【Done While You Sleep】The Benefits of 16-Hour Fasting and How to Do It Right, Plus Is Coffee OK? Why You’re Not Losing Weight, and Precautions

“My body just feels heavy for no clear reason…”

“I always get sleepy after meals.”

“I can never stick with a diet.”

A lot of people deal with worries like these, don’t they?

One approach that has been getting attention lately as an answer to these problems is 16-hour fasting.

16-hour fasting is a way of eating where you spend 16 hours of each day not eating.

There are no complicated food restrictions; you “just decide when you eat,” which makes it easy to try even if you’ve never done it before.

In this article, I’ll walk you through how 16-hour fasting works, the benefits you can expect, the right way to do it, and the precautions to keep in mind, all in plain terms.

Please read to the end and find the approach that works for you.

What Is 16-Hour Fasting? Understanding the Basics of How It Works

A Simple Rule: 16 Hours Without Eating, 8 Hours of Eating

16-hour fasting is a way of eating where, out of the 24 hours in a day, you set 16 hours as your “no-eating time” and 8 hours as your “eating window”.

It’s known as “intermittent fasting,” and in Japanese it’s also called “kanketsuteki danjiki,” which means the same thing.

You could say it’s an approach that focuses on “when you eat” rather than “what you eat.”

It’s also sometimes called “16:8,” and you can think of it as exactly the same thing.

It’s Surprisingly Easy Once You Count Your Sleep

The key point is that your 16-hour fasting period includes the time you spend sleeping.

For example, if you finish dinner at 8 p.m. and simply don’t eat until noon the next day, you’ve completed a 16-hour fast.

The time you actually spend awake and hungry is only about 8 to 10 hours, so it’s much easier to manage than you might expect.

You can do it just by skipping breakfast or eating dinner earlier, so there’s no need to overhaul your lifestyle.

Think of It as Setting “Closing Hours” for Your Body’s Shop

Every time food comes in, your body gets to work digesting and absorbing it.

If you eat three meals a day plus snacks and late-night bites, the “shop” that is your body ends up open 24 hours a day.

16-hour fasting is like giving this shop proper closing hours.

While the shop is closed, your body can get around to tidying up the store and sorting through the inventory stored in the warehouse (fat).

The idea behind this method is that by deliberately creating time when you don’t eat, you make it easier for your body’s natural regulating functions to do their job.

Why “16 Hours”?

There are many approaches when it comes to how long to go without food, such as 12 hours, 14 hours, or longer stretches like 18 hours.

Among them, 16 hours is popular probably because it strikes a good balance between expected benefits and how easy it is to keep up.

And rest assured: unlike a full-on fast where you go without food for days, this is a method where you still eat properly every day.

5 Health Benefits You Can Expect from 16-Hour Fasting

1. Autophagy Kicks In and Helps Rejuvenate Your Cells

About 16 hours after your last meal, a self-repair function in your cells called “autophagy” starts to kick in.

Autophagy is the process by which your cells break down and recycle old or damaged components inside them.

It’s easiest to think of it as a kind of deep clean for your cells.

Its importance became widely known around the world through the research of Professor Yoshinori Ohsumi, who won the 2016 Nobel Prize in Physiology or Medicine.

It’s said that a wide range of health benefits can be expected, including helping prevent aging, improving immune function, and lowering the risk of lifestyle-related diseases.

2. Your Body Becomes Better at Burning Fat

Think of it like a hybrid car that switches over to its electric motor when the gas runs low.

Because 16-hour fasting keeps you in fat-burning mode for longer, it tends to lead to a reduction in body fat.

Another plus for weight loss is that since your eating hours are limited, your total daily calorie intake naturally tends to go down.

That said, if you overeat during your 8-hour eating window, it defeats the purpose.

It’s important to focus on eating a balanced diet.

3. Your Gut Gets a Rest, and Your Digestion and Skin Improve

While you fast, your digestive organs get a break, which helps your gut recover and repair itself.

When your gut environment is in good shape, you can expect benefits like more regular bowel movements, clearer skin, and a stronger immune system.

Did you know the gut is sometimes called the “second brain”?

A healthy gut is also said to help with a more stable mood and better sleep quality.

When you drop the habit of eating late at night, your stomach and intestines spend less of the night busy with digestion, and some people find they wake up feeling lighter in the morning.

4. Steadier Blood Sugar Means Less Sleepiness After Meals

Setting fixed mealtimes makes sharp rises and drops in blood sugar after eating (known as blood sugar spikes) less likely.

It has been reported that when the release of insulin (the hormone that lowers blood sugar) stabilizes, your body becomes less prone to storing fat, and at the same time, post-meal sleepiness and sluggishness ease up.

