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Fasting on Keto: Pros and Cons Explained

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Melissa Mitri post Reviewer Melissa Mitri post Reviewer
Verified by Melissa Mitri
MS, Registered Dietitian, Former President of CT Academy of Nutrition & Dietetics

Table of Contents

The ketogenic diet and intermittent fasting are different weight loss strategies that more or less rely on the same mechanism. 

Both methods have been recognized as effective approaches for losing weight on their own, but what happens when you combine these two? Will fasting on keto bring faster weight loss? Let’s find out. 

Basics of Keto

If you’re a regular reader, you probably know the basics of the ketogenic diet, but let us quickly bring you up to speed.

The keto diet is a diet plan focused on eating low-carb, moderate-protein, high-fat meals. 

If you are practicing the keto diet, you are expected to obtain 70-80% of your daily calorie intake from fats and 10-20% from protein. Furthermore, you should limit your carb intake to 5-10% of your daily calorie requirement [1]

The state of ketosis mainly drives the weight loss your body goes through when you’re on the keto diet. Ketosis occurs when your body uses up all the available carbohydrates and then starts burning fat reserves to generate energy [2]

Eating extremely low amounts of carbohydrates, similar to a keto diet plan regularly will deplete your body’s carbohydrate stores and eventually trigger ketosis. 

The ketogenic diet has been proven to bring about several benefits such as [3]:

  • Helping with weight loss
  • Controlling the appetite
  • Reducing visceral fat, the type of fat around your organs
  • Improving the lipid profile, such as cholesterol and triglyceride levels
  • Improving blood sugar levels

Basics of Intermittent Fasting

Intermittent fasting (IF), as the name implies, involves fasting regularly. This eating plan focuses on restricting your meal timing rather than your meal composition. You can choose the method that suits you the best from many fasting schedules, such as 16:8, 5:2, or 24-hour fasting once a week.  

The benefits of intermittent fasting are also rooted in ketosis, which kicks in after about 12 hours of fasting [4]. If your fast lasts for 24-48 hours, you can induce autophagy, the process of breaking down and reusing old and damaged cell parts [5]

These are the two processes thought to be behind the health benefits that intermittent fasting produces. These benefits include [6]:

  • Reducing body weight
  • Lowering blood pressure
  • Reducing blood glucose
  • Controlling inflammation
  • Improving brain health

Fasting on Keto: The Pros of Combining the Two

As you can see, intermittent fasting and the keto diet bring about weight loss by putting your body in ketosis. 

So, what will happen if you combine the keto diet with intermittent fasting? 

The general idea is that keto and fasting approaches will complement each other and help you achieve your weight goals faster.

Here are some pros of fasting on keto:

Intermittent fasting on a keto diet can get you over a weight loss plateau

If you’re already on keto but your weight loss has stalled, trying intermittent fasting while following the keto diet might be a good idea. Limiting your window of time to eat can help reduce calorie intake, which can tip the scale in the right direction again.

We highly recommend consulting your doctor or a registered dietitian before starting.

Intermittent fasting will help you achieve ketosis faster

If you just started keto or are returning to keto after a cheat day and want to get into ketosis quickly, you can try intermittent fasting. Intermittent fasting will deplete your carb reserves within 12 hours, while it will take 2-4 days to enter ketosis if you follow the keto diet alone [2]

It will help you control your calorie intake

Even with following the ketogenic diet, you must maintain a constant calorie deficit to lose weight. 

However, it’s easier to go over your daily caloric requirement when you eat calorie-dense, high-fat meals—especially if you snack a lot. Intermittent fasting will restrict your eating time, thus naturally controlling your calorie intake. 

IF has also been reported to reduce appetite, which helps to control food consumption [7].

Intermittent fasting will boost your metabolism

Intermittent fasting is known to speed up fat metabolism, thus promoting weight loss [8]. The combined effect of intermittent fasting plus keto will produce faster and more significant weight loss.  

Cons of Fasting on Keto

Although fasting on a keto diet can speed up weight loss, there’s also a flip side. This article will not be complete without discussing the potential drawbacks of fasting on the keto diet. So, here are some limitations and risks of combining these two weight loss methods:

It can be too restrictive for some people

Fasting on keto is not for the faint of heart. The keto diet significantly reduces carb intake, and intermittent fasting lowers food intake to a limited number of hours. It can be too much of a restraint for some to incorporate intermittent fasting into an already restrictive keto diet plan. 

Moral of the story – you’ll need to have a lot of willpower to practice both of these diet plans at the same time. 

Going low carb and doing intermittent fasting can cause low blood sugar levels

Going without food for extended periods while on a low-carb diet can cause dips in blood sugar levels. This can be dangerous for those who have issues related to glucose metabolism. 

You might also like: Ideal Blood Sugar Levels for Weight Loss

You can end up with severe nutritional deficiencies

Since both of these methods restrict food intake in one way or another, you risk developing critical nutritional deficiencies if you’re not cognizant of your dietary choices.  

It can result in unwanted conditions like ketoacidosis in some people

Blending a strictly low-carb diet with prolonged fasting has been reported to result in a condition called ‘starvation ketoacidosis’ in a person with controlled type 2 diabetes [9]. Ketoacidosis increases your blood acidity, which can be life-threatening.  

How to Do Fasting on Keto

Now that you have enough facts to decide whether fasting on the keto diet is for you let’s see how you can safely and effectively incorporate intermittent fasting on a keto diet.

Find the best fasting duration for you

Start with a shorter duration, then gradually increase the number of hours you fast until you find the most comfortable method.  You can start with the most popular regimen, 16/8 (or even gentler 14/10 regimen).

Plan your meals ahead

The ketogenic diet limits your carbs, thus cutting down your fruit and vegetable intake. If not careful, this can result in severe malnutrition concerning essential vitamins and other nutrients such as fiber. 

Planning your meals allows you to eat various nutritious fruits and veggies without exceeding your carb limit.  

Try modified keto if the original plan feels too restrictive for you.

You can try a modified keto diet if you find the original keto diet too difficult. 

Should You Combine Keto and Intermittent Fasting?

So, is it a good idea to combine intermittent fasting with keto? 

There can be benefits to practicing both of these strategies together. It can produce faster weight loss results and benefit those struggling to lose weight or have hit a weight loss plateau. 

However, as we discussed, merging these two methods can have its downsides, too, especially if you have an underlying health concern. 

On that note, it’s best to consult a doctor before integrating fasting into your keto diet if you have health conditions such as diabetes, heart disease, or kidney disease. 

Bottom Line

  • The ketogenic diet and intermittent fasting can result in effective weight loss, both independently and when combined. 
  • While fasting on keto can bring several benefits, there are potential drawbacks.
  • The best strategy is to start slow and see how the combination of the two methods works for you. 
  • A little planning ahead can improve your chances of succeeding. 
  • If you’re pregnant, breastfeeding, or have an underlying health condition such as diabetes, consult your doctor before trying out a new diet strategy.  
Disclaimer This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!

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