Keto Intermittent Fasting: How It Relates to a Keto Diet
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Keto Intermittent Fasting: How It Relates to a Keto Diet

Ketosis and fasting often come up in the same conversation. Learn about ketosis and intermittent fasting so you no longer confuse one for the other.

Keto Intermittent Fasting

The topics of ketosis and intermittent fasting are closely related and often fall within the same conversation. That’s because fasting can be a useful practice to help you reach ketosis. But is there such a thing as keto intermittent fasting?

Just as intense and prolonged exercise (particularly HIIT training or lifting weights) may help induce a ketogenic state, intermittent fasting can help you enter ketosis faster than following a keto diet alone.

There are many more overlaps between intermittent fasting and a low-carb diet, which you’ll learn about in this guide.

What Is Ketosis?

Ketosis is the process of burning ketone bodies for energy.

On a regular diet, your body burns glucose as its primary fuel source. Excess glucose is stored as glycogen. When your body is deprived of glucose (due to exercise, intermittent fasting, or a ketogenic diet), it will turn to glycogen for energy. Only after glycogen is depleted will your body start burning fat.

A ketogenic diet, which is a low-carb, high-fat diet, creates a metabolic shift that allows your body to break down fat into ketone bodies in the liver for energy. There are three main ketone bodies found in your blood, urine, and breath:

  • Acetoacetate: The first ketone to be created. It can either be converted into beta-hydroxybutyrate or turned into acetone.
  • Acetone: Created spontaneously from the breakdown of acetoacetate. It’s the most volatile ketone and is often detectable in the breath when someone first goes into ketosis.
  • Beta-hydroxybutyrate (BHB): This is the ketone that’s used for energy and the most abundant in your blood once you’re fully in ketosis. It’s also the type found in exogenous ketones and what ketogenic blood tests measure.

Intermittent Fasting and Its Relation to Ketosis

Intermittent fasting consists of eating only within a specific period of time and not eating for the remaining hours of the day. Every person, whether they’re aware of it or not, fasts overnight from dinner to breakfast.

The benefits of fasting have been used for thousands of years in Ayurveda and Traditional Chinese Medicine as a way to help reset your metabolism and help your gastrointestinal system after overeating.

There are many approaches to intermittent fasting, with different time frames:

  • 16-20 hours fasting period
  • Alternate-day fasting
  • 24-hour day fasting

If you want to start fasting, one popular version is the 16/8 keto intermittent fasting method, where you eat within an 8-hour eating window (for example, 11 a.m. to 7 p.m.), followed by a 16-hour fasting window.

Other fasting schedules include the 20/4 or 14/10 methods, while some people prefer doing a full 24-hour fasting day once or twice per week.

Intermittent fasting can put you in a state of ketosis faster because your cells will quickly consume your glycogen stores, and then start using your stored fat for fuel. This leads to an acceleration of the fat-burning process and increased ketone levels.

Ketosis vs. Intermittent Fasting: Physical Benefits  

Both the keto diet and intermittent fasting can be effective tools for:

  • Healthy weight loss
  • Fat loss, not muscle loss
  • Balancing cholesterol levels
  • Improving insulin sensitivity
  • Keeping blood sugar levels stable

Keto for Weight Loss, Fat Loss and Improved Cholesterol

The keto diet drastically decreases your carb intake, forcing your body to burn fat rather than glucose. This makes it an effective tool not only for weight loss, but also for the management of diabetes, insulin resistance, and even heart disease[*][*][*].

Keto Intermittent Fasting: Weight Loss Benefits

While individual results vary, keto has consistently led to a reduction in weight and body fat percentage in a wide range of situations.

In a 2017 study, participants who followed a low-carbohydrate keto meal plan significantly decreased body weight, body fat percentage, and fat mass, losing an average of 7.6 pounds and 2.6% body fat while maintaining lean muscle mass[*].

Similarly, a 2004 study observing the long-term effects of a keto diet in obese people found that their weight and body mass decreased dramatically over the course of two years. Those who drastically reduced their carbohydrate intake saw a significant decrease in LDL (bad) cholesterol, triglycerides, and improved insulin sensitivity[*].

In 2012, a study compared a ketogenic diet to eating fewer calories in obese children and adults. The results showed children following the keto diet lost significantly more body weight, fat mass, and total waist circumference. They also showed a dramatic decrease in insulin levels, a biomarker of type 2 diabetes[*].

