Benefits of Fasting on the Ketogenic Diet

If you’re like most people, the idea of skipping a meal--or even going an entire day without eating--runs counter to everything you’ve learned about breakfast being the most important meal of the day.

While this logic seems sensible on a high-carb, low-fat diet with its accompanying dips and peaks in blood sugar, the keto diet is an entirely different animal. When your body has adapted to using ketones and fat for energy, you’ll no longer need to continuously refuel to maintain energy levels.

While fasting isn’t a requirement of the ketogenic diet, many people choose to use some form of intermittent fasting with some regularity because of the potential benefits.

Fasting with Keto

The keto diet is, all by itself, a terrific tool for appetite control. The balance of low carb, high fat, and moderate protein has a naturally sating effect that helps manage portions and calorie intake effectively--without hunger.

Just like keto, intermittent fasting shouldn’t be an exercise in willpower or going hungry. Whether you decide to fast during specific hours every day, or choose to fast for longer periods of time at regular intervals, fasting should be natural and intuitive--not an exercise in starvation. During the days and hours you do consume food, you should pay special attention to meeting your macronutrient requirements to ensure proper nutrition and avoid muscle loss.

Benefits of Intermittent Fasting

Many studies have documented health benefits of intermittent fasting. While these benefits are not specific to fasting during a ketogenic diet, the ease with which fasting can be done during keto is all the more reason to take advantage of these potential benefits:

Decreased Inflammation and Insulin Sensitivity

Several studies show that intermittent fasting can improve insulin resistance, increase sensitivity to insulin, and reduce inflammation.


In the most basic sense, autophagy is the body’s ability to repair or eliminate damaged cells (including cells that may become cancerous). Autophagy both slows the aging process and keeps the body in good working order--and is most effective during a fasting state.

Mental Clarity

When the body transitions to using fat, rather than sugar, as an energy source, the need for constant refueling disappears. The body becomes adept at accessing fat stores for energy, meaning that dips in “brainpower” disappear, replaced by steady mental focus and clarity. During fasting periods, this mental clarity can be even more focused.

Enhanced Fat Burning

While you are fasting, your body will access stored fat for energy (since glycogen is no longer available, and consumed fat is no longer being ingested). As long as you do not extend your fast for prolonged periods (longer than 5 days), there’s no need to worry about muscle loss, since fasting has a positive impact on muscle recovery and preservation.

Kickstart Ketosis

Beginning your keto diet with a planned fast can be a helpful way to burn through your stored glycogen and trigger the production of ketones in the liver. Many people begin their keto diet with a 24-48 hour fast, drinking water and unsweetened coffee and tea only.

During an initial fast, the body will burn through glycogen stores first, then begin producing ketones to access stores of fat. This isn’t the right method for everyone when it comes to starting a keto diet. If you feel distressed or faint, listen to your body’s signals and eat small amounts of fat and protein. In addition to fasting, many people choose to take BHB (Beta Hydroxybutyrate) supplements, to maintain energy levels and kickstart ketone production before the liver begins producing ketones on its own.

Power Through Plateaus

There are few things more frustrating than a plateau in your progress--especially when it comes to weight loss. Intermittent fasting is a great tool to regularly “reboot” your keto diet and ensure that ketone levels stay high. It can be easy to let additional carbs creep into your diet through snacking, additional portions, or hidden carbohydrates--meaning decreased ketone production. Skipping meals when it feels right, or fasting for 24-48 hours can help the body reboot and rely on fat stores and ingested fat instead of glycogen.

If your goals include weight loss, and you’re struggling with a plateau, it may be helpful to break down the day into a fasting window and a feeding window. By limiting the window during which this intake occurs, it’s possible to significantly reduce the number of calories you eat during a day, without feeling deprived during any given meal.

How to Fast

There are many options for fasting on a keto diet. It can be helpful to start with the most conservative method (skipping meals or condensed window) and work up to extended fasting. Remember, the goal isn’t to starve your body or white-knuckle a fast. Approach fasting intuitively, and do what feels right!

Condensed Window

Eating only during a specific window of time each day is known as “condensed window” fasting. Many people eat only during evening hours (e.g., from 4pm to 10pm), or skip breakfast each day and eat from 12pm to 6pm. You may see these hours broken down as 20/4 (20 hours fasting, four hours eating). During the feeding window, eat as regularly as you wish, until you’re satisfied, keeping macros balanced and making sure to hit your protein goals. During your fasting window, you’ll drink only water and unsweetened tea and coffee.

Skipped Meals

Many people find that a simple way to shorten their feeding window is to simply skip breakfast or dinner if it feels natural. Don’t force anything, and don’t continue if you get too hungry. You can build up to skipping meals and increasing your fasting window by gradually pushing back meals each day. Listen to your body, and eat only when motivated by hunger!

Extended Fasting

Most keto beginners don’t use extended fasting at first (unless the extended fast is used to kickstart ketosis) since the body needs time to adapt to using fat for fuel. However, once you are adapted to keto, extended periods of intermittent can yield many of the health benefits detailed above! While the human body can go for extremely long periods of time without food, it’s best to keep your fast to 24-48 hours, and no longer than five days. Fasting for very extended periods of time can have negative consequences when it comes to nutrient loss and muscle deterioration.

Exercising While Fasting

Once you have become keto adapted and your body is smoothly using ketones to convert fat into energy, it’s not only possible but beneficial to exercise during a fast. As long as you maintain proper macro levels during your feeding periods and stay hydrated, you’re likely to notice the following benefits of exercise while fasting:
  • Improved training performance: Several studies show long-term improvements in performance stemming from exercise during a fast
  • Improved fat loss: Without stores of glycogen or ingested fat and protein, it’s possible to access and burn stored fat easily while in a fasting state
  • Muscle gains: While surprising, it’s true that muscle mass can be gained during fasting! As long as you are maintaining proper macros during feeding, and keeping key nutrient levels high, it’s more than possible to maintain and gain muscle during fasting.

Healthy Fasting

Fasting should be natural and intuitive--and it may not be right for you! Individuals with diabetes, premenopausal women, and women who are pregnant should only fast under the supervision of a doctor.

During your feeding window, and the times before and after a fast, make a special effort to eat real food that is rich in nutrients, high in fat, and moderate in protein. Make the food you eat count!

Make sure to stay hydrated during a fast. Water is important for all your body’s functions, and while the body is physically able to go without water, it isn’t ideal by any means. Proper hydration will also help ensure proper ketone production in the liver while you fast.