People who should NOT fast include those who are underweight or have eating disorders such as anorexia, women who are pregnant or breastfeeding, and people under the age of 18.
Intermittent fasting is becoming more and more popular. And the chances that you have thought about practising intermittent fasting are particularly great if you’re already following a ketogenic diet.
The ketogenic diet and intermittent fasting work synergistically. For this reason, many people combine the two practices.
Before going into detail about how the two diets complement each other, let’s have a closer look at different intermittent fasting protocols.
6 intermittent fasting protocols
With intermittent fasting, you fast for a certain time every day. Protocols differ in fasting duration.
If you’re new to intermittent fasting and its health benefits, we recommend our introductory article on intermittent fasting.
14/10-fasting
14/10-fasting is a very beginner-friendly intermittent fasting protocol. You fast daily for 14 hours and eat within a 10-hour window. Fourteen hours may sound like a long time, but remember that you’ll be asleep for a good chunk of that time.
So you could, for instance, have breakfast at 8 am, have lunch around noon, and finish dinner by 6 pm. This is just one example; the exact timing is flexible.
16/8-fasting
16/8-fasting is the most popular intermittent fasting protocol and is also beginner-friendly. Most people following this protocol skip either breakfast or dinner. So you may eat from 8 am to 4 pm or from noon to 8 pm. You can also have three main meals within this time; you just have to move them a bit closer together.
18/6-fasting
18/6 fasting is a bit more advanced than 16/8 fasting, is it requires an additional two hours of fasting.
Most people practising the 18/6 method skip breakfast or dinner and eat just two meals per day.
OMAD or 24-hours fasting
One-Meal-A-Day (OMAD) is a very advanced intermittent fasting protocol. As its name suggests, you eat only one meal per day. Assuming that this meal doesn’t take much time to eat, you fast for almost 24 hours. For this reason, this protocol is also known as 24-hours fasting.
However, many people following OMAD still eat several courses and do take more time (up to 3-4 hours) to eat.
ADF
Alternate-Day-Fasting (ADF) is another advanced intermittent fasting protocol, and you should not try it without prior intermittent fasting experience. On this protocol, you eat only every other day, fasting for about 36 hours in between.
So, you could finish dinner by 8 pm and break your fast with a breakfast at 8 am two mornings later.
Because going without food for an entire day can be very challenging, some people also follow a modified version, which includes eating 500 – 600 kcal on the fasting day.
5/2-fasting
5/2-fasting is similar to ADF, but you only fast two days per week. These two days are usually non-consecutive.
There is also a modified version which includes eating 500 – 600 kcal per day.
You don’t have to strictly follow one particular method, and you can also combine different approaches. You can, for instance, do a 24-hour fast one or twice per week and practise 16/8-fasting on the remaining days.
Why can it be beneficial to combine the ketogenic diet with intermittent fasting?
Most people who start a ketogenic diet soon notice that their appetite decreases. The next meal simply loses its importance, and it becomes easy to skip a meal. So, when on a ketogenic diet, you almost automatically slip into intermittent fasting. Consciously practising intermittent fasting by keeping an eye on the clock is just a small step further.
But there are more good reasons to complement a ketogenic diet with intermittent fasting. These two diets work better together, as they create positive feedback loops. When it comes to weight loss, adding intermittent fasting to a keto diet can help overcome a weight loss plateau.
They reduce insulin levels
Carbs and sugars raise blood sugar levels. The pancreas then secretes insulin, which helps to bring the blood sugar back to normal. Because the ketogenic diet is low in carbs, it helps to keep insulin levels low.
But insulin still rises whenever you eat something. This is because not only carbs and sugar stimulate insulin secretion –protein does too. The safest way to keep your insulin low is, therefore, not to eat at all.
Then again, we all have to eat to survive. But we don’t have to eat constantly. Instead, we can take breaks from eating and make up the calory deficit by eating more at a given meal. That’s what intermittent fasting is about.
So, while the ketogenic diet minimizes insulin release when you eat, with intermittent fasting, your insulin levels only go up once, twice, or maybe three times per day (depending on the method you follow).
This is why the ketogenic diet and intermittent fasting are such a powerful combination in battling insulin resistance.
While it’s clear how the two diets mechanistically work together, there are hardly any trials studying the synergetic effects. Nevertheless, one small study by Furmli et al with three diabetes type 2 patients demonstrates how powerful the combination is. The participants fasted for 24 hours three times a week while following a low-carb diet.
After a few months, all three patients significantly decreased their HbA1c (reflecting the average blood sugar levels for the last two to three months), despite coming off insulin. And it almost goes without saying that they also lost significant amounts of weight and waist circumference.
Disclaimer: Intermittent fasting is a very powerful method to reduce insulin resistance and improve diabetes type 2. But for these reasons, it can also be dangerous. Diabetic patients who practice intermittent fasting are at risk of experiencing life-threatening hypoglycemia. These patients should only fast under close medical supervision while regularly checking their blood sugar levels.
Intermittent fasting deepens ketosis
High insulin levels inhibit ketosis, which is the reason why a ketogenic diet stimulates ketosis. But insulin levels are lowest when you’re not eating at all. For this reason, fasting is the most effective way to reach ketosis.
Ketones are produced from fat, but the fat doesn’t necessarily have to come from food; it can also come from stored body fat. In fact, when you want to lose body fat, it should primarily come from stored body fat. And while not eating, you should give your body the time and opportunity to access body fat and turn it into ketones.
When following a ketogenic diet, intermittent fasting is a great way to deepen ketosis. You may even be able to increase your carb intake a bit and still experience the benefits of ketosis and the ketogenic diet. Eating may then interrupt ketosis for a short time, but fasting will allow you to quickly re-enter ketosis.
Intermittent fasting helps to maintain muscles when losing weight
Autophagy is a recycling process that is responsible for many health benefits of intermittent fasting.
When you regularly eat without longer eating breaks, your cells are constantly supplied with fresh nutrients. Once you start fasting, your cells are forced to break down old molecules and use the resulting building blocks to produce new molecules. This process is vital for cellular health, as it allows cells to get rid of old debris, which inhibits cellular processes. Through autophagy, everything runs more smoothly again.
The rate of autophagy declines with aging, and not surprisingly, problems with autophagy are seen in many chronic conditions, such as diabetes. Autophagy is also thought to be responsible for the anti-aging effects of intermittent fasting. For this reason, autophagy is also known as the fountain of youth.
A ketogenic diet can also stimulate autophagy. So there is again a synergetic effect between the two.
With regards to the ketogenic diet and weight loss, autophagy provides more benefits. Of course, when we talk about weight loss, we mean fat loss. But on most diets, we also lose valuable muscles.
Autophagy can serve as a tool to preserve muscle mass. As autophagy involves the recycling of proteins, it reduces the need to break-down protein from muscles.
How to get started
Together, intermittent fasting and the ketogenic diet are a powerful combination. But we don’t recommend starting both at the same time. Start with a ketogenic diet. Once you get used to it and you’re keto-adapted, you’ll notice that your appetite decreases. Then it’s a good time to start with intermittent fasting.
Start off with a beginner-friendly protocol such as the 14/10 method. Depending on your goals, you can then increase the fasting time to 16 or 18 hours daily or even fast for entire days. For example, when you are not insulin resistant and don’t have much weight to lose, fasting for 14 or 16 hours daily may be sufficient for you.