The ketogenic diet and fasting protocols have one very important thing in common – they train your body to stop relying on glucose and instead burn fat for fuel.
So what happens when you combine the two? Is it metabolic mayhem or a match made in heaven?
In this article, you’ll learn the different types of fasting, what happens when you combine fasting with a keto diet, and whether you should consider trying the combo out for yourself.
The Various Ways To Fast
Many people find that fasting is an excellent way to shed some pounds and gain control over their metabolic health. But what exactly is fasting?
The word “fast” implies going without food for an extended period, but the term is really quite subjective. For someone that’s used to eating every couple of hours, taking a four-hour break from food may feel like a fast. On the other hand, people accustomed to skipping meals may feel like 12 hours without food is nothing.
In the world of dietary approaches, fasting does have some general guidelines, and although there are handfuls of different ways to fast these days, three main categories are as follows:
Intermittent fasting, also referred to as “IF,” is a type of fasting protocol that’s gained a lot of popularity in the last decade as a way to enhance energy, burn fat, and keep your metabolism in check.
There are several different intermittent fasting protocols, but what they all boil down to is creating “eating windows.” Eating windows are periods in your day where you eat while you abstain from food for the rest of the day.
A very popular eating window protocol is called the 16:8 fast, where you fast for 16 hours and keep your eating window within an 8-hour timeframe. For example, you can start your eating window at 10 am and then finish your eating window at 6 pm. This allows a 16-hour period of fasting overnight.
Some people like pushing their intermittent fasts up to 20 or 22 hours, basically just enjoying one meal a day.
Some people like to just bite the bullet and go for a full 24-hour fast instead of creating eating windows. Of course, if you’re a 24-hour faster, you’ll only choose a couple of days per week to fast, as opposed to creating regular eating windows.
Some people go the alternate-day fasting route, where they fast every other day.
This option can be helpful for people who enjoy the benefits of fasting but don’t like sticking to a regular protocol. The secret to 24-hour fasting is that you can arrange it so that you never have a full day without food. For example:
If you start your fast on Monday at 4:00 pm and then break your fast on Tuesday at 4:00 pm, you still get to eat breakfast, lunch, and a snack on Monday, and you can enjoy an early dinner on Tuesday.
Pro tip: make sure you break your 24-hour fast with a meal that’s nourishing as opposed to binging on pizza and ice cream. You want to gain all the benefits of fasting without putting your poor digestion in shock.
Prolonged fasting is considered anything over a 24-hour fast. This could be 36 hours up to several days (or even weeks). Extending your fast for a few days can produce some really great results, but it’s always recommended that you consult with a healthcare professional if you’re planning on giving extended fasting a try.
Fasting and The Keto Diet: Similarities and Differences
As mentioned, the primary similarity between the ketogenic diet and fasting is that both protocols train your body to burn fat for fuel rather than relying primarily on glucose.
So, what’s the difference?
When you fast, your body has no choice but to tap into your energy stores because you’re not consuming any new energy. Your body stores energy in two ways; glycogen in your liver and muscles and fat in your fat cells.
Once you’ve used up any nutrients that are floating around in your blood, your body sets its sights on your stored glucose. While most people have a fair amount of stored glucose, there isn’t an endless supply, and it doesn’t take too long before your body decides to diversify its energy sources and start breaking down body fat.
This is when the process of ketogenesis begins. As glucose stores become more and more depleted, ketones take over as the primary fuel source for your body. Once ketone levels reach a certain threshold, you’re officially in a state of ketosis.
On a keto diet, a similar process takes place – with one big difference. Instead of abstaining from food altogether, the keto dieter will simply avoid carbohydrates. On keto, you don’t have to reduce food or calorie intake at all; limiting carbohydrates is enough to help you burn through stored carbs and eventually start tapping fat stores to make ketones. It’s the same result, with a slightly different approach.
Is Fasting Easier When You Follow A Keto Diet?
Many people that follow a low carbohydrate diet enjoy throwing in a fast here and there to really pump up ketone production. Fasting is, in fact, easier when you follow a keto diet for a few reasons:
#1. The biggest barrier to entry when it comes to fasting for most people is the fear of hunger. Generally speaking, when you’re running on ketones, you don’t experience hunger in the same way. Some people feel like they lose their appetite altogether, while others notice huge shifts in cravings.
This means that if you’re following a keto diet, you’ll already feel less of a pull toward food, which makes the idea of going without food much easier.
#2. The second most significant barrier to entry for many people that want to try fasting is concern around energy. If you’re someone that’s used to running on carbs and then all of a sudden you stop fueling yourself with glucose, your body is going to feel it.
It can take several days, if not weeks, for your body to become keto-adapted. Once keto-adapted, however, you’ll have a steady stream of energy coming from ketones.
For a keto dieter, going without food for a day isn’t that big of a deal because their body is primed to tap into their fat stores and produce ketones – they don’t miss a beat. This means they get to experience steady energy whether they’re eating meals or not.
#3. Another downside of fasting that people don’t always consider is the immediate pushback that your body starts to feel when it hasn’t gotten its food fix. Even shorter fasts (like 12 hours) can result in headaches, brain fog, and moodiness – also known as “hanger.”
Both fasting and ketosis can cause something called “keto flu,” which is basically a cute name for the host of uncomfortable symptoms that come along with the process of keto-adaptation.
For someone who is keto-adapted, these side effects of fuel restriction are a thing of the past. Their body has already become adapted to living off ketones, so they don’t have to go through the uncomfortable transition phase of becoming fat-adapted. They have steady energy levels and a controlled appetite and don’t get headaches or other signs of low blood sugar levels when they go without food for prolonged periods.
So, why would you combine fasting with the keto diet if they do the same thing for your metabolism? When you fast, you’re basically supercharging your low carb diet. You produce more ketones and get to tap even deeper into your fat stores (for more fat burning). As a result, metabolic processes like weight loss and autophagy (clearing out old cells) are increased.
Furthermore, research shows that fasting when exercising can enhance overall endurance and improve muscle mass synthesis.
Following a low-carb, high-fat diet comes with its own host of health benefits, but adding in intermittent fasting can supercharge your results.
These two eating styles really work great together as being keto-adapted can help reduce the barriers to entry for fasting, and fasting can help you get into ketosis faster. It’s a win-win.
Intermittent fasting works best for beginners that want to dip a toe because this eating pattern is more flexible than 24-hour fasting or prolonged fasts. The short-term commitment typically makes IF people first stop when trying out fasting.
Adding fasting to your keto diet plan can also make things easier as you don’t have to plan as many meals. Some people find that making a keto meal plan is the most challenging part of the diet — so fasting can help simplify things a bit.
- Masood, Wajeed, Pavan Annamaraju, and Kalyan R. Uppaluri. "Ketogenic diet." StatPearls [Internet] (2021).
- Roekenes, Jessica, and Catia Martins. "Ketogenic diets and appetite regulation." Current Opinion in Clinical Nutrition & Metabolic Care 24.4 (2021): 359-363.
- Liśkiewicz, Daniela, et al. "Upregulation of hepatic autophagy under nutritional ketosis." The Journal of Nutritional Biochemistry 93 (2021): 108620.
- Dashti, Hussein M., et al. "Long-term effects of a ketogenic diet in obese patients." Experimental & Clinical Cardiology 9.3 (2004): 200.
- Harber, Matthew P., et al. "Muscle protein synthesis and gene expression during recovery from aerobic exercise in the fasted and fed states." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 299.5 (2010): R1254-R1262.
- Van Proeyen, Karen, et al. "Beneficial metabolic adaptations due to endurance exercise training in the fasted state." Journal of applied physiology (2011).