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By now, you’ve probably heard about the many benefits of intermittent fasting. Many people swear by intermittent fasting and its many health benefits, including helping them lose weight, manage their blood sugar control, balance insulin levels, and prevent chronic illnesses[*][*][*].

The practice of intermittent fasting may sound counterintuitive to you. For the longest time, conventional nutrition told you to eat more frequent small meals. The idea was that snacking and more frequent meals would cause your metabolism to work harder and continuously, thereby burning more calories — but new studies say otherwise. 

There are many approaches to intermittent fasting, with fasts ranging from several hours to a couple of days. Below, you’ll learn about the different types of intermittent fasting, how frequently you should fast, and why one of the most common types of fasting — known as the intermittent fasting 16/8 method — might be right for you.

Types of Intermittent Fasting

Intermittent fasting means eating within a certain window of time and then abstaining from food the rest of the time. The most common type of intermittent fasting is:

Fasting Within a Certain Window

When most people mention intermittent fasting, this is usually what they mean.

An eating window can range anywhere from one to eight hours, with the most common eating window is eight hours. This means a typical day would consist of 16 hours of fasting and eight hours of eating. This is often referred to as intermittent fasting 16/8. For example, you might only eat between:

  • 10am and 6pm
  • 11am and 7pm
  • 12pm and 8pm

Outside of those hours, no calories will be consumed. You can drink water and black coffee, but you won’t eat any real food or drink any caloric beverages. 

Some people will decrease the eating window even further, such as 20/4 or even as low as 23/1, only eating for one hour a day. Starting with the standard intermittent fasting 16/8 is best for most people.

Intermittent Fasting 16/8

If you’re just beginning to experiment with intermittent fasting, a common approach is to eat within an eight-hour window, then undergoing a fasting period lasting 16 hours. Most people follow this practice every day, eating their first meal mid-morning or over the noon hour, then eating their last meal at dinnertime. 

The 16/8 fasting diet is mentally and physically more manageable than other approaches, simply because it doesn’t require that much change from your regular routine.

When partaking in this form of intermittent fasting, you will skip one meal (most likely breakfast) in the morning. You will eat a late breakfast, lunch, and finally dinner within an eight-hour time frame, then fast until breakfast the next day. 

Other Types of Intermittent Fasting

Other types of intermittent fasting include:

  1. Skipping meals each day, such as not having breakfast or lunch and eating a nutritious meal at dinner, then fasting until breakfast the next morning.
  2. Choosing a couple of days to fast each week, such as fasting for 24 hours on Monday and Wednesday.
  3. Alternate day fasting, where you alternate between eating and fasting days. For example, you would eat regularly on Monday, fast on Tuesday, then eat again on Wednesday.
  4. Fat fasting, which means eating only fats for a few days to induce ketosis. This is common with those following the ketogenic diet. Although you’re still eating food during this time, it can be considered an intermittent form of fasting because you’re “fasting” your body of glucose through the very high fat intake.

Now that you understand the amount of time involved with common forms of intermittent fasting, it’s time to talk about frequency. How often can you partake in these forms of fasting?

Fasting Frequency

There is no right or wrong approach to an intermittent fasting schedule — there is only a schedule that works best for you. Keep a close watch on your energy levels, mood, and weight loss progress, noting how various methods affect you physically and mentally. 

To get the most benefit, most people practice intermittent fasting on a weekly or bi-weekly basis. Below are a few fasting schedules that might work for you. 

What Does Daily Intermittent Fasting Do?

Daily Fasts 

Those who practice daily intermittent fasting will typically have a shorter fasting window and a longer eating window. For example, if you follow the intermittent fasting 16/8 method, you could skip breakfast daily, making lunch your first meal of the day. 

Weekly Fasts

If you choose a fasting window lasting 24 hours or longer, it’s recommended to only practice intermittent fasting 1–2 times per week. Fasting more frequently than that could cause muscle loss or other adverse effects. 

