Fat Fasting on Keto Diet: Is It Healthy? Does It Work? | KetoVale
fat fasting

Fat Fast – A Complete Guide for Beginners

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What’s the first thing that comes to mind when you think of a regular fast? Probably misery, right? You might imagine things like only being able to drink water for several days with no solid food.

Now picture this. You get to eat fat and not much else for several days at a time. If that sounds good to you, then read on.

The fat fast is often used by many ketogenic dieters to help them get into ketosis faster. It involves limiting your calories to up to 90% fat for several days.

You’ll also need to cut your calories in general, but because you’ll be eating fat, you won’t feel as hungry as you would during a normal water fast.

However, there are some drawbacks to fat fasting that you need to be aware of before starting. Check out more information below in our complete guide for fat fasting for beginners. 

What is Fat Fasting?

Fat fasting is a type of fast that involves eating approximately 80% to 90% of your calorie intake fat for several days. It was made popular by Dr. Atkins in an attempt to help his patients control type 2 diabetes.

You can think of it as an extreme version of the ketogenic diet, which involves getting approximately 75% of your calories from fat, 20% from protein, and 5% from carbs.

In addition to eating a very high-fat diet for several days, fat fasting encourages you to reduce your overall calorie intake to 1,000 to 1,200 per day.

Fat fasting was designed to help encourage your body to produce ketones as quickly as possible, which is the metabolic state in which your body burns the most fat. 

When you limit your calories as well as your carbohydrate intake, your body stops relying on glucose as fuel and instead switches its energy source to fat. It forces your body to burn fat because you stop feeding it other nutrients (like carbs) that it could potentially use as energy instead. 

You can achieve ketosis normally by following a regular ketogenic diet, but the fat fast is a quicker way to achieve the same results. And the sooner you enter ketosis, the sooner you’ll become a fat-burner instead of a glucose burner!

For this reason, the fat fast is popular among people who follow the ketogenic diet. It’s especially beneficial if you have been on the ketogenic diet for a while and have hit a plateau with your results. 

You can also use a fat fast to get back into ketosis if you have been kicked out, or to get over the symptoms of the keto flu quicker.

Are There Any Health Benefits of Fat Fasting? Is It Healthy?

The primary benefit associated with the fat fast is that it helps you lose weight quickly by having a calorie deficit and putting your body into a state of ketosis where you burn fat as fuel.

There are not many studies on fat fasting in particular, however, other benefits of eating a high-fat low-carb diet are already well established.

Several studies have proven that the ketogenic diet helps with the following:

  • Promotes weight loss
  • Reduces hunger and cravings
  • Enhances athletic performance 
  • Improves body composition
  • Reduces blood sugar levels
  • Possesses anti-tumor abilities
  • Serves as a treatment for epilepsy
  • Enhances brain power
  • Reduces the risk of neurodegenerative diseases
  • Reduces the impact of migraines
  • Reduces inflammation
  • Supports heart health

There are few, if any, studies done on the effects of the fat fast diet, but many have been done to show the health benefits of eating a high-fat diet in general. These benefits are multiplied when you pair them with low-carb eating.

For example, research shows that a high-fat diet may have the following benefits:

  • Reduces inflammation
  • Reduces the risk for cardiovascular disease
  • Improves depression symptoms
  • Improves brain function 
  • Enhances sports performance 

The fat fast diet floods your body with a steady supply of ketones. By switching your fuel source from glucose to fat, you’ll experience more energy, less mental fatigue, and better weight loss. Many people who follow a low-carb, high-fat diet are also able to reverse their type 2 diabetes.

This is because insulin is a fat-storing hormone. It transports glucose that isn’t being used to your adipose tissue where it’s stored as fat. On the other hand, ketones are not stored as fat. 

They are instantly used as energy or they are excreted via the urinary system. This means that there is no excess energy in your body that needs to be stored somewhere until they can be used. 

Eating a high-fat diet also keeps you full for longer periods of time so that you eat fewer calories throughout the day. A diet rich in omega 3 fatty acids helps reduce inflammation, which can help with a variety of symptoms that range from digestive upset to skin problems.

For a complete list of studies and proven benefits of a high-fat and ketogenic diet, see our list here.

Bottom line: Fat fasting restricts your calories and protein intake as well as other essential micronutrients, therefore, it is not recommended as a long-term plan. It’s better to follow a well-formulated ketogenic diet with enough protein, fiber, nutrients, and carbohydrates from low-carb veggies.

How To Do The Fat Fast

During the fat fast, you’ll need to restrict your calories to 1,000 to 1,200 per day. Your calories must contain 80% to 90% fat, which leaves only 10% or so for other calories.

If you are on the ketogenic diet, then you will want to continue to make sure that your remaining calories only contain about 5% carbs. This is to ensure that you stay in ketosis

By flooding your body with foods that contain almost all fat, you will quickly start producing ketones and enter ketosis.

