Intermittent Fasting 18/6: The Complete Guide

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There is a near-endless smorgasbord of popular diets these days, and the list seems to be ever-expanding. There’s the Mediterranean diet, the keto diet, vegan or plant-based diets, the paleo, and the DASH diet, to name just a few.

Although the specific characteristics that define and differentiate each one of these popular diets vary, what they share is that most fad diets are defined by what you can or cannot eat.

Intermittent fasting is another approach to eating and can be considered a popular diet, but rather than being defined by what you can and cannot eat, intermittent fasting is defined by when you can and cannot eat.

The intermittent fasting 18/6 approach is one of the most common ways that people practice intermittent fasting. It’s a specific iteration of intermittent fasting that involves an 18-hour fast and a short, 6-hour eating window.

In this guide, we will discuss the pros and cons of the 18/6 intermittent fasting diet and how to follow the intermittent fasting 18/6 diet.

We will discuss: 

  • What Is Intermittent Fasting 18/6?
  • How to Do 18:6 Intermittent Fasting 
  • What Can You Eat With Intermittent Fasting 18/6?
  • Benefits of 18/6 Intermittent Fasting
  • Potential Drawbacks of Intermittent Fasting 18/6
  • Tips for 18 6 Intermittent Fasting

Let’s get started!

A notebook that says intermittent fasting, a clock and utensils.

What Is Intermittent Fasting 18/6?

Intermittent fasting 18/6, also sometimes referred to as 18/6 intermittent fasting or written as intermittent fasting 18:6, is a specific pattern of intermittent fasting.

Intermittent fasting is an umbrella term that refers to a dietary approach that involves limiting the time period in which you eat during the day and deliberately extending the period of restricted eating or fasting. 

Proponents of intermittent fasting believe it can be an effective avenue for weight loss and for improving other markers of health.

Most intermittent fasting diets involve specific patterns of times eating intervals interspersed with timed fasting intervals. This is referred to as time-restricted eating (TRE) or time-restricted feeding (TRF).

With time-restricted eating, there is a reduced “eating window” and an extended fasting window.

A bowl of food, a clock and a measuring tape.

Time-restricted intermittent fasting diets are often referred to with specific numbers that correspond to the number of hours in a 24-hour day that you are maintaining a fast and the number of hours in a 24-hour day that is open for your eating window.

You must consume all of your calories for the day within the eating window.

Intermittent fasting 18:6 is a perfect example of this type of intermittent fasting.

The “18” refers to an 18 hour fast, and the 6 denotes a 6 hour eating window.

You will see any number of combinations, such as intermittent fasting 20:4 and intermittent fasting 14:10.

The larger the first number, the longer the period of fasting.

One of the most common methods of intermittent fasting is 16:8, which might be carried out by having the first meal at 11 am and finishing the last meal or snack at 7 pm.

In addition to time-restricted eating, intermittent fasting can involve fasting for an entire day, one or more days per week, followed by days of open and free eating.

This type of approach to intermittent fasting is sometimes called alternate day fasting (ADF), especially if you flip-flop between 24-hour fasting and eating at liberty every other day.

However, more often, people taking this approach to intermittent fasting may have one or two days a week where they don’t eat anything for at least 24 hours, but all of the other days would be normal eating.

An empty plate with utensils and a clock on it.

How to Do 18:6 Intermittent Fasting 

As mentioned, intermittent fasting 18/6 is one of the time-restricted eating methods of intermittent fasting.

It involves splitting up each 24-hour day into an 18-hour continuous fast and a 6-hour open window where you can eat.

You can schedule these hours any way you see fit.

Most people practice intermittent fasting by extending the overnight fast as long as possible such that they don’t have their first meal or snack of the day until at least mid-day or early afternoon.

Then, you are free to eat or drink your calories until a certain time in the evening, or potentially right up until bedtime, depending on the number of hours for your fast, your preferences, and when you break your fast.

With 18:6 intermittent fasting, you might wait until noon to have your first meal of the day and then finish your last meal by 6 PM.

The 18/6 intermittent fasting pattern is more aggressive than the more common 16/8 pattern in that your eating window is quite restrictive.

Therefore, although many people who do intermittent fasting start their eating widow at 12 PM, you might want to wait until 1 PM, or even 2 PM, with 18:6 intermittent fasting.

There are no time-bound rules, so you should consider what eating schedule works best for you based on the time of day that you wake up and go to bed.

A plate of food, an empty plate, and a mini clock.

What Can You Eat With Intermittent Fasting 18/6?

Technically, you can eat anything during your eating window when you are following a time-restricted feeding intermittent fasting diet.

However, depending on your health, weight loss, and body composition goals, what you eat during your eating window can be just as important as the fact that you’re restricting your caloric intake to a set number of hours.

