asking about. Ketosis or a ketogenic is a process where your body learns to burn fat as its primary source of fuel. This process is called fat adaptation. Fat adaptation offers everything an endurance athlete could dream of. It provides endless energy. This means no bonking. It is also an efficient pathway to weight loss. The diet has been all over mainstream magazines. It’s the subject of several new books. Is it time for cyclists, triathletes, and runners to go Keto? …I say YES, but you can decide for yourself.

What is a Ketogenic Diet?

First, a refresher course on what a ketogenic diet is. It is a diet where your body produces ketones. This requires you to lower your carbohydrate levels. Some people make ketones with 200+ grams of carbohydrates per day. Others need to limit carbs to less than 20 grams per day. Insulin and glucagon levels determine when the body makes ketones. It doesn’t really matter what the number is, it matters that you find the level where your body is making ketones.

What is Ketosis?

What is ketosis anyway? In human beings and most other mammals, acetyl-CoA formed in the liver during the oxidation of fatty acids (a.k.a. turns fat into fuel). They may enter the citric acid cycle or it may be converted to the “ketone bodies”. The ketone bodies are acetoacetate, D-β-hydroxybutyrate, and acetone. Acetoacetate and D-β-hydroxybutyrate are transported by the blood to the tissues. This is where they are oxidized to provide the energy required by tissues. The brain uses acetoacetate and/or D-β-hydroxybutyrate.

 It is a pretty handy process. The very leanest athlete has about 40,000 calories of fat on board as fuel. This is about 20 times the amount of energy stored in the form of fat than it does as a carbohydrate.  

What Happens When Your Body Does Not Make Ketones?

Many endurance athletes are able to perform at a high level but are unhealthy. Dr’s Phil Maffetone and Paul Laursen highlight the issues with many endurance athletes in their article Athletes: Fit but Unhealthy?“. Athletes become unhealthy because of their overuse of carbohydrates. The best way to ensure you maintain your health as an athlete is to increase your fat burning. Increasing your ketone levels and fat oxidation rates is like buying health insurance. You are ensuring you maintain your health while you make performance gains.

Problems with Blood Sugar

Not being able to tap into your fat stores results in hypoglycemia.  The body’s ability to regulate energy is dependent on a regular supply of carbohydrates. If you don’t manage this well you become hypoglycemic.  The ill effects of hypoglycemia are clumsiness, trouble talking, confusion, loss of consciousness, and sometimes seizure. Coupled with the feeling of hunger, sweating, shakiness, and weakness. Wow, that sounds pretty horrible. Before I switched to keto, this was me and I hated it. I would eat a meal and feel like I could slip into a coma afterward. I imagine if you have ever felt hypoglycemia, you don’t want to go there either. When your body uses ketones for fuel you will never have to worry about having hypoglycemia ever again.

Problems with GI Distress

A second reason a ketogenic diet is beneficial is that it prevents gastric distress. Athletes in ketosis can perform well at a steady endurance pace and can do so for many hours. All the while consuming far fewer calories than carbohydrate-dependent competitors. As a result, ketosis is a good solution for athletes who struggle with gastric distress. During exercise lasting 9-24+ hours, changes in blood volume, heat stress, and hydration status can slow or halt gut motility. This is a problem when you are consuming large amounts of carbohydrates. The fluid and food stay in the gut for too long to create gas, bloating, and nausea. GI problems are the leading cause of DNFs in ultramarathon events. The prevention of gastric distress makes dietary ketosis a solution for ultra-distance athletes. 

Problems with Muscle Wasting

The third problem with excessive carbohydrates is high fasting glucose levels. This leads to decreased muscle mass. The fancy term for this process called sarcopenia. Chronic endurance exercise is not sufficient to maintain muscle mass or function if you consume a high carbohydrate diet. A ketogenic diet is a protein and muscle sparing. No one wants to be a scrawny and weak, especially as we age.

Problems with Bonking

Last, but not least, a ketogenic diet for endurance athletes prevents bonking. Even very lean athletes have virtually an unlimited reserve of fat calories. We can only store 1600-2000 calories of carbohydrates. We store carbohydrates in the form of glycogen. If an athlete train becomes dependent on glycogen and unable to use ketones for fuel, the athlete will bonk. You have seen what happens when someone bonks…it isn’t pretty. Using fat as your primary source of fuel makes an athlete “bonk-proof”.

