• David Martin

Is a Keto Diet Great for Endurance Performance?

Why are so many endurance athletes interested in the ketogenic diet? What is it about the diet that draws so much attention? Maybe it’s the claim to target and destroy fat helping you reveal that 6 pack had in high school, or it may be the article you read on it’s therapeutic uses for cancer treatments and epilepsy. Maybe you believe that it’s going to help you with your endurance racing how much weight you can lift in the gym. So…what’s the truth? Will this diet help me perform better in my triathlons? What is ketosis and what is a keto diet?

A keto diet is a very low carbohydrate diet that forces your body to produce what is called “ketones.” These ketones are derived from stored triglycerides, or fat, and your body uses them as an energy substrate. These ketones help you create ATP by entering something called the Krebs cycle in your mitochondria. ATP is the “currency” your body uses to help power many cell’s functions in the body including muscle contractions.

Let’s look at what a ketogenic diet entails…

1. You must eat a very low amount of carbohydrates. Many of the studies conducted found that 20 grams of carbohydrates or less a day is what is needed to put you into ketosis. That’s about a quarter of a banana a day. Some protocols allow up to a maximum of 40-50 grams of carbohydrates a day.

2. You must eat an adequate amount of protein but not too much! Why? If you eat more than 15-20% of your daily intake based of your resting energy expenditure of protein, your body will turn the extra protein you don’t need into glucose through a process called gluconeogenesis. Hence, your body will produce glucose and you may not be in ketosis anymore.

3. A typical breakdown of 75%, 15-20%, and 5-10% of your total intake from fats, protein, and carbs respectively.

So we know that this diet helps with fat loss. In a study looking at the effects of a 6 week non-energy restricted keto diet involving 46 people, the researchers observed an average weight loss of around 2.0kg with equal losses in fat and fat free mass. One marker that reflects muscle mass showed that muscle mass remained constant. These people were tested in a variety of ways including performance tests and physiological exams. Their bodies began to metabolize more fat at rest. In terms of performance, some parameters decreased such as VO2 peak, max power on a bike decreased, but handgrip strength increased slightly.

This study wasn’t target at athletes, and the researchers came to the conclusion that the impacts of physical fitness in a clinical sense wouldn’t effect activities of daily living. But, what if you’re a competitive athlete? What if you’re using this diet to help improve aspects of your racing?

We know that a major fuel source for the body is carbohydrates. We easily convert carbohydrates into a fuel source that helps our muscles and our body run, swim, bike, lift, etc for short and extended periods of time. But, we only have a limited amount of these carbohydrates in our liver, blood plasma, and muscles. So, what if we could teach our body’s to utilize more fat for fuel, thus saving these carbohydrates and possibly making us more efficient in longer endurance events. Here in lies the reason for some endurance athletes to try a ketogenic diet.

A study looking at elite race walkers, who range from world champions and Olympic medalists, implemented a ketogenic diet on 10 participants to see if their performance would improve. 29 data sets were collected from 21 male athletes (8 athletes completed the study on two separate occasions). The group was split into 3 diet protocols including high carb, alternating low carb and high carb days, and then a low carb group which was basically the keto group. The study took place over a 3 week training camp and began with a couple testing protocols including a 10k race, a treadmill test in the lab, and a long walk to look at running economy and fat/carb usage at different distances. After 3 weeks on their respective diets, the participants were re-tested to analyze if the diets affected their performances.

The results showed…

1. VO2 peak improved in all groups. During this treadmill test, the keto group did report a higher perceived effort to complete the test than when first completed while the other two groups reported lower perceived exertion the second time around.

2. The pre and post 10k race improved significantly for the high carb group and the alternating day group. The low carb group did not improve their times during the 10 k race.

3. During the 25 k long walk, there was an increased heart rate for the low carb group where as the high carb and mixed carb group produced lower heart rates. Perceived exertion tended to be higher for the low carb group than the other two groups. The low carb group certainly increased their percentage of fat oxidation by a significant amount.

So what do these results mean?

The researchers concluded that the low carb diet increased fat oxidation/metabolism but at the same time increased the oxygen demand on the body at all levels of intensity. The 10k race performance was a big topic of the discussion as the low carb group did not improve their performance compared to the other two groups. They concluded that the keto diet impaired exercise economy and inhibited training induced increases in aerobic capacity into the actual 10k race performance.

Why did this happen? Maybe the keto group wasn’t given enough time to acclimate to the diet? Even though they were technically in ketosis, they complained of side effects in the first week that probably took away from a good quality workout. People, and in particular athletes, who eat this way and report to perform well have been doing this for a longer period of time. Their bodies have probably adapted in a way that the 3 weeks didn’t allow.

I would argue that our bodies easily use carbohydrates for fuel, and as you train aerobically your body becomes much more efficient in utilizing triglycerides and fats at lower energy outputs. Recently I conducted a VO2 max test and I was surprised to see how much fat I utilized at 200 to 250 watts of power output on the bike with all the carbohydrates I eat. In a book written by Matt Fitzgerald, he interviews some of the best endurance athletes in the world. He also spends time with a professional cycling team as they complete a training camp. What he finds is that these world class athletes are eating a little bit of everything. They don’t leave anything out of their diet but eat a wide variety of very nutritious, healthy foods including carbs, fats, and proteins,

If you’re interested in a keto diet I would consult your doctor, research material written around the diet, and ask yourself why you’re doing it. Many more research articles are being released that show the opposite of what I wrote about and more studies are being conducted as I write this post.

Pay attention to your body, listen to how it feels, and in the end make sure you fuel yourself adequately to help you perform at your best.

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