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What is a Fat Fast and Should You Try It?

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  Published on July 19th, 2020
  Reading time: 3 minutes
  Last modified February 3rd, 2023
fat fast on keto

Fat fasting is a method of dieting used to accelerate weight loss. Many people use this method to breakthrough weight loss plateaus or to get back into ketosis after a cheat day. Let’s answer some important questions about this fasting method like what is a fat fast, is it safe, and is it effective?

What is a Fat Fast?

When you’re fasting you refrain from eating for a certain time period and you have fasted and feeding windows. Fat fasting isn’t technically a fast, rather, it raises your blood levels of ketone molecules and helps your body get into ketosis, which mimics the biological effects of fasting [1].

A fat fast is a low-calorie, high-fat diet that usually only lasts for 2-5 days. During a fat fast, you consume between 1000 to 1200 calories a day and around 80-90% of that should come from healthy fats, such as:

The portion of fat in your diet should be around 80-90% with an emphasis on oils, creams, and butter. High-protein foods like chicken, meat, and fish are normally consumed in moderate amounts on keto. These foods aren’t often included during a fat fast because they can push your protein intake too high. 

You might decide to add a small amount of meat to your fat fast for flavor but use it sparingly and focus on high-fat creams, oils, and butter. On a fat fast, you avoid foods that are high in protein and carbs and low in fat.

Should You Try a Fat Fast?

You might try a fat fast for numerous reasons. Some people try a fat fast to get into ketosis faster. The time it takes to get into ketosis varies considerably depending on several factors, but on a traditional ketogenic diet, you can expect to reach ketosis in 2-6 days. With fat fasting, you restrict both calories and your carbohydrate intake, which can get you into ketosis quickly or boost ketone levels if you’re already in ketosis [2].
You might try a fat fast if you’ve hit a weight loss plateau or if you’re struggling with hunger cravings.

Many keto dieters try a fat fast for a smoother recovery back into ketosis after a cheat day — where you eat high-carb foods that aren’t keto-friendly.

What are the Benefits of a Fat Fast?

A fat fast quickly depletes your body’s carbohydrate stores, so you burn more fat and shift your metabolism into ketosis. If you adhere to a fat fast protocol for 2-5 days, you might enter ketosis or boost ketones and primarily burn fat for fuel. The lack of dietary carbs, calorie deficit, and caloric restriction, and the boost in ketones can help with weight loss [3].

Since a fat fast is usually short-term, some of the weight loss might be water weight. When your body loses carb stores it also leads to water loss, which is stored alongside glycogen — the stored form of glucose. This is most likely if you’re not already keto-adapted or if you’re doing a fat fast following a cheat day [4] [5] [6].

 With a fat fast, you’re not overloading your body with lots of calories and straining your digestive system. You consume healthy fats to regenerate your cells and promote ketosis. Research shows a high intake of fat on diets like the ketogenic diet help with weight loss and improves health markers, such as blood sugar. More research is needed on fat fasting [7].

However, due to the restrictive nature of this protocol, health professionals don’t advise staying on a fat fast long-term. Without a varied diet, many health experts point to an increased risk of nutrient deficiencies.

Have You Tried a Fat Fast?

How was your experience on a fat fast? Why did you decide to try a fat fast and what were your results?

Steph Green is a content writer specializing in and passionate about healthcare, wellness, and nutrition. Steph has worked with marketing agencies, written medical books for doctors like ‘Untangling the Web of Dysfunction,’ and her poetry book ‘Words that Might Mean Something.’ In 2016, after four years of struggling with her own health problems and painful autoimmune disease, Steph developed a life-changing and extensive knowledge of keto, nutrition, and natural medicine. She continues on her healing journey and enjoys helping others along the way.



Bergqvist, A. G. C., Schall, J. I., Gallagher, P. R., Cnaan, A., Stallings, V. A. (2005). Fasting versus gradual initiation of the ketogenic diet: A prospective, randomized clinical trial of efficacy. Epilepsia, 46(11), 1810-1819.


Paoli, A., Grimaldi, K., Bianco, A., Lodi, A., Cenci, L., & Parmagnani, A. (2012). Medium term effects of a ketogenic diet and a Mediterranean diet on resting energy expenditure and respiratory ratio.BMC Proceedings, 6(3),


Manninen, A. H. (2006). Very-low-carbohydrate and preservation of muscle mass.Nutrition Metabolism (London),


Johnstone, A. M., Horgan, G. W., Murison, S. D., Bremner, D. M., & Lobley, G. E. (2008). Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum. American Journal of Clinical Nutrition, 87(1), 44-55.


Kreitzman, S. N., & Coxon, A. Y., & Szaz, K. F. (1992). Glycogen storage: Illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. American Journal of Clinical Nutrition, 56(1), 292S-293S.


Goday, A., Bellido, D., Sajoux, I., Crujeiras, A. B., Burguera, B., Garcia-Luna, P. P., Oleaga, A., Moreno, B., & Casanueva, F. F. (2016). Short-term safety, tolerability and efficacy of a very low-calorie-ketogenic diet interventional weight loss program versus hypocaloric diet in patients with type 2 diabetes mellitus. Nutrition & Diabetes, 6(9), 

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