Sian Welch & Wendy Ingrham demonstrates what bonking looks like.

Performance Advantages of a Ketogenic Diet

We discussed earlier why we want to burn ketones as the primary source of fuel. Having 40,000+ calories of fuel onboard during an endurance event is pretty handy. Yet there are still critiques of the ketogenic diet that say it is all well and good that you can go for miles and miles, but can you go fast? Some athletes are concerned that they are not going to be able to do high-intensity work without consuming large qualities of carbohydrates. The recent study Rethinking the role of fat oxidation: substrate utilization during high-intensity interval training in well-trained and recreationally trained runners study should put their fears to rest. The study highlights the performance differences between high-performing and recreational athletes. The primary difference in performance is the rate of fat oxidation.

All athletes had similar rates of perceived exertion (RPE), blood lactate, and carbohydrate oxidation rates. The well-trained group had threefold higher rates of fat oxidation at high intensity. The body’s ability to make and use ketones is a decided advantage for the health and performance of any athlete. Athletic performance improves when the body uses fat as its primary source of fuel.

Adapting to a keto diet

I hope by this point you are at least curious and hopefully motivated to embark on training the body to make and use ketones. That’s great! Once adapted, you will likely never want to go back to the traditional high carb diet for endurance athletes. You may be asking yourself why wouldn’t anyone want to make the change. Here is the not so good news about a ketogenic diet. The process of changing your primary fuel source takes between 4-12 weeks. An athlete’s performance will suffer during this period. You will have a couple of days feeling like you have been hit by a semi-truck.  The key in adapting is to have patience, train in your MAF Heart Rate zone, and not skimp on the electrolytes.

Why doesn’t everyone recommend keto?

Concerns about high-intensity exercise

Many coaches and sports scientists were taught carbohydrates are required for performance. They may have bought into the idea that a ketogenic diet is great for low-intensity events but carbs are needed for high-intensity exercise. But is that true? The confusion is that when we hit our lactate threshold many scientists and coaches think we top burning fat. The confusion is in the Indirect Calorimetry Substrate Estimates. The problem isn’t that we stop oxidizing fat at high intensities, the problem is the testing equipment doesn’t know how to read the fat once we hit the threshold. Higher lactic acid-induced production of CO2 [through HCO3- buffering]. This has a large influence on the calculation of carbohydrate and fat oxidation. It creates an overestimation of the carb-burning. It also creates an underestimation of the fat burning. On the test, the estimation of fat use with these equations goes so low in fact that it often becomes zero, and then negative. Of course, you can’t have a negative for fat oxidation. Scientists typically misrepresent their data to say no fat is being burned. Rest assured, if you are keto-adapted, you can still oxidize fat at high intensities.

Concerns about Compliance

Once you spend a couple of months during the offseason to adapting, your body learns how to burn fat as fuel. It is pretty easy to maintain a high level of keto-adaptation once you have made the change. Once adapted, you can add some carbohydrates back in during training and during the training season. The key is to keep glycogen stores empty. This is possible by doing fasted workouts, warming-up fasted, and reverting to a ketogenic diet after workouts. This will ensure that your body will continue to produce ketones. During this period, your performance will continue to improve. Your health and quality of life with increase and your power outputs will continue to rise. Ketones are a clean-burning fuel you will generate less reactive oxygen species. Your recovery will be better.

Is it worth the effort?

I believe the performance gains alone are worth the effort. There are other reasons that you might consider going keto. Studies show that a ketogenic diet decreases triglycerides,  managing Type II diabetes, lower fasting blood sugar, lower fasting insulin, assist in cancer treatment, and improved cognitive function. These are the long term benefits of going keto. The nice side effects of better performance is worth the adaptation period.

Dietary ketosis does not require complete abstinence from carbohydrates. It is a matter of figuring out your personal limits. Learning how to train to deplete your glycogen stores will help ensure that you are never “kicked out of ketosis”. The way an athlete trains ensures their nutrition program is not sidelined by a slice of birthday cake, a beer at the ballgame, or a banana in an aid station. Learning how your body responds is the way to maintain the health and performance benefits of keto-adaptation

Need Help Adapting?

Further Reading…

Electrolytes, What do they do?

The Differences Between Being Fit and Being Healthy

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Coach Stephanie

Hi, My name is Coach Stephanie Holbrook. I learned how to regain my health and turn back the clock. I now help endurance athletes show you everything you need to maximize health, performance and a younger feeling body.

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