The ketogenic diet and intermittent fasting are two different dietary strategies that have a lot in common. Both boost ketones and both make the body burn fat. When used together, they definitely make a powerful tandem.
In fact, you'll see keto dieters everywhere using these dietary strategies simultaneously to boost weight loss, tackle plateaus, increase energy, and some use them to increase longevity. They're not wrong for doing so because these benefits were scientifically proven to be true.
In this article, we explain how intermittent fasting and keto work in synergy to boost weight loss and improve health. We will also shortly explain how you can incorporate intermittent fasting into your keto diet. But first, let's explain what keto and intermittent fasting are and how they work individually.
The ketogenic diet is a strict low-carb, high-fat diet. The main purpose of this diet is to induce ketosis – a metabolic state where the body goes from burning glucose to burning fat for fuel.
The reason why your body burns fat in the absence of glucose is to provide energy for your cells but also to produce ketones, mostly to fuel your brain. Ketones are water-soluble molecules that replace glucose when carb intake is low. You can read more about them here.
The main benefit of this diet is weight loss. Other keto benefits include the following:
Researchers originally designed the keto diet to treat epilepsy in children. The idea came to be somewhere in the 1920s. Back then, studies found that a diet high in fat and low in carbs causes elevated ketones and that a ketone-fueled brain had fewer seizures .
Over the next few decades, researchers discovered that keto diets provide benefits beyond epilepsy control . These days, wellness enthusiasts across the globe are wholeheartedly embracing the ketogenic diet. However, most are using the diet to lose weight and to control diabetes (it is a low-carb diet after all).
Studies show that low-carb and keto diets are more effective for weight loss than classic calorie reduction or low-fat diets [3, 4]. These diets are also easier to stick to because they suppress appetite. Just think about it – no more sugar crashes or carb cravings and plenty of fat to keep you feeling full and satisfied.
If you want to learn more about the ketogenic diet, read our comprehensive overview here.
Intermittent fasting is all about when you eat instead of what you eat.
It is a dietary strategy based on the timing of food intake rather than on restricting calories or eating specific food. During intermittent fasting, you fast and eat within specific windows of time. For example, skipping breakfast and having your next meal in the evening constitutes intermittent fasting.
There are many different types of intermittent fasting, but the most common three include the following:
We already mention this one. You can skip any meal you want. Some people prefer skipping breakfast, while others prefer skipping lunch. You can also skip dinner for a overnight fast.
This is the most popular approach to intermittent fasting. It involves restricting food intake during specific eating windows. People often refer to specific eating windows with numbers like 16/8 (16 hours of fasting and an 8-hour eating window).
This approach involves fasting for a few days every week and eating regular meals other days of the week. This is the most difficult approach.
The whole point of intermittent fasting is to reduce the amount of food you eat in a single day. When you eat, you can only take in a limited amount of food. By restricting your feeding windows, you'll eat much less than you would with three meals a day plus snacks in between.
Another reason people fast intermittently is because it boosts fat burning. When you're in a fasted state instead of a fed state, your body is forced to burn fat stores to give you energy. In the process, it starts turning fat into ketone bodies to fuel the brain and other organs. The ketogenic diet mimics fasting in that way, but you also don't feel hungry on a keto diet.
Cultures globally have been using fasting as part of spiritual practice and alternative medicine for millennia. Even Hippocrates, the father of modern medicine, prescribed fasting as the number one treatment option for almost anything. One of his most famous quotes clarifies the wisdom behind fasting:
"Our food should be our medicine. Our medicine should be our food. But to eat when you are sick is to feed your sickness."
Nowadays, researchers examining the effects of fasting on human health also came to the conclusion that an occasional fast is good for us . So far, studies show that calorie restriction (like during fasts) without malnutrition is the only approach proven to make animal models live longer.
And when speaking of calorie restriction, this is the main reason why fasting works. Overeating causes obesity, diabetes, high cholesterol, and heart disease – all diseases plaguing today's world. Fasting works simply because it causes changes in metabolism and biochemical processes on the cellular level .
When you eat more food than your body needs for energy production, the pancreas releases insulin. Insulin then signals your body's fat cells to store the extra calories as fat for later use. The opposite happens when you don't eat – your insulin levels drop and this signals fat cells to release the stored fat. In other words, fasting allows your body to use up stored fat for energy (that's why we got those fat stores in the first place).
Our bodies exist in two metabolic states: fed and fasted. The fed state is when blood glucose levels are high while the fasted state is when blood glucose levels are low. Glucose levels rise and drop depending on our carbohydrate intake mainly. This is because our bodies are used to running on glucose rather than fat or protein.
But besides boosting fat burning and weight loss, intermittent fasting also improves overall health. Researchers say this happens because our cells are under "stress" during fasting and they respond to this stress adaptively by enhancing their ability to cope with it making them more resistant to diseases .