In other words, even if you fast for 18 hours or more if you go hog wild and binge on a lot of processed foods and empty calories once your eating window opens, you are not going to achieve the weight loss and health benefits you are seeking.

Making smart food choices will also ensure that you are satiated during an extended fast. 

Foods that provide sustained energy rather than a quick crash will help keep your blood sugar levels stable while you’re unable to ingest calories.

For example, nutrient-dense complex carbohydrates with lots of fiber—such as beans, lentils, quinoa, and sweet potatoes—will keep you fuller for longer compared to sugary breakfast cereal, bagels, and white pasta.

Healthy fats and lean proteins take longer to digest and will keep you satisfied for much longer while simultaneously providing essential nutrients for your body.

A cup of black coffee with coffee beans on the saucer.

Because most people structure their intermittent fasting diet schedule by delaying the first meal of the day as long as possible, the common question becomes, “Can you drink coffee while intermittent fasting?”

Unless you’re interested in following the most extreme version of intermittent fasting for mental or behavioral health reasons, you can drink black coffee without any sugar, milk, or cream during the fasting period.

One cup (240 ml) of black coffee only contains approximately 3 calories, with just trace amounts of protein, fat, and minerals, so even a cup or two of coffee won’t really induce any metabolic changes or take you out of a fasted state.

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

Some people do allow clean fats in their coffee while intermittent fasting (as with Bulletproof coffee) because the fat will not alter your blood sugar significantly.

However, adding fat to your coffee will affect your metabolism so it will take you out of the fasted state in the strict sense.

In addition to black coffee, herbal tea, seltzer, and other non-caloric beverages are allowed during your fast because they do not really affect your metabolism.

Water, of course, is encouraged, and staying well hydrated is one of the most effective and healthy ways to support your metabolism and make it through the fasted period. 

A person holding a glass of water,

Benefits of 18/6 Intermittent Fasting

So, why do people practice intermittent fasting? 

There are a variety of reported benefits of intermittent fasting. Like most diets, many people turn to intermittent fasting as a way to lose weight.

By limiting the number of hours you can eat in a day, there’s simply less time to eat and potentially gorge on excessive food.

This directly reduces your daily caloric intake.

There’s also a mindfulness aspect of intermittent fasting that can indirectly increase weight loss.

If you have a restricted eating window, you have to be more mindful of your food choices and what and when you’re putting food in your mouth, which can cut back on mindless eating and encourage you to make smarter (and thus, healthier) food choices.

Additional benefits of 18:6 intermittent fasting diet include the following:

  • Reducing visceral or abdominal fat
  • Improving cellular health
  • Providing more freedom of food choices over other popular diets
People running on a treadmill.

Potential Downsides Of 18:6 Intermittent Fasting 

There are also potential drawbacks of the prolonged 18-hour fast with 18:6 intermittent fasting.

Some people report feelings of hunger, headaches, dizziness, difficulty concentrating, low energy, and moodiness.

Intermittent fasting 18/6 can also interfere with good sleep if you go to bed hungry because you started your eating time early in the day.

Depending on how you time your workouts relative to your eating and fasting windows, intermittent fasting can also decrease athletic performance.

Endurance activities and high-intensity workouts can be very difficult (and potentially unsafe) to perform in the fasted state.

Furthermore, if you wait until after your eating window has ended for the day to exercise, your recovery can be compromised because you will not be able to refuel after working out.

Finally, some people find that they are triggered to binge eat once their eating window opens up.

A plate of food.

Tips for 18 6 Intermittent Fasting

Following intermittent fasting 18/6 can be challenging, especially at first. An 18-hour fast is quite long. However, here are some tips for making intermittent fasting easier:

  • Drink plenty of water, particularly during the 18 hour fast, and add electrolytes to prevent dizziness and promote hydration.
  • Try to avoid overeating when your eating window opens by planning your meals ahead of time.
  • Be mindful and present when you eat, paying particular attention to your diet quality. Focus on minimally-processed whole foods such as high-quality lean proteins, vegetables, eggs, fruit, seeds, legumes, and healthy fats like avocados and nuts.
  • Eat more fiber, healthy fat, and protein to promote satiety and limit processed foods.
  • Don’t exercise in the fasted state; wait until you’ve broken the fast.
  • Go to bed earlier to prevent late-night hunger and cravings.
  • Build up to 18:6 intermittent fasting by starting with 14:10 intermittent fasting and then progressing to 16:8 intermittent fasting.

Remember to listen to your body. If you’re feeling lethargic or starving on the 18:6 intermittent fasting pattern, feel free to adjust the length of your fast.

If you prefer to try a 24-hour fast once a week, check out the benefits in our guide.

A paper bag of food with the groceries spilling out.
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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