Intermittent Fasting 20/4: The Complete Guide

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In recent years, intermittent fasting has become a very popular approach to dieting.

Unlike most other weight loss diets, which usually are defined by what you can and cannot eat, intermittent fasting diets are defined by when you can and cannot eat.

Although there are quite a few iterations of intermittent fasting, 20/4 intermittent fasting is one of the more popular approaches to time-restricted eating intermittent fasting.

But, what is 20/4 intermittent fasting? Is intermittent fasting 20/4 good for weight loss and health?

In this guide, we will discuss how to do 20/4 intermittent fasting, the pros and cons of intermittent fasting 20/4, and tips for those who want to try intermittent fasting 20/4.

We will cover: 

  • What Is Intermittent Fasting 20/4?
  • How to Do 20/40 Intermittent Fasting
  • What to Eat With Intermittent Fasting 20/4
  • Does 20:4 Intermittent Fasting Lead to Weight Loss?
  • Benefits of Intermittent Fasting 20/4
  • Potential Downsides of 20:4 Intermittent Fasting
  • Tips for Intermittent Fasting 20/4

Let’s jump in!

takeaway food that looks healthy

What Is Intermittent Fasting 20/4?

Also known as 20/4 intermittent fasting, 20/4 intermittent fasting is an advanced form of a time-restricted eating type of intermittent fasting.

The 20/4 intermittent fasting diet involves splitting the day into a 20-hour fast and a 4-hour eating window.

How to Do 20/40 Intermittent Fasting

Any way you look at it, intermittent fasting 20/4 can be pretty challenging, especially if you’re new to intermittent fasting diets and time-restricted eating.

A 20-hour fast is a long time, and can be tricky unless you plan your food choices well.

The good thing is that as with any intermittent fasting diet, with 20/4 intermittent fasting, dieters can choose how they schedule their fasting hours and eating window.

With that said, most people complete the 20-hour fast by delaying the first meal of the day as long as possible, extending the overnight fast well into the day.

For example, someone might finish their last meal of the day by 6:00 PM, and then fasting overnight and all the way until 2:00 PM the next day.

Then, they would break the 20-hour fast by eating their first meal at 2:00 PM.

Other people might choose to delay the first meal even longer, fasting until 4:00 or 5:00 PM, and then finishing their last meal by 8:00 or 9:00 PM, respectively.

Depending on your personal schedule and preferences, you might also do intermittent fasting 20/4 by eating earlier in the day and beginning the 20 hour fast in the afternoon.

For instance, some people who wake up early find it easier to have their first meal at noon and then stop eating anything by 4:00 PM though until noon the next day.

Moreover, although most people feel best and find it easiest to keep the same eating and fasting schedule every day, with intermittent fasting diets like 20/4 intermittent fasting, you have the freedom to schedule your fasting and eating windows however you want to from day to day.

You might choose to start your eating window later on weekend days and break the 20-hour fast earlier during the work week.

Essentially, there are no specific rules as to how you have to schedule your eating and fasting windows, as long as you fast for 20 hours in a row.

3 plates of food - a salad, bread, and a calzone

What to Eat With Intermittent Fasting 20/4

Moreover, with intermittent fasting 20:4, what you eat is entirely up to you, as long as you are consuming it during your eating window.

With that said, to maximize your weight loss efforts and support optimal health, the quality of the food you eat matters just as much—if not more—than the quantity.

Focus on whole, natural, unprocessed foods like vegetables, fruits, whole grains, lean proteins, legumes, seeds, nuts, low-fat dairy, and healthy fats.

Avoid processed foods like canned soups, frozen dinners, packaged cakes and cookies, sugary cereals, refined grains, sweetened beverages, chips and fried foods, and anything with excessive sugar, salt, trans fats, artificial sweeteners, or alcohol.

During the 20-hour fasting window, you shouldn’t be eating anything caloric, if you’re trying to be strict in your intermittent fasting diet.

Non-caloric drinks such as water, seltzer, and herbal tea are permitted as long as you aren’t adding sweeteners.

You can also drink black coffee while intermittent fasting.

One cup (240 ml) of black coffee only contains approximately 3 calories and just trace amounts of protein, fat, and minerals.

Therefore, 1-2 cups of black coffee won’t really induce any metabolic changes or take you out of a faster state.

However, adding caloric sweeteners or cream, MCT oil, milk, or grass-fed butter will break your fast.

a notebook that says intermittent fasting, a plate and fork and knife

Does 20:4 Intermittent Fasting Lead to Weight Loss?

