Fat fasting is growing in popularity among those who follow the ketogenic diet.
Before we get into the details what the fat fast technique is and how to incorporate it into your keto low-carb lifestyle, let’s quickly look at where it came from.
How Fat Fasting Came to Be
Despite fat fasting gaining a large following in the 21st century, this concept has been around for decades.
Dr. Robert Atkins, the author of the book Dr. Atkins New Diet Revolution, introduced fat fasting to “reset” the body when a weight loss plateau is reached.
The fat fast technique has now been written about rather extensively, with proponents suggesting it has a myriad of benefits for those on the ketogenic diet (when used correctly).
Be careful not to confuse fat fasting with intermittent fasting, as the two are not the same.
If you want to learn more about intermittent fasting, we have a guide you can read by clicking here.
However, if you want to learn about fat fasting, you’ve come to the right place!
What Is the Ketogenic Diet?
Many of you already understand how the keto diet plan works; if not, here’s a quick introduction before we dive into fat fasting itself.
Ketogenic and other very-low-carb diet plans have actually been around for decades. The majority of low-carb diet plans, including the ketogenic diet plan, are great for weight loss and various other health benefits.
In fact, physicians often use the ketogenic diet in patients with conditions such as Parkinson’s disease and Alzheimer’s disease.
It is also useful for treating epilepsy when drugs are not effective. Some evidence suggests that the keto diet may even be a form of reducing the risk of cancer.
Are All Calories Really the Same?
The media and certain nutrition “experts” purport that calories are the all the same regardless where they come from.
This is a woefully short-sighted approach to nutrition, as the food and drink you consume is much more than just the sum of its parts.
For example, a diet that contains 2000 calories purely from simple sugars will have many different effects on the body than an equal-calorie diet containing mostly protein and fats.
The nutrients you eat do a heck of a lot more than merely provide energy to your body.
Nevertheless, to lose weight, the same “golden” rule applies: Move more, eat less, and concentrate on nutrient-dense, wholesome foods.
With that in mind, here is the gist of the ketogenic diet: Greatly limit carbs to a minimal amount while eating ample amounts of healthy fats and moderate amounts of high-quality proteins.
By doing so, your body begins utilizing fat for energy and producing ketones. After a few days of restricting carbohydrates sufficiently, you enter ketosis.
If you want a more comprehensive overview of the ketogenic diet and its benefits, check out our Guide to the Standard Ketogenic Diet.
Overview of Fat Fasting
Fat fasting is a form of fasting typically advised for those who are currently keto-adapted and at a weight-loss plateau.
The protocol of fat fasting entails consuming about 85-90% of your calories from fat while keeping your overall calorie consumption low, generally no more than 1000-1200 calories per day.
We strongly encourage that you follow a fat fast for no longer than 5 days at a time. If you follow a fat fast for any longer, you risk losing significant lean mass and micronutrient deficiencies.
When you begin a fat fast, and you’re currently keto-adapted, your ketone values will likely get extremely high (i.e. higher than 3 mMol/L).
Since the majority of the energy you’re consuming during a fat fast originates from fats, your body initiates lipolysis and begins utilizing fat stores for energy.
Eating Protein During a Fat Fast
Research studies reveal that “basic” fat fasting (90% of total calories from fat) doesn’t have more advantages than a fat fast with lower fat and higher protein.
However, this doesn’t indicate that traditional fat fasting isn’t beneficial. Instead, it just suggests that if you consume a little more protein and a touch less fat, you can attain the same, if not better, outcome.
This is actually an important modification to the fat fast protocol since, per gram, protein is the most satiating macronutrient. Thus, eating a little more protein will help you keep appetite at bay throughout the fasting phase.
For example, sufficient protein consumption from 1000 calorie diet for a typical individual is roughly 15-20% of total calories (physically active individuals and those with less body fat and more lean mass require a bit more).
Because you are consuming around 5% or fewer calories from carbohydrates on a fat fast, you will eat around 75-80% of calories in the form of dietary fats. Not a significant change from a “typical” fat fast.
What Research Says About Fat Fasting
Research studies from the 1950s-1960s demonstrated that fat fasting is ideal for weight loss and maintaining muscle mass when comparing to equal-calorie diets comprised of mostly protein or mostly carbohydrates. [1,2]
However, the findings of these studies appear to be a bit misrepresentative of the benefits of fat fasting due to poor study designs and subjects cheating on their diet.
Curiously though, one study showed that those on a fat fast led to double the weight loss compared to those using a total fast. Those on a total fast lost more muscle mass and minimal body fat. 
While the results were compelling, the study was done on chronically obese subjects who reportedly had exceptionally high energy expenditure.
Protein-sparing nature of low-carb diets
An excerpt from a 2006 meta-analysis published in Nutrition & Metabolism on the protein-sparing nature of very-low-carb diets notes:
“Young et al. compared three diets containing the same amounts of calories (1,800 kcal/day) and protein (115 g/day) but differing in carbohydrate content. After nine weeks on the 30-g, 60-g and 104-g carbohydrate diets, weight loss was 16.2, 12.8 and 11.9 kg and fat accounted for 95, 84, and 75% of the weight loss, respectively.
Importantly, underwater weighing was used to determine body composition. Although these results should be interpreted cautiously given the low number of subjects, this study strongly suggests that a very-low-carb diet promotes fat loss while preserving muscle mass, supporting the notion that ‘a calorie is not a calorie’“.