You can stay on the fat fast for 2 to 3 days. We don’t recommend going over this time period if you’re just starting out. This is because severely limiting your calories for several days at a time may cause you to become malnourished and fatigued. Furthermore, not eating enough protein will risk losing your muscle mass.

It’s a good idea to start with a two day fast to see how you react to it before continuing on with longer periods. After fat fasting for two to three days, you should start producing enough ketones to successfully return to your normal ketogenic diet where you should continue to see results. We recommend waiting two weeks in between fasts before fasting again. 

You can start your fat fast by dropping your calories to 1,000 to 1,200 calories per day, broken up into several small meals to help you feel full.

What to Eat

Here is a list of some foods you can eat on the fat fast:

  • Avocados and avocado oil
  • Macadamia nuts
  • Olive oil
  • Coconut oil
  • Cheese
  • Cream cheese
  • Fat bombs
  • Whole eggs and egg yolks
  • Full fat coconut milk
  • Bacon and pork
  • MCT oil and powders
  • Beef and steak
  • Oily fish
  • Chia seeds
  • Flaxseeds
  • Homemade mayonnaise
  • Sour cream
  • Heavy cream
  • Nuts and nut butter
  • Pumpkin seeds
  • Almond flour
  • Coconut flour
  • Butter and ghee
  • Olives

You can pair your high fat foods with low-carb veggies to help get your fiber and antioxidant intake up. Focus on spinach, kale, broccoli, cabbage, and cauliflower. Add MCT oil and grass-fed butter to your coffee, and snack on fat bombs in between meals.

Avoid all foods that you would normally avoid on a ketogenic diet, such as beans, bread, processed food, most fruits (except for berries), potatoes, rice, grains, and milk. These foods are high in carbs and are not a good source of fat. 

For meal ideas and a list of high fat recipes that you can enjoy during your fat fast, see our recipe list here. All of our meals come with a nutritional breakdown so you can see how many fat calories you are getting in.

Potential Risks Associated With The Fat Fast

The fat fast diet isn’t for everyone, especially if you don’t already follow a ketogenic diet. First, it requires you to reduce your calorie consumption. Depending on how many calories you’re currently eating, this reduction in calories can make you feel lethargic and fatigued. 

You may want to spend a few days gradually reducing your calories until you hit two days worth of 1,000 to 1,2000 calories. Then return to your normal caloric intake following the ketogenic guidelines.

In addition to restricting your calories, the fat fast also requires you to eat 80% to 90% of your calories from fat. You’ll be missing out on a lot of micronutrients, protein, antioxidants, fiber, and antioxidants that you would normally get if you follow a balanced low-carb diet.

The lack of protein in addition to the lack of calories may cause you to lose muscle mass (1). This can be concerning for some people, especially athletes.

We only recommend that you try the fat fast if you are already on the ketogenic diet, but have hit  a plateau with your results. A fat fast can help rapidly increase your ketone production to help you lose weight and better control blood sugar levels. 

The fat fast can help you get over the keto flu quicker by propelling you into ketosis, but it can have the opposite effect if you’re new to keto by causing you to experience keto flu symptoms.

Here is a list of possible side effects associated with the fat fast:

  • Fatigue
  • Headaches or migraines
  • Digestive upset including constipation, diarrhea, cramps or bloating
  • Inability to focus or concentrate
  • Nausea or dizziness
  • Inability to exercise
  • Problems sleeping

If you’ve hit a plateau in your ketogenic diet and you don’t want to try the fat fast diet, then we recommend checking out intermittent fasting. It requires you to limit your calories several times per week to achieve similar weight loss results as the fat fast.

Both methods can help you overcome a weight loss plateau. The difference between the two is that intermittent fasting does not require you to limit your calories or eat a high fat intake.

This means that unless you’re already in ketosis, intermittent fasting won’t necessarily help you get there (unless you restrict the carbs you eat to fewer than 5% of your total calories). 

You can learn more about the health benefits of intermittent fasting and how to get started


The fat fast requires limiting your calorie intake to 1,000 to 1,2000 per day for two to three days. The fat fast also requires that you eat 80% to 90% of your calories from fat.

Many people on the ketogenic diet use it to overcome hitting a plateau with their weight loss results. It works by propelling your body to produce ketones, which helps put you into ketosis where you can burn fat as fuel instead of glucose.

We recommend only using the fat fast diet if you’re already on the ketogenic diet and are familiar with being fat adapted. Otherwise, a big change in your diet might cause unwanted symptoms, such as fatigue, problems concentrating, and digestive issues.

If you have hit a plateau in your ketogenic diet, then you can check out intermittent fasting, which requires you to limit your calorie intake similarly to fat fasting. The difference is that you don’t have to limit your calories to 80% to 90% fat only. Both diets can help you overcome a weight loss plateau and help you continue on with your ketogenic journey!

Up Next: The Truth About The Egg Diet and Egg Fast

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