The topics of ketosis and intermittent fasting often fall within the same conversation. Why? Because intermittent fasting can be used as a tool to reach ketosis.
When you fast, you deplete your body of glycogen stores. Once glycogen stores are gone, fat stores are released into your bloodstream to be converted into energy molecules (ketones) in the liver.
This is the metabolic process we call ketosis.
Just as intense and prolonged exercise (particularly HIIT training or lifting weights) can help induce a ketogenic state, intermittent fasting will make you enter ketosis faster than following a keto diet alone.
There are many more overlaps between intermittent fasting and keto, which you’ll learn about below.
- What Is Ketosis?
- What Is Intermittent Fasting And How Does It Relate To Ketosis?
- Ketosis vs. Intermittent Fasting: Physical Benefits
- Ketosis vs. Intermittent Fasting: Mental Benefits
Ketosis is the process of burning ketone bodies for energy.
On a regular carb-based diet, your body burns glucose, not ketones, 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: It’s the ketone that’s created first. 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 on the breath when someone first goes into ketosis.
- Beta-hydroxybutyrate (BHB): This is the ketone that’s actually used for energy and the most abundant in your blood once you’re fully into ketosis. It’s the type that’s found in exogenous ketones and what blood tests measure.
Now, how does intermittent fasting fit into ketosis?
Intermittent fasting consists of eating within a specific feeding window and not eating the remaining hours of the day. Every person, whether they’re aware of it or not, fasts overnight from dinner to breakfast, for example.
There are many approaches to intermittent fasting — some people fast for 16-20 hours periods, on alternate days or following a 24-hour day fast.
If you want to start fasting, one popular version is the 16/8 method, where you eat within an 8-hour eating window (ex. 11:00 a.m. to 7:00 p.m.), followed by a 16-hour fasting window.
Other fasting schedules include the 20/4 or 14/10 methods. Others practice 24-hour fasts once or twice per week.
Intermittent fasting can put you in ketosis faster because your cells will quickly consume your glycogen stores and start burning fat for fuel.
But what about after you get into ketosis? Is intermittent fasting worth doing consistently?
Short answer: Yes. Here’s why it can be a great addition to your health toolbox:
Both the keto diet and intermittent fasting are 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 ketogenic diet drastically decreases your carb intake, forcing your body to burn fat rather than glucose, making it an effective tool for weight loss.
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, subjects 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 ketogenic diet in obese patients found that weight and body mass of the patients 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 intermittent fasting can be an efficient weight loss tool and sometimes more effective than simply cutting calories.
In one study, intermittent fasting was shown to be as effective as continuous calorie restriction in fighting obesity[*]. In studies done by the NIH, there was reported weight loss with over 84% of participants — no matter which fasting schedule they chose[*].
Like ketosis, intermittent fasting increases fat loss while maintaining lean muscle mass. In one study, researchers concluded that fasting resulted in greater weight loss (while preserving muscle) than a low-calorie diet, even though the total caloric intake was the same[*].
The bottom line is, if you’re trying to lose fat, doing ketosis and IF can be a huge help. But that’s not where the benefits stop.
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 (known as 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.
Why? Because your brain is the most energy-consuming organ in your body. When you have a clean and consistent energy supply from ketones, your brain functions better.
On top of that, ketones are better at protecting your brain.Studies show ketone bodies may have antioxidant properties that protect your brain cells from free radicals, oxidative stress and damage[*].
Glutamate helps you form new memories, learn complicated concepts and gets your brain cells to communicate with each other. Any time you text, talk or think, you can thank glutamate for helping.
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.
What does this have to do with ketones? Ketones prevent damage to brain cells 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 improve your memory, reduce oxidative stress, and preserve your learning capabilities[*].
Scientists believe this happens because IF forces 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 is similar to the stress your body undergoes when you hit the gym. Exercise 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 for intermittent fasting: As long as you continue to alternate between regular eating habits and fasting, it will continue to benefit you.
All of this means both ketosis and IF 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 Perks Of Fasting And Doing Keto
The ketogenic diet and intermittent fasting have many of the same health benefits. Why? Because both methods can have the same result: a metabolic state known as ketosis.
Ketosis has many physical and mental benefits, from weight and fat loss to improved stress levels, brain function, and longevity.
Does intermittent fasting always cause ketosis? Absolutely not. If you take a more mild approach to 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).
Plus, not everyone who tries intermittent fasting aims to enter ketosis. If someone who fasts also eats high-carb foods, there is a very good chance they’ll never enter ketosis.
If, on the other hand, ketosis is the goal, ketoers can use intermittent fasting as a tool to get there and improve their overall health.
Dr. Anthony Gustin is a board-certified sports chiropractor, functional medicine practitioner, entrepreneur, podcast host, and founder of Perfect Keto.
Over the last few years, he has treated thousands of patients with movement rehab, internal diagnostics, and natural interventions, including NFL, MLB and NBA champions. After growing his sports rehab and functional medicine clinics to six locations in San Francisco, he shifted his mission to help as many people as possible achieve optimal health and well-being.