Bi-Weekly Fasts

If your fast lasts 36 or 48 hours, you’re best taking a full week or two weeks off between fasts. Start with a more moderate approach, taking two full weeks off between fasts. Once your body becomes more accustomed to the practice, you can aim for a more aggressive approach, taking only a single week off in between.

How to Start Intermittent Fasting 

Here’s the bottom line when it comes to intermittent fasting: There’s really no wrong answer here. Just pay attention to how your body responds to what you’re doing, and consult a dietitian or doctor with any concerns over potential negative side effects. You might want to:

  • Test your glucose and ketone levels and monitor your glucose-ketone index for changes.
  • Consider your carb intake. Eating lower carb helps reduce any hunger pangs when starting intermittent fasting.
  • Start with the 16/8 window first and make changes from there based on what works for your lifestyle and schedule.

Adjust what you’re doing as needed. Also, keep in mind that life changes can happen, so you might find it’s better to tweak your eating window over time or be a little more lenient at certain periods.

Give yourself time to adjust to the schedule of intermittent fasting too. Some people adjust easily within a few days, while others need a couple of weeks to get used to it.

A Note on Calories and Nutrition

When practicing intermittent fasting, it’s imperative you get enough nutrients — the right nutrients, that is — during your eating window.

Intermittent Fasting 16/8: Eating Too Few Calories for an Extended Period of Time

Be sure to stick to your low-carb, keto meal plan, eating plenty of healthy fats, plus dark, leafy greens and plenty of protein. Simply because you have skipped a meal or gone a full 24 hours without eating, do not use it as an excuse to pack in the sugars, starch, junk food, or other foods low in nutrients. 

Focus on real whole foods so you get the most nutrients outside your fasting window. This allows you the benefits of fasting while still consuming optimal nutrition. 

The key here is to make the benefits of intermittent fasting work for you over the long-term, for your work patterns and lifestyle.

Make Intermittent Fasting Work for You

No one way of fasting is perfect for everyone, but just about any healthy person can benefit from intermittent fasting.

Intermittent fasting is generally safe to do as often as you’d like. Just make sure you’re eating enough nutritious, whole foods in between.

Combining the ketogenic diet with intermittent fasting is a great way to lose weight without counting calories.

And lastly, don’t be afraid to experiment and find what works best for you. While the intermittent fasting 16/8 approach might work for most, there’s no one-size-fits-all fasting method. 

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Responses (12)

  1. I was wondering how long an intermittent fast should be undertaken. I had been doing it for 6 months, eating 11:30 to 7:30 PM, when I got a flu virus and felt hungry in the mornings so I stopped.
    Wondering if at this point I could start again in a few months, or just do it once in a while for 2 weeks? Any thoughts on this? Thanks!

    1. Hi Nancy, there are different types of intermittent fasting. You can check out this article for the type of fasting that would suit you. Hope this can help!

  2. I started keto 2 weeks ago and I am already in ketosis (1.8mmol/L). My body fat 2 weeks ago was 31% and today it is 33% and my muscle mass decreased as well. Question: Does Keto decrease muscle that fast?

    1. Studies have also shown that the low-carb, high-fat ketogenic diet has muscle sparing effects. That means — once you’re fully fat-adapted— your body will prevent itself from breaking down muscle even as you’re burning through fat. You can check more details about muscle building while in keto here: https://perfectketo.com/keto-bodybuilding/

  3. I’m 75, went on intermittent fasting cold turkey 20 years ago. I feel great, my weight is down 45 pounds, I sleep better, feel better generally, and will never go back to the SAD way.

    If anyone is wanting to fast, grab a copy of Dr. Fung’s book, read it, then start fasting by eating one meal per day.

    Fasting promotes cellular housecleaning which the body does not get to do on 3 or 4 meals a day or all-day snacking.

    I feel better than at any other time in my life. Don’t be afraid! Just do it!

  4. I am just starting on Keto, I want to try the fasting, I have never done it before. Can you still drink the Base, Collagen, and MTC powder. Does the fasting only refer to solid foods?

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