Keep in mind that prolonged calorie restriction combined with inadequate protein intake can lead to nutrient deficiencies, significant muscle mass loss, and decreased basal metabolic rate (BMR). This is why you shouldn’t do the fat fast for more than five days at a time.
It’s also key to note that no contemporary studies seem to take fat-adaptation (ketosis) into consideration.
The body works much different for those on a higher-carb diet and those on the ketogenic diet. The logical extrapolation is that fat-adapted individuals (or those in ketosis) would experience less muscle tissue loss during a fat fast.
When Is It Time to Consider a Fat Fast
Here are the main guidelines for when you should consider fat fasting:
- If your weight loss stalls for longer than three weeks and you have ruled out all other possible factors. It’s only a natural part of dieting for weight loss that you will reach plateaus where your body weight just doesn’t budge. However, you shouldn’t assume that each time your weight loss stalls, you need to implement fat fasting. Make sure you have everything else dialed in first, such as a proper ratio of nutrients for ketosis and daily calorie deficit. Before trying the fat fast, you might benefit from intermittent fasting instead (you can find our Guide to Intermittent Fasting here).
- If you’re currently in ketosis. Fat fasting will be rather useless if you’re not already following the ketogenic diet. If you’re not currently in ketosis, start by following the ketogenic diet plan for a minimum of three weeks. In this case, only utilize the fat fast protocol if you encounter a weight-loss plateau. You can begin by following our Complete Guide to Losing Weight on the Ketogenic Diet.
- If you had a cheat day (or large cheat meal) and wish to get back into ketosis/on track as quickly as possible. I would personally not utilize the fat fast for this scenario, but rather an intermittent 16-18 hour fast, or simply go back to your routine ketogenic diet and keep active. You’re human, it’s okay to indulge every now and then without feeling like you need to make amends for eating “unhealthy” food.
How to Follow the Fat Fast
Intuitively, the majority of your calories will derive from fat. You need to ensure they contain healthy fats such as monounsaturated fats, omega-3s and medium-chain triglycerides (MCT).
I recommend consulting this guide we have written for the best fat sources when carb intake is limited.
You should also incorporate small portions of high-quality protein sources and fibrous vegetables during a fat fast. Check out our Ketogenic Foods List for which foods are best.
Remember, you should only follow fat fasting for five days maximum; most people should only implement this protocol once a month if necessary.
Tips Prior to Starting Fat Fasting
- Don’t perform any intense workouts during your fat fast. This doesn’t imply that you should remain completely sedentary while fat fasting. In fact, you should still keep active but just stick to light cardio or some easy strength training at home. You should be emphasizing recovery during a fat fast, so resist the urge to go to the gym and obliterate yourself with a grueling workout.
- Preferably, consume a multivitamin or electrolyte supplement daily to make up for any micronutrient deficiencies.
- Use an app, like MyFitnessPal, to help track your calorie/food intake during the fat fast. There’s a strong chance you will eat too much if you’re not diligent about tracking your food intake during a fat fast. After all, 1000 calories isn’t nearly as much as it looks like when you’re eating mostly fat.
Frequent Small Meals vs Fewer Large Meals
Traditional fat fasting, as specified by Dr. Atkins, states you must consume 4-5 smaller meals throughout the day, each consisting of about 20-25% of your total calorie intake. However, this isn’t what research or anecdotes suggest is necessary.
In fact, the evidence I’ve come across contends that meal frequency is nearly irrelevant so long as total energy balance remains the same.
Thus, it might be much easier for you to simply consume 1-2 routine meals rather than stressing about eating every 2-3 hours. This is especially pertinent if you’re already following an intermittent fasting regimen.
Unless you experience chronic hypoglycemia from only eating 2-3 times per day, you do not need to worry about frequently eating throughout the day.
For those of you that prefer having multiple smaller meals during a fat fast, you will benefit by checking out our awesome Fat Bomb Recipes.
Ultimately, you will need to do some trial and error to find out which meal frequency works best for you. Personally, I’ve attempted fat fasting twice (once with 4-5 meals daily and once with 1-2 meals daily).
The outcomes were the same, but I struggled to keep my appetite under control when consuming 4-5 smaller meals throughout the day. I find that the more frequently one eats, the more likely they are to brood over food throughout the day.
Fat Fasting Key Points
- Fat fasting is a technique where you substantially lower calorie intake and eat nearly all of your calories (i.e. 70-80% total daily calorie intake) from dietary fats.
- Fat fasting is generally best for people who are already fat-adapted and in ketosis.
- We advise implementing a fat fast when weight loss on the ketogenic diet stalls for several weeks in a row.
- Fat fasting may be useful after you have a large cheat meal or cheat day.
- You should not follow a fat fast for more than five consecutive days (and no more than once per month).
- It is best to try intermittent fasting first before you consider a fat fast.
- Eating small amounts of protein while fat fasting is key to help reduce cravings and maintain muscle mass.
- Kekwick, A., and Pawan, L.S., “Calorie Intake in Relation to Body Weight Changes in the Obese”, Lancet, 1956 and “Metabolic Study in Human Obesity with Isocaloric Diets High in Fat, Protein and Carbohydrate”, Metabolism, 1957
- Benoit, F.L. et al., “Changes in body Composition During Weight Reduction in Obesity: Balance Studies Comparing Effects of Fasting and a Ketogenic Diet”, Annals of Internal Medicine, 1965
- Jon Schoenfeld, B., Albert Aragon, A., & Krieger, J. W. (2015). Effects of meal frequency on weight loss and body composition: a meta-analysis. Nutrition reviews, 73(2), 69-82.