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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.

A guide to Exercise and the Keto Diet

Before we talk about exercise and the ketogenic diet, it is important that we address two common misconceptions regarding diet, exercise, and weight loss.

Misconception # 1:  Less calories in than calories out causes weight loss. Therefore, more exercise and less calories eaten equals even more weight loss.

Reality: Less calories and more exercise equals hunger, fatigue, stress, and ineffective weight loss.

No matter which way you look at it, your diet is the weight loss ‘game-changer’. What you eat is more important to weight loss than exercise.

Therefore, focusing on what you eat versus how much you eat is a much more successful and safe approach to weight loss.

This is where the ketogenic diet is such a useful tool to those wanting to lose weight.

Misconception # 2: You need carbohydrates to exercise  at optimal levels. Thus, low-carb diets decrease exercise performance.

Reality: Carbs are stored in the form of glycogen and are only used as a fuel source in quick bursts of high intensity exercise and can only sustain an individual for a few minutes of these types of exercises.

Fats are the main source of fuel for all aerobic exercise (i.e. long jogs or cycles) and are used as fuel once glycogen stores are depleted in anaerobic exercise (i.e. sprints or heavy lifting).

Once you understand the importance of diet over exercise, andexplained why you don’t necessarily need carbs for optimal exercise performance, you may be asking: should I even exercise on the ketogenic diet?

Although diet is arguably the most important variable to weight loss, exercise is also a key component to optimal health benefits.

Here are a few of the many benefits of incorporating regular exercise into your ketogenic lifestyle:

  • Improve bone mineral density (bone-loading)
  • Improve immunity
  • Increase cognition
  • Regulate mood
  • Reduce the effects of aging
  • Increase insulin sensitivity in diabetics
  • Prevent injury
  • Improve overall locomotion and flexibility
  • Burn 2-3x more fat doing endurance or ultra-endurance exercise (20-30+ minutes)
  • Prevent fatigue during long periods of aerobic exercise
  • Maintain blood glucose during exercise in obese individuals
  • Increased exercise performance overall

    What Should I Expect with Exercising on Keto Diet?

As your body is becoming keto-adapted (switching from using carbohydrates as a main fuel source to fats) in the first 2-3 weeks of starting the ketogenic diet, your exercise performance may be negatively affected. You may feel tired, fatigue, or even dizzy during exercise, especially anaerobic exercise (like heavy lifting or sprints) and you most likely won’t be able to perform at the same level as you did before.

It is important to note that these effects are short-term and performance will only suffer until you are keto-adapted. This is natural and due to your body’s natural transition from carbs to fats for fuel resulting in keto flu symptoms.

You will be able to presume regular aerobic exercise safely and efficiently after your body makes its’ transition to using fats as its’ main source of fuel, so have patience and trust your bodies normal process. How should you go about your exercise routine?

Exercising in the first few weeks on a keto diet

Before adaptation: Before being keto-adapted, in the first 2-3 weeks of adopting the ketogenic diet, you should stick to low-intensity, aerobic exercise for a majority of the time so as to prevent sugar cravings and muscle catabolism during exercise (i.e. yoga, Pilates, or long walks/ jogs).

You should also increase electrolyte and fluid intake (i.e. drink a large glass of water with a pinch of salt before working out). You should avoid doing high-intensity, anaerobic exercises until you’re are keto-adapted because it can be counterproductive to adaptation and you will have decreased performance during this time period. We keep saying anaerobic exercise versus aerobic exercise and you may be unfamiliar with these terms. As a general rule of thumb: if you can breathe easily through your nose without panting during the exercise, it is an aerobic exercise. These include things like 20-30 minute + jogs and cycles. If you cannot breathe easily through your nose during an exercise, these exercises are considered anaerobic. Examples of anaerobic exercises include: heavy weight lifting, sprints, and explosive sports like soccer, lacrosse, hockey, etc. However, exercise in general will help you get into ketosis faster, so that is not a deterrent from embarking on exercise during this time frame. Instead, you should focus more on endurance and mobility.

Bottom line: Before keto-adaptation you will experience an initial drop in performance. During this time period you should increase electrolytes (sodium) and fluids and stick to low intensity, aerobic exercise.

After keto-adaptation: After you are adapted to using ketones and fat for fuel, your energy levels will improve along with your training. Your aerobic exercise performance will increase, you will burn more fat and feel less fatigued during these exercises. Studies have suggested that a keto diet will increase endurance or ultra-endurance athlete performance, lead to greater fat loss in these individuals, and maintain their muscle mass.

The benefits of keto diet  for athletes

Becoming keto-adapted using a ketogenic diet can also specifically help aging athletes who struggle with impaired recovery, increased body weight, and have difficulty maintaining desired body composition. In addition to these aerobic performance effects, anaerobic exercise performance should proceed almost back to normal levels, if not normal.

It is expected that you will be able to perform at 90% of maximum equally as good anaerobically. Your muscle glycogen stores that fuel these types of exercises will be replenished despite lack of carbs and with the increased ability to use fats for fuel, you won’t tap into glycogen stores as often.

An everyday, moderately active individual will experience less fatigue during exercise and greater performance on a normal ketogenic diet. Those that do more intense, anaerobic exercise often may want to consider adapting the ketogenic diet to optimize anaerobic performance.

Here are two ways to do so:

Targeted ketogenic diet (TKD): Eat 25-50 grams or less of fast-acting carbs (i.e. whole fruit) within 30 minutes of workout and/or 30 minutes after workout. This will ensure that your body has the proper amount of glycogen to perform during training and recover after. This will not take you out of ketosis, as your body will use up this glycogen during training and after for recovery.

Cyclical Ketogenic Diet (CKD): Eat strict keto for 5-6 days to get the benefits of ketosis, then eat a higher carb diet 1-2 day a week to replenish glycogen levels and help improve high intensity performance. This can be especially helpful for athletes who train throughout the week and can up their bard intake to perform well in games/ matches on weekends.

The standard ketogenic diet can lead to increased fat loss for the normal individuals and increase exercise performance of ultra-endurance, endurance, and aging athletes.

It is possible to receive all the health benefits of the keto diet and be able to participate in regular exercise or preform at a high level as an athlete.

After being keto-adapted, aerobic exercise performance may increase, as your body can use fats for fuel more efficiently and you experience less fatigue.

– Dr Jerry Hizon, MD