Fact Checked by

Sofia Norton, RD

Should You Do Intermittent Fasting While on Keto?

What do you get when you combine a keto diet with intermittent fasting? Here are the benefits and risks of taking this approach.
Keto fasting


Intermittent fasting is growing in popularity, and some choose to do it in conjunction with a keto diet. In theory, fasting should work to get you into ketosis more quickly.

If you are on the keto diet, you might be thinking, “Jeez, this is already hard enough.”

I mean, the keto diet is generally restrictive, since you’re slashing carbs and bulking up on fats, and there’s a lot of precision and counting that goes into keeping track of macronutrients and staying in ketosis.

Throw intermittent fasting into the mix and you get “keto fasting“. A new way to practice keto by combining intermittent fasting (or IF) with the ketogenic diet.

While it’s growing in popularity, the true benefits of keto fasting are still questionable and the challenge of combing the two may not be worth it. Not only do you have to monitor everything you’re eating, your macronutrient requirements, and your ketosis levels throughout the day but now you’re also balancing the timing of it all.

Yet there has been great buzz about the benefits of doing intermittent fasting in terms of promoting weight loss, having greater energy and sleep, and stabilizing blood sugar.

Why is keto fasting becoming popular?

“Fasting leads to drops in blood sugar levels and can deplete liver glycogen stores quickly,” says Sofia Norton, RD at Kiss My Keto, which makes sense that it would be helpful for those on keto, too.

intermittent fasting embodied in a plate of food made to look like a clock

Does intermittent fasting help with keto?

A 2002 study involving children put on a keto diet found no differences in the time it took to get into ketosis between protocols that used a fast and those that did not.

What that means is that you probably won’t get into ketosis sooner just because you fasted.

So, unless you want to do intermittent fasting when on keto and find it to be helpful for your progress, don’t feel obligated to do it just because of the potential benefits, which have not been thoroughly studied.

How might keto and intermittent fasting work together?

Intermittent fasting should, in theory, speed up the time it takes to get into ketosis.

You could do both together, since going on an intermittent fasting program could help you get into ketosis faster and stay there, due to the benefits on blood sugar levels.

Yet, there is not enough evidence to show that fasting can lead to such effects.

Side-effects of combining intermittent fasting and the keto diet. 

  • Intermittent fasting can cause sharper drops in blood glucose and glycogen depletion than gradual initiation of a keto diet. This can leave you feeling weak, tired, and hangry.
  • And it’s scarier for those with medical conditions involving blood sugar and metabolism.
  • For those with diabetes, the challenge can be even greater because it is difficult to balance your insulin needs when you completely skip meals. It can even be downright dangerous.

Of course, if you do have diabetes or a medical condition, consult with your doctor before starting IF when on keto. (And you should also get the green light for doing keto in general, too!)

Should you combine intermittent fasting and keto?

  • Intermittent fasting can definitely enhance the weight-loss and longevity benefits of the keto diet!
  • However, if you’re not ready to commit to a combo of both carb and food intake restriction, it may be too much for you.
  • Again, it’s double the restriction and attentiveness to both diets.

The best diet is one you can commit to in the long run, and IF combined with keto can be too extreme for most people.

How to make keto fasting easier. 

Fast in shorter increments!

By going for shorter fasts (say, 10 hours) instead of loner ones, you can make it easier to transition into and get used to.

Fasting only periodically and when you’re not busy can also make the task less daunting. So, you may not want to do it every day, every week, and during times when you’re super crazed at work or are juggling a million tasks in the day!

You could, for example, fast every other weekend. The 5:2 diet, where you eat regularly for 5 days and eat few calories for 2 can also seem more sustainable than complete food restriction.

Intermittent Fasting Schedule 

OK—let’s plan!

If you’re set on trying keto fast, here’s what an intermittent fasting schedule might look like when you’re getting started.

16:8 Fasting Method

The best and most effective fasting method is the 16:8 fast.

