Unlike keto, fasting is not a diet — it’s a method. Rather than giving you a list of foods to eat (or not eat), intermittent fasting alters how you eat. Specifically, it determines when you eat, veering away from the three-meals-a-day routine you’ve been taught since childhood. Keto fasting can be part of this.
Learning to make intermittent fasting work within your keto diet can help accelerate weight loss, enhance mental clarity, and improve your overall health.
If you’re new to fasting or a ketogenic diet, this is a great guide for beginners. Below, you’ll learn the basics of fasting while on the keto diet, the different approaches you can take, and the health benefits associated with fasting.
When people talk about fasting on the ketogenic diet, they’re usually referring to intermittent fasting. Intermittent fasting involves eating within a certain timeframe (called an eating window) and fasting for the remaining hours of the day (your fasting window).
There are different versions of intermittent fasting you can try, including:
If you’re just starting intermittent fasting, a gateway method is to simply skip a meal. Many people prefer skipping breakfast and choosing lunch as their first meal of the day. However, if you find that you’re not hungry at lunch or dinner, you could skip those instead.
Eating Within a Set Hour Window
Once skipping a meal seems manageable, you might try eating within a certain period of time each day. Many people refer to this method in fractions of 24, such as 16/8, 18/6, or 20/4, where the first number refers to the hours within your fasting window, and the second number representing the hours within your eating window.
The 16/8 method is one of the most widely used approaches in intermittent fasting. You can start your eating window whenever feels most comfortable. For instance, you could eat breakfast at 10 a.m. and dinner at 6 p.m., or start with lunch at noon and eat dinner at 8 at night.
Fat fasting is a specific kind of intermittent fasting where you only consume healthy fats during your feeding window. You can eat high-quality meat, nuts, seeds, coconut oil, MCT oil, and avocado, abstaining from sugar and carbs.
Alternate-day fasting is a rigorous approach to intermittent fasting — so only try it once your body is accustomed to going long periods without food. On an alternate day fast, you will eat normally one day (Monday), then fast for a full 24 hours (Tuesday). Typically, you shouldn’t conduct more than two 24-hour fasts per week.
The keto diet and intermittent fasting compliment each other very well. Partaking in a short fast can help you get into ketosis initially. Meanwhile, the high-fat foods you eat on keto will keep you fuller, longer — preventing hunger pangs that may accompany a fast.
Remember, it’s important to eat high-quality foods during your eating window. (It’s no excuse to consume carbs or sugar.)
Fuel up on high-quality protein, healthy fats, and leafy green vegetables. On your fasting days, you’ll eliminate your calorie intake entirely, sticking to water, black coffee, or unsweetened tea.
Tips for Keto Fasting
When fasting on a ketogenic diet, your goal should be to maintain ketosis, even during your feeding window. To ensure you stick to your keto meal plan, keep your energy levels in check, and follow healthy practices. Try these tips:
- Count your macros: During your feeding window, count your macros to ensure you’re eating enough high-quality fats and protein.
- Drink tons of water: You’ll be losing water at a rapid rate when you’re getting into ketosis. Make up for any water loss by drinking at least half of your body weight in ounces. That means: a 140-pound person will want to aim for at least 70 ounces of water daily.
- Supplement electrolytes: You also excrete electrolytes when you’re switching into ketosis. Make sure to take an electrolyte supplement, along with your increased water consumption.
- Test your ketone levels: Regularly test your ketone levels to ensure you stay in ketosis, whether you’re partaking in a fast or not.
- Catch a few zzz’s: Intermittent fasting is strenuous on your body. Ensure you’re getting enough sleep, controlling your stress levels, and practicing healthy habits.
- Make sure you eat enough: While it’s typically not recommended to count calories on keto, intermittent fasting is the one time to reconsider that strategy. Track your calories to prevent under-eating — a common side effect of fasting.
- Start slowly: If you’ve never tried intermittent fasting, don’t jump right into a 24-hour fast. Start by skipping meals, then move to the 16/8 method, and finally see how your body feels on a full day fast.
As you learned above, intermittent fasting and keto go hand-in-hand. Here are several benefits keto dieters experience from combining the two:
You Might Enter Ketosis Faster
Ketosis is a metabolic state that happens when your glycogen (stored glucose) reserves are depleted[*]. When you fast, your glycogen stores will be used up at a faster rate, thereby transitioning you into a fat-burning state. Therefore, you can enter ketosis faster.
It Can Help You Lose Weight
When you combine intermittent fasting with the keto diet, you might experience accelerated fat loss. In a fasted state, two things happen to your body that allows you to burn fat without reducing muscle mass[*]:
- You’ll (most likely) take in fewer calories: Intermittent fasting naturally reduces your calorie intake throughout the day. Eating within a set window eliminates late night snacking and overeating. Although you should take special care to ensure you’re not causing severe calorie restriction, chances are high you’ll take in fewer calories overall.
- You’ll likely be less hungry: This may come as a surprise, but you’ll likely feel less hungry when combining keto with intermittent fasting. A diet that reduces your carb intake while fueling you with healthy fats increases satiety levels and causes appetite suppression, thereby reducing cravings and hunger pains[*]
It Can Provide Mental Clarity
There are plenty of studies showing how a keto diet can improve brain health. Burning ketones (or fat stores) as your primary fuel source has been shown to reduce brain fog and improve alertness by keeping blood sugar levels stable[*]. A high-fat diet has also been shown to protect your brain from degenerative diseases such as Alzheimer’s[*].
Since intermittent fasting allows you to enter a ketogenic state faster, it may contribute similar benefits to a ketogenic diet. Research also shows that fasted mice experience improvements in their brain structure and function[*].
It Might Decrease Your Risk of Numerous Diseases
The combination of intermittent fasting and keto has been shown to decrease your risk of developing a number of diseases[*]. Intermittent fasting has been shown to reduce cholesterol levels, inflammation, and blood lipid levels, which are all biomarkers of heart disease[*][*].
Also, like the keto diet, fasting helps lower blood glucose and insulin levels, which can help decrease your risk of developing insulin resistance and type 2 diabetes[*].
There is a significant amount of overlap between intermittent fasting and the ketogenic diet. Both diets help you transition to a fat burning state, thereby supporting health and weight loss goals.
The two have similar health benefits, including balanced blood sugar levels, improved insulin levels, and a decreased risk of heart disease.
Fasting on keto can be a bit tricky: You’ll need to monitor your ketone levels regularly, track your macros, and potentially track your calories to ensure you’re eating enough. During your eating window, you’ll want to follow your keto diet plan to ensure you’re fueling up with high-quality foods.
If you’re interested in learning more about keto fasting, be sure to check out this beginner’s guide to intermittent fasting.