Chances are that you or someone you know is on the keto diet or has at least tried it. Many people have seen positive results with this low-carb, high-fat diet approach including weight loss and improved energy. With so many people touting the benefits of this diet, it seems that very few are talking about the drawbacks, including how it affects exercise.

Keto is great for exercises involving lower intensity sessions such as long walks, Zumba, or light strength training. The struggle starts to happen with higher intensity training. This can include High-Intensity Interval Training (HIIT), CrossFit-style workouts, heavy weight training, or running at higher speeds. These are workouts that are popular and effective. So why is it so much harder to work out at higher intensities on the keto diet? It has a lot to do with physiology.

When someone has adapted to a keto diet, the metabolic “machinery” has shifted to burning mostly fat for fuel, and there is less flexibility to switch from burning fat to carbohydrate. In addition, with a very low intake of carbohydrate foods, there are fewer carbohydrates available to be used as fuel. During lower intensity workouts, the body can readily use fat for fuel because the energy demand is lower and it is easier for the body to use them to fuel the muscle cells. As the intensity goes up, there is a greater demand for energy. Carbohydrates are broken down for fuel more rapidly and thus are the preferred energy source during higher intensity training. In fact, the research indicates that as the intensity goes up, the ability to use fat for fuel goes down.

So, what is the solution for those who want to be on a keto diet and also continue their same exercise routine?  Here are some suggestions:

Don’t under-fuel

Many people on keto do not eat enough because of the satiating effect of fat. In addition, because a significant amount of foods are off limits (any foods high in carbohydrate), there are fewer food groups available to choose from, which may also limit intake. This is one reason the keto diet is so effective for weight loss. The keto diet is a moderate protein diet, but it is important to get enough to stimulate the body to maintain muscle mass.

Consider lower intensity training

Fat will be the predominant fuel source during low-intensity training on a keto diet, so take advantage! If you do high-intensity training every day of the week, that might leave you feeling depleted on a keto diet, so try switching it up and try to incorporate more lower intensity sessions.

Don’t forget the strength training

Strength training will be very important for anyone on the keto diet wanting to maintain muscle mass. Essentially, strength-training acts as a stimulus to our body to preserve muscle mass. This is particularly important for those following the keto diet, as research suggests this approach may stimulate muscle loss. Consider using a weight that is lighter to moderately heavy and doing 3-4 sets of 8-12 reps with plenty of rest in between, which should keep the intensity relatively low. Keep in mind there is a higher energy demand and intensity needed to lift very heavy weights and activities such as powerlifting will be a challenge on the keto diet. According to the research, gaining muscle mass can also be difficult on this diet because carbohydrates are important for stimulating muscle growth.

Change your expectations

If you do higher intensity exercise on a regular basis, you may need to change your expectations. This diet may have benefits, but don’t be disappointed when you don’t see any improvement in higher intensity activities. If you implement the keto diet correctly, it has the potential to be effective in decreasing body fat while maintaining muscle mass. This can be a hugely positive benefit of the diet. However, don’t expect to have large or even moderate increases in strength or muscle mass.

Support Your Training with Supplements

• Electrolyte shifts on keto can make exercising even more difficult. Consider an electrolyte supplement before the workout. Make sure it is low in sugar.  
• Exogenous ketones can act to spare the use of carbohydrate during exercise. This can improve aerobic or lower intensity exercise, but there may be benefits to using them for higher intensity exercise and they may enhance recovery.
• MCT oil can enhance endurance and may be a good choice for longer endurance activities
• Lower carb protein powders can be beneficial before or after exercise to stimulate muscle growth and maintenance.

• HMB or beta-hydroxy-betamethylbuterate may have a muscle sparing effect, which can be helpful on the keto diet.
• Creatine monohydrate can positively impact muscle strength, which is important on the keto diet.