Like most diets, many people turn to intermittent fasting 20/4 as a way to lose weight, and evidence suggests that intermittent fasting diets can cause significant reductions in weight. 

For example, evidence suggests that disruptions in healthy circadian rhythms—such as those induced by shift work or late-night eating—cause unfavorable changes in gut microbiome, which in turn, negatively impact metabolism. 

Additionally, and perhaps most significantly, 20/4 intermittent fasting can lead to weight loss due to behavioral changes like taking in fewer calories simply because your open time to eat is so restricted.

In addition to likely reducing your caloric intake significantly by severely limiting the permissible amount of time you can eat—there’s also a mindfulness aspect to intermittent fasting 20/4 that can indirectly increase weight loss.

When you have such a restricted eating window to work with, you have to be more deliberate with your food choices in terms of what and when you’re putting food in your mouth.

This can help eliminate mindless eating and encourage you to make smarter, healthier, more filling food choices.

a plate with a heart on it

Benefits Of Intermittent Fasting 20/4

There are a variety of reported benefits of intermittent fasting diets such as 20/4 intermittent fasting, such as supporting weight loss, promoting autophagy, and reducing oxidative stress and inflammation.

There is also the psychological or behavioral benefit of intermittent fasting as a weight loss approach.

Many dieters find intermittent fasting to be a more appealing dietary approach than diets that restrict which foods you can eat

Even with the extremely time-limited 20/4 intermittent fasting diet with its 20-hour fast, you still have complete freedom over your food choices, with no limitations on any types of foods or food groups as long as you are consuming them during your eating window.

When no foods are “off-limits,” dieters often experience less of an intense craving or longing for them. 

For this reason, one of the benefits of intermittent fasting 20/4 is that the freedom of choice can be great for those who tend to miss what they “can’t” have, and can help make the diet more sustainable in the long term.

Additionally, the flexibility in terms of how you schedule your 20 hour fast makes this weight loss diet feel empowering; you are in the driver’s seat.

a healthy food bircher bowl

Potential Downsides Of 20:4 Intermittent Fasting 

Although intermittent fasting 20/4 can potentially help you lose weight and improve your health, there are also possible drawbacks, particularly due to the prolonged 20-hour fast.

Some people experience ravenous hunger, headaches, dizziness, difficulty concentrating, low energy, irritability, poor cognitive performance, impaired exercise performance, irritability, and mood swings.

Intermittent fasting 20:4 can also interfere with sleeping well if you go to bed hungry. This often happens if you begin your eating window early in the day so that it’s already been many hours since you’ve eaten by the time you go to bed.

Intermittent fasting 20/4 is also not usually a good diet for those trying to improve athletic performance or do intense exercise training because it can compromise your fueling and recovery.

a person looking healthy after intermittent fasting 20/4

Another downside of 20/4 intermittent fasting is its potential to interfere with your social life.

Having such a limited window to eat can make it difficult to participate in social eating engagements.

Although you do have the latitude to choose when you do your eating, it can be hard to be around people who are eating when you aren’t or to take part in family meals or celebratory dinners if they don’t align well with your diet schedule.

Finally, some people find that the prolonged restriction of a 20-hour fast triggers compensatory binging once their eating window opens up.

These people can find it difficult to make rational food choices and consume sensible portions because their blood sugar levels have been so low and they’re anticipating the next 20-hour fast.

a nice breakfast bowl for intermittent fasters and a measuring tape

Tips for Intermittent Fasting 20/4

Following intermittent fasting 20/4 can be hard, especially at first, because fasting for 20 hours is challenging. 

Here are some tips for making intermittent fasting easier:

  • Plan your meals ahead of time.
  • Consume filling, nutritious, minimally-processed whole foods such as high-quality lean proteins, vegetables, eggs, fruit, seeds, legumes, and healthy fats like avocados and nuts.
  • Exercise during your eating window to ensure you’re fueled for the workout and can refuel afterwards.
  • Build up to 20:4 intermittent fasting by starting with 16:8 intermittent fasting and then progressing to 18:6 intermittent fasting.

Most importantly, listen to your body. 

Your diet should help you feel your best. If a 20-hour fast isn’t working for you, adjust down to something less restrictive.

For other diet ideas, check out our popular diets for runners guide.

a clock and portions of chick pea curry
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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