  • 8 PM: Eat dinner (Start your fast)
  • Morning: Skip breakfast
  • 12 PM: Eat lunch (Break your fast)

This basically means you’ll fast for 16 hours. Most people choose an overnight fast because it still counts as a fast and is easier to do than whole-day fasting.

To make things easier, you could utilize a pre-made keto delivery service to save time on cooking and meal prep. The Fresh n’ Lean Keto Plan is fully keto-approved, and the meal plan changes each week so you’ll get a variety of nutrients in your diet. 

Eat fat-rich foods and MCTs.

  • During the feeding window of the 16:8 fast, eat fat-rich foods to support your ketosis:
    • Butter
    • Olive oil
    • Turkey bacon
    • Avocado
  • And you can add in MCTs to help make ketones and boost keto results. Incorporating MCT oil can also help speed up the process since the liver converts MCTs into ketones.
  • Other sources of MCTs include coconut and palm kernel oil, too, so feel free to use those in coffee, baked goods and recipes, and more.

So, intrigued? Give it a go and see if it works for you!

Keto Fasting FAQs

How long should you fast on keto?

1-2 times per week.

Like with all things in life, practice moderation. Fasting once or twice a week should be enough to give you the weight-loss and health benefits of IF. Avoid whole-day fasts or practice them every other week at most. You need some food each day to avoid being malnourished and low in fuel.

What’s the fastest way to get into ketosis?

Research shows that people get into ketosis within 3-7 days on average. Getting into ketosis sooner than that is not physiologically possible. 

Your body needs to use up its glycogen stores and send signals that promote the release of triglycerides from fat to be converted into ketones, all of which takes a set amount of time. Any differences in the time it takes to get into ketosis between people are small, so it’s okay to think in general terms for timing.

Can you feel when you are in ketosis?

Most people can tell they’re in ketosis by looking at the signs and symptoms.

These signs might be:

  • Greater ketone levels in the blood and urine
  • Fruity breath (which comes from the presence of acetone, which is a ketone body)
  • Weight loss (caused by initial water loss)
  • Mental clarity (which you’ll find after a short period of brain fog from low glycogen stores as the body adjusts)
  • Sleep changes (ketones can affect how your brain works, so it can be irregular at first, but then you should sleep better).

The best way to check if you are in ketosis is by testing your ketone levels with urine test strips. These are non-invasive, cheap, and can be bought at the pharmacy.

Another way is with a blood ketone meter, but this one is more expensive and invasive. 

How much weight can you lose in a month with intermittent fasting?

You can lose 1-2 pounds a week.

Yes, that’s huge! Yet this happens if you eat fewer calories than your body is burning. Initially, you may notice even greater weight loss, but this is mostly water weight.

Can you lose belly fat with intermittent fasting?

Yes, definitely.

If you are doing IF and keto together, you might lose weight faster though—especially in the abdominal region!

The keto diet combined with IF can improve metabolic health, which can boost visceral fat (belly fat) loss.

Can you drink water when intermittent fasting?

Yes, you should drink water while doing IF.

Not drinking water while fasting can put you at risk of becoming dehydrated and it can also negatively affect your metabolic functioning.

Can you have keto coffee while fasting?

You can have sugar-free, dark coffee since it contains zero calories, too. (Great for java lovers!)

Plus, a more popular drink is bulletproof coffee, which is made with freshly brewed coffee, butter or ghee, and MCT oil. The added fats in this coffee won’t spike blood glucose but can actually support ketone production—which speeds up the time to ketosis.

What can you have while fasting?

Some forms of IF, like the 5:2 diet, involve a small amount of food during the fasting period, which is typically around 500 calories worth of food a day.

Others, like the 16:8 method, allow only zero-calorie liquids like water, tea, and coffee during the fasting window.

If you’re combining intermittent fasting with the keto diet, however, you can safely consume MCT oil, other oils, and butter during your fasting window. These are pure sources of fat, and fat does not raise blood glucose levels—the main point of IF. 

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