Researchers also say that taxing the body from time to time is essential for it to become sturdy. As long as you give your body time to recover (like during your feeding window), fasting will pose no harm and, in fact, make you stronger.
Intermittent fasting and keto affect the metabolism in the same way (i.e. both lead to ketosis), so why not just use one or the other? Well, for practical reasons. Intermittent fasting is difficult when you're not on a ketogenic diet and the ketogenic diet gets a boost with intermittent fasting.
Keto dieters who are well into ketosis already have low blood glucose and insulin levels and are in full fat-burning more. They also have reduced appetite thanks to the satiating effects of a keto diet as well as elevated ketone levels. All this means that they'll experience less hunger and no sugar crashes when fasting.
If you're on a standard high-carb diet, not eating for long periods of time will cause sharp drops in blood glucose levels and a rise in hunger hormones. This can have you feeling shaky, weak, and irritable. Not to mention that it's impossible to function when feeling hungry all day.
And as for the benefits of intermittent fasting on ketosis – it works. Intermittent fasting helps raise ketone levels by keeping insulin levels low. Elevated ketones mean your body is burning fat for fuel. Furthermore, intermittent fasting allows you to reduce your calories even more while on a keto diet because you spend less time eating.
Intermittent fasting and autophagy are two terms you'll often see mentioned in the same context. Autophagy is a normal metabolic process where a cell devours itself and recycles what's left for making new cells or maintaining energy . It's essentially our body's recycling program.
During intermittent fasting, autophagy is upscaled. In fact, it is upscaled anytime your body is under stress and during low food intake. This happens because your body is trying to preserve energy when nutrients are low.
Although autophagy sounds scary, it really is completely normal and necessary even. Your body turns over redundant or damaged cells and proteins as well as soluble protein thanks to autophagy. Recent studies even show that low levels of autophagy speed up aging .
Studies also show that fasting increases autophagy of nerve cells proving that this metabolic process protects brain health . Fasting-induced autophagy also kills cancer cells according to research studies .
Now that you know how and why intermittent fasting works, you also want to know the benefits. From greater weight loss to disease prevention, there are many benefits to periodic food restriction. Here are just a couple of those for you to take note of:
Most people use intermittent fasting for weight loss. In combination with a keto diet, it's an effective tool in shedding excess body fat. Intermittent fasting works for weight loss because it:
Intermittent fasting also increases your basal metabolic rate – the rate at which your body burns calories during rest. Researchers believe this happens because fasting causes a rise in a hormone called norepinephrine which seems to alter metabolism into fat-burning mode .
On the other hand, simple low-calorie diets do the exact opposite – they lower your metabolic rate. One study on obese subjects found that their metabolic rate dropped when eating a low-calorie diet even during exercise . On low-calorie diets, the body simply tries to preserve energy by lowering the metabolic rate, and this, unfortunately, stalls weight loss.
Luckily, intermittent fasting doesn't do that. You eat enough food during feeding windows, so your body has no need to slow down metabolism. According to a 2014 studies review, intermittent fasting causes weight loss of up to 8% over a 3-24 week period  — that’s a lot of weight to lose in such a short time frame.
A diet high in refined carbs causes blood sugar spikes and low-grade inflammation – both of which negatively affect your brain. Even researchers agree that the typical "Western diet" high in refined carbs cause degradation of the hippocampus – the memory center of your brain .
Sure, your brain runs on carbs and there's nothing wrong with that. But why wouldn't it run on ketones? After all, there's plenty of research evidence that diets that increase ketone levels improve mental functioning . This is because ketones don't lead to inflammation and have a protective effect on nerve cells.
However, there's another reason why intermittent fasting combined with a keto diet boosts mental acuity. Fat provides a more powerful and constant source of fuel for your brain. Your brain uses up glucose fairly quickly. Ketones, on the other hand, are a more efficient fuel, providing more energy per unit oxygen used .
Animal studies found that intermittent fasting increases the number of brain cells [17, 18]. Studies also show that intermittent fasting increases the production of brain-derived neurotrophic factor (BDNF) . BDNF makes brain neurons more resistant to dysfunction and degeneration.
You probably think that it's counterintuitive to fast when trying to gain muscle. After all, muscles need a constant supply of protein and glucose, right? Well, not necessarily. According to studies on athletes, fasting helps athletes lose body fat while preserving their muscle mass when done right.
For example, one study examined the effects of a 16/8 fast on athletes and found that they lost body fat but retained their muscle mass after 8 weeks of being on the diet . As long as you eat enough macros during your feeding windows, there's no reason why you couldn't fast and exercise at the same time.
In fact, studies on the effects of fasting on exercise performance and muscle synthesis show that it can have favorable effects. For example, having a protein-carbohydrate drink after resistance exercise in a fasted state causes greater muscle building than when the same drink is taken in a non-fasted state .