Intermittent Fasting for Fat Loss and Maintaining Muscle Mass

Research has shown that intermittent fasting can be an efficient weight loss tool, sometimes being even more useful than simply restricting your calorie intake.

In one study, intermittent fasting was shown to be as effective as continuous calorie restriction in fighting obesity. In studies done by the NIH, weight loss was reported for over 84% of the participants — no matter which fasting schedule they chose[*][*].

Like ketosis, intermittent fasting can promote fat loss while maintaining lean muscle mass. In one study, researchers concluded that people who fasted had better weight loss results (while preserving muscle) than those who followed a low-calorie diet, even though the total caloric intake was the same[*].

Ketosis vs. Intermittent Fasting: Mental Benefits

Beyond their physiological benefits, both intermittent fasting and ketosis provide various mental benefits. Both have been scientifically shown to[*][*]:

  • Boost memory
  • Improve mental clarity and focus
  • Prevent neurological diseases including Alzheimer’s and epilepsy

Keto for Improving Brain Fog and Memory

On a carb-based diet, the fluctuations in your blood sugar levels can cause fluctuations in energy levels — these are known as sugar highs and sugar crashes. In ketosis, your brain uses a more consistent source of fuel: ketones from your fat stores, resulting in better productivity and mental performance.

This is because your brain is the most energy-consuming organ in your body. When you have a clean and consistent energy supply from ketones, this can help your brain function in a more optimal way[*].

On top of that, ketones are better at protecting your brain. Studies show that ketone bodies may have antioxidant properties that protect your brain cells from free radicals, oxidative stress, and damage[*].

In one study performed on adults with impaired memory, the rise of BHB ketones in their blood helped improve cognition[*].

If you have a hard time staying focused, your neurotransmitters may be to blame. Your brain has two main neurotransmitters: glutamate and GABA.

Glutamate helps you form new memories, learn complicated concepts, and helps your brain cells to communicate with each other.

GABA is what helps control glutamate. Glutamate can make your brain cells overly excited. If this happens too often, it can cause brain cells to stop working and eventually die. GABA is there to control and slow down glutamate. When GABA levels are low, glutamate reigns free and you experience mental fog[*].

Ketone bodies help to prevent brain cell damage by processing excess glutamate into GABA. Since ketones increase GABA and decrease glutamate, they aid in preventing cell damage, avoiding cell death, and improving your mental focus[*].

In other words, ketones help keep your GABA and glutamate levels balanced so your brain stays sharp.

Intermittent Fasting Effects on Stress Levels and Cognitive Function

Fasting has been shown to improve memory, reduce oxidative stress, and preserve learning capabilities[*][*].

Scientists believe that intermittent fasting works by forcing your cells to perform better. Because your cells are under mild stress while fasting, the best cells adapt to this stress by enhancing their own ability to cope, while the weakest cells die. This process is called autophagy[*].

This is similar to the stress your body undergoes when you hit the gym. Exercising is a form of stress your body endures to improve and get stronger, as long as you rest enough after your workouts. This also applies to intermittent fasting and as long as you continue to alternate between regular eating habits and fasting, it can continue to benefit you.

All of this means the keto intermittent fasting combination is powerful and can help improve your cognitive function, thanks to the protective and energizing effects of ketones as well as the mild cellular stress caused by fasting.

The Keto Intermittent Fasting Connection

The ketogenic diet and intermittent fasting share many of the same health benefits because both methods can have the same result: a state of ketosis.

Ketosis has many physical and mental benefits, from weight and fat loss to improved stress levels, brain function, and longevity.

However, it’s important to keep in mind that if you take a milder approach to keto intermittent fasting — for example, eating within an 8-hour window — you probably won’t enter ketosis (especially if you eat a high amount of carbs during that window).

Not everyone who tries intermittent fasting aims to enter ketosis. In fact, if someone who fasts also eats high-carb foods, there’s a very good chance they’ll never enter ketosis.

On the other hand, if ketosis is the goal, you can use keto intermittent fasting as a tool to get there and improve your overall health.

If you’re new to the keto world and would like some helpful tips about how to start, here are a couple of beginner’s guides to help you with your first steps:

If you’re not sure about what kind of dishes you can have on keto, here are a few mouth-watering recipes to add to your diet plan:

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29 thoughts on “Keto Intermittent Fasting: How It Relates to a Keto Diet

  1. Okay so what if you followed the intermittent fasting ‘example’ schedule of eating 12-8pm (or any 8 hr window) and the diet you followed during that time period was Ketogenic, so combining both methods?

