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Carbs, Exercise and the Keto Diet: what you need to know

A lot of people who are on a ketogenic diet wonder what the best types of food are when exercising. They are told not to eat carbs, but also that carbs can help with exercise. Keto and exercise is a confusing topic and one that I will try to demystify.

First of all, you body has different types of fuel. The most common type of fuel most people burn when exercising is carbs. This is because carbs provide a faster ‘burn’ and are great for explosive exercise.

What does it mean to carb-load before exercise?

You might have heard of the term ‘carb loading’ which is what a lot of athletes will do the day or evening before an event. It can provide the energy boost needed in that short period for better performance.

But here is the challenge of carbs: most people are not elite athletes. We exercise moderately, usually one to three days a week. So the majority of the time, our carbs are not being used for explosive energy.

Why is exercise harder on a keto diet?

When a person first takes on a ketogenic approach to eating, they can find it is hard to exercise. This is especially true in the first few weeks of a keto diet (link) because they feel a lack of energy.

Rest assured when you first start exercising on a keto diet, this is normal. Your body is becoming fat-adapted, meaning it is switching from burning carbs to burning fats.

Are you exercising with the wrong fuel?

To further fuel analogy: you can think of carbs and fat like gas and diesel. Both can power vehicle, but are used in different ways. Gas is more like carbs, in that it burns quickly. Diesel is a slower burn, more like fats in your body.

For years, experts have derided fats in our diets, but we are now seeing that humans are more like diesel vehicles, which perform well with a slow burn.

When you first start a keto diet, the exercise you do will trigger your body to burn carbs. But after a few weeks on a ketogenic diet when there is little ‘carb fuel’ left, it will start to burn fat and ketones as fuel.

Here are some symptoms you feel when first exercising on a keto diet:

  • Lack of stamina compared to past performance
  • Lack of explosive power
  • Lack of muscle strength
  • Muscle cramps (usually due to low sodium or dehydration)
  • Need for more water
  • Need for more sleep


How often should you exercise per week on a keto diet?

As a rule, if you exercise less than 2 hours a week, then ketones (fat) are good fuel source. They will help you to lose weight, and your stamina and strength will increase if you persist.

If you exercise an hour or more per day, or you participate in activities like crossfit or cycling, then you may benefit from some additional carbs to give you additional fuel.

With around 80% of people above their ideal weight, the keto diet combined with moderate exercise can be an excellent combination to help you. If will give you slow burn and assist with long term weight loss. If you go a little easier on yourself during your first few of exercise weeks on the keto diet, you will soon see an improvement.

Jerry Hizon, MD is a ketogenic doctor based in Murietta, California. He assists people wanting to lose weight and improve their health through ketogenic diets. His keto coaching programs can help you to track your progress and improve your success. Visit his website today to learn more, or signup online for a keto coaching session via nudge coaching.