And if you want to lose weight through exercise, then fasting before a workout is your best bet. There's evidence that training in a fasted state stimulates metabolic adaptations in muscle cells so that they produce energy through fat burning .
Intermittent fasting reduces oxidative stress and low-grade inflammation. Both are key drivers of diseases like diabetes, atherosclerosis, cancer, and autoimmune disorders. Both also lead to faster aging.
Intermittent fasting lowers fights inflammation by lowering high blood glucose — a known trigger of systemic inflammation. In fact, inflammation is the main reason why people with type 2 diabetes and obesity are so prone to developing comorbid conditions.
Another reason fasting reduces inflammation is because it boosts ketone production. Studies on ketones found that they show an anti-inflammatory effect. One particular study on mice from 2015 found that fasting boosts the production of hydroxybutyrate – an important ketone body that inhibits inflammasome – proteins that cause inflammation .
There's also evidence that fasting makes the body more resistant to oxidative stress . Oxidative stress is an imbalanced state in which your body's defense against free radicals is compromised. This can happen when you're ill or eat a high-carb diet.
If your goal is to live to be a hundred, then occasional fasting is a must. We already explained that animal studies found that calorie restriction was the only proven way to increase life expectancy. This is partially the direct effect of autophagy as already explained.
Studies show that fasting has a similar effect as calorie restriction when it comes to longevity . Fasting improves overall health by balancing blood glucose, reducing inflammation, and improving free radical defense. It shouldn't come as a surprise that it also boosts longevity.
Living proof that fasting or calorie restriction, if you will, boosts longevity are people of Okinawa. Okinawa has one of the highest numbers of centenarians in the world. Their traditional diet is dense in nutrients but low in calories. Unfortunately, Westernization has changed the eating habits of younger Okinawans and this has shortened their life expectancy .
Okinawans traditionally ate around 11% fewer calories (1,800 calories per day) than normally recommended. However, keep in mind that diet is probably not the only reason why Okinawans live such long, healthy lives. Climate and lifestyle can also play a role, but diet is, nevertheless a leading factor.
There's not much planning or that many technicalities involved in intermittent fasting. You simply have to not eat for a period of time. Which fasting method you should use is completely up to you. As long as you stay within your recommended daily macros or go a bit below them (15-30%), you're fine.
If you plan to make two-windows, then it's best to stick to them during your fasting days. This will allow your body to make metabolic adjustments and anticipate food intake at the same time each day. Remember, we are creatures of habit and our body loves routine.
To break your fast, make sure to eat slowly to avoid overeating. Or even better, plan your meals. Calculate your daily macros and calories for the day and make your meals accordingly. And don't think that a cup of coffee won't break your fast. Anything with calories in it is bound to break a fast.
We suggest drinking keto coffee with MCT oil in the morning, and having your first meal in the evening. MCT Oil helps boost ketone production and will give you sustained energy when combined with coffee. It's also helpful if you're just starting a keto diet and need something that will get you quicker into ketosis.
If you're pregnant or breastfeeding, intermittent fasting is not for you. A study examining the effects of Ramadan fasting on quality of breastmilk found that it was deficient in important micronutrients, namely zinc, potassium, and magnesium . Fasting during pregnancy also puts babies at risk of nutrient deficiencies.
If you're diabetic, you'll have to be careful with fasting. Make sure to monitor your blood glucose levels and speak to your doctor about making medication adjustments. They may have to change your insulin dose since fasting strongly impacts blood glucose levels.
other thing to keep in mind when fasting is your fluid and electrolytes intake. Although some people avoid taking in anything during fasting, it's best to drink fluids to stay healthy and functioning. This is especially true if you're working, highly active, and during summer.
And lastly, don't be hard on yourself. Fasting is difficult, but it shouldn't be unbearable. If you feel weak, miserable, shaky, and foggy during your fast, it may be time to break it. Or you can simply shorten your fasting windows. There's really no point to fasting if it's making you miserable. After all, a keto diet will give you the same benefits of fasting but without the hunger.
Intermittent fasting and keto compliment each other perfectly for more efficient weight loss, ketone production, and overall health. However, you can do one without the other. It's simply that they're often used in conduction due to their shared benefits and metabolic effects.
If you plan to fast intermittently, do so when already in ketosis. This will help you get through your fast with ease since your body is already utilizing fat for fuel - no need to refeed on carbs all day. Also, make sure to pick one of the three fasting methods that best suits your needs and limits.
Keep in mind that intermittent fasting doesn't work for everyone. It may or may not help you reach your goals. But giving it a shot can prove worthwhile in the long-run, especially for your overall health and longevity.
If you want to learn more about keto fasting, read our article covering its many benefits practical tips here. We also suggest enrolling in our free Ketocademy course if you're new to the keto diet and want to learn more on how to get started.