      1. Sugar of any amount would break the fast. So far only water, some herbal teas and black coffee are the only things known to not break a fast. Products such as bullet proof coffee are keto diet friendly, but definitely not fasting friendly.

  2. I’m a diabetic and today my glucose level is 245. I’m wondering if I can still go into ketosis with my blood sugar at 245. I am weaning off my insulin in hopes of reversing my diabetes through either a ketogenic diet or intermittent fasting. Your help is appreciated.

      1. Bone broth contains calories and will cause a digestive reaction, which would break the fast. However water, black coffee and most tea (nothing added) would be fine.

  3. So when does ketosis really begin, do you know? I have done countless hours of research on this, and I find sources that say ketosis begins after 6 to 8 hours of fasting, and other sources say it begins after three days of fasting for men. That is a huge discrepancy. Does anyone have any real idea?

    1. It’s very individual, you have to see for yourself. It all depends on how much glycogen do you have stored in your body.

    2. Your body will fully switch to “fasting” ketosis after about 72 hours of no food. The same can be said of the lower level ketosis that is obtained via the keto diet as long as you are keeping the carbs under 20 grams a day during those three days and using exercise to burn off excess glucose stores. What you read about online in terms of 6 to 8 hours after eating is talking about the body the fact that digestion, depending on what and how much you eat, takes about 8 to 12 hours. After digestion is finished the body will begin the process of ketosis and after 72 hours glucose levels will continue to drop while ketone levels will rise. So in short, to be fully in a state of ketosis will take about 72 hours, maybe less or more depending on each person’s ability to switch. Keto adapted individuals can make the switch more easily than those who are not.

  4. I have been following the ketogenic lifestyle for 9 months and have begun Intermittent fasting 23/1 for two weeks. Surprisingly I do not feel hungry and feel compelled to see if I can fast further to 48 hours and see what happens. My glucose level is 54 and my ketones are just 1.1.

    I am drinking water and chaga tea only. Will I be breaking the fast if I take e-lyte sport electrolyte concentrate to replenish my electrolytes?

  5. Not to sound too ignorant after reading all this but if I’m trying to adhere to a ketogenic diet then fasting should get me there quicker, correct? Once you are in ketosis for a long period you no longer need to fast? Is the 16/8 only for fasting or do many on a ketogenic diet still adhere to this type of schedule?

    1. Hey Sam, no ignorance at all! All questions welcome :). It all depends on your goals here and how you feel. Many people find that they are less hungry when following a ketogenic lifestyle and being in ketosis so they end up fasting without even thinking about it. For example, I “fat fast” during the week by only having coffee with mct powder in the morning and then lunch around 2 p.m.. On weekends I like to enjoy brunch so I don’t usually fast then. It all depends on what works for your lifestyle and what your goals are!

  6. I have just started intermediate fasting, 16/8, for a week now and I feel great. I am curious if I can implement a ketones supplement (like the Perfect Keto) into this, and if so, is it something I would add into the 8 hour eating time or can/should it be used during the fasting time?

    1. Josh, you can definitely implement the ketone supplement to help you during or fast or as another source of fuel during your eating window.

  7. I’ve been eating within a 4-5 window for the past two months and not only have I lost about 15 pounds without really needing it but I have really noticed a huge difference in body composition, I’m much leaner and toned then I have been before at the same weight. I don’t have many restrictions for my diet except no processed foods and low sugar. During my fast I only drink water, flat and sparkling with no flavor and black coffee. I honestly love eating this way, it’s so easy and I’m saving myself some money on food.

  8. I have been fasting for four days now and I feel pretty good. I know I am going to make it another two days.But I think I like fasting for the first time ever. I do it mostly for religious purpose along with prayer

  9. Things you can have during IF:
    – Lots of water!
    – Black coffee (no sugar or creamer)
    – Tea (no sugar or creamer)
    – Apple cider vinegar

    1. As long as you eat low carbs and you count your macros properly, you won’t be out of ketosis. You can do intermittent fasting on keto but be sure to still get nutritious ketogenic foods to make sure you’re getting sufficient nutrition. You can check our this article for more info.

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