There are also reports that time-restricted eating has improved how well insulin works (insulin sensitivity).

5. You Can Reset the Habit of Mindless Grazing

It’s often overlooked, but simply setting fixed eating times has real value in itself.

Habits like “eating because my mouth feels bored” or “nibbling snacks while watching TV” naturally fade just by having a rule about time.

Another welcome change is that you start being able to tell real hunger apart from simple boredom eating.

The Right Way to Do 16-Hour Fasting: 5 Steps for Beginners

Step 1: Start by Getting Used to 12 Hours

There’s no need to insist on 16 hours from the very start.

If you jump straight into 16 hours, the hunger can be tough, and you’re more likely to give up.

Step 2: Choose Your 8-Hour Eating Window

Next, choose your “8-hour eating window” to fit your daily rhythm.

It’s important to think about your work schedule and family mealtimes and pick a window you can stick to without strain.

Keeping it at roughly the same time each day makes it easier for your body’s rhythm to settle in.

For example, if you decide on “lunch at noon, a light snack at 4 p.m., and dinner finished by 7:30 p.m.,” you’ll never have to second-guess yourself.

The more specific your rules are, the less stress you’ll have from wondering “What should I do today?”

Step 3: Stay Well Hydrated During Your Fasting Hours

Even during your no-eating hours, it’s fine to have calorie-free drinks like water or tea.

It’s said that some of what feels like hunger is actually thirst in disguise.

Just drinking fluids regularly can sometimes ease your hunger.

Step 4: Make Your First Meal After the Fast Count

Whichever pattern you choose, start your first meal after the fast with something easy to digest.

Miso soup, vegetable soup, and yogurt are good choices.

If you wolf down greasy or sugary foods on an empty stomach, your blood sugar shoots up and your body becomes more likely to store fat.

It would be a shame to waste all 16 hours of effort, so make that first bite count.

I explain how to choose your first meal after a fast in detail in “Stabilize Your Blood Sugar with Your First Meal After a 16-Hour Fast: Foods That Help Promote Fat Burning.”

Step 5: Focus on Protein During Your Eating Window

It’s also important to make a point of getting enough protein during your eating window.

Making a habit of eating foods like chicken breast, eggs, tofu, and natto (fermented soybeans) helps prevent muscle breakdown and keep your metabolism going.

Getting plenty of fiber from vegetables and mushrooms also helps you stay full longer.

I recommend jotting down your weight and the times you ate, since it helps you find the pace that suits you.

How to Choose and Follow the Fasting Schedule That Fits You

3 Common Patterns

16-hour fasting can be broadly divided into three patterns depending on where you place your 8-hour eating window.

The Skip-Breakfast Pattern: “Eat from 12 p.m. to 8 p.m.”

In this pattern, you finish dinner by 8 p.m. and start eating again at noon the next day.

It suits people who “aren’t very hungry in the morning” and people who want to eat proper lunches and dinners.

It’s the most popular approach and the easiest one to get started with.

Its big strength is that you can still enjoy dinners out and evening meals with your family, so it fits in easily with your social life.

The Early-Dinner Pattern: “Eat from 7 a.m. to 3 p.m.”

In this pattern, you eat breakfast at 7 a.m. and finish lunch by 3 p.m.

It’s recommended for people who want to break the habit of eating late at night and for morning people.

It also works well for people who tend to snack after dinner.

Eating late at night is said to easily throw off your body clock, so this pattern is also a good fit for people who want to prioritize their circadian rhythm.

If You Work Shifts or Have an Irregular Schedule

If you work nights or rotating shifts, it’s best to think in terms of “from when you wake up to when you go to bed” rather than the time on the clock.

If you have your first meal a few hours after waking and finish eating within 8 hours of that, it becomes easier to create a 16-hour fasting period.

What About Days Off and Dinners Out?

On days off, you might wake up later, or dinner might run late because of eating out or drinks with friends.

What matters isn’t aiming for perfection day by day, but whether you’re securing enough “no-eating time” over the course of the week.

If you can’t decide whether skipping breakfast or eating dinner earlier will be easier to stick with, also take a look at “For Beginners: The 16:8 Fasting Method, a Basic Guide to Intermittent Fasting.”

What You Can and Can’t Drink While Fasting: Is Coffee OK?

Calorie-Free Drinks Are OK

There are some things you can drink even while fasting.

Water, sparkling water, unsweetened tea, black coffee, and other calorie-free drinks are OK.

On the other hand, sugary juices and caffè lattes are off-limits.

Be careful, because these get in the way of the benefits of fasting.

Black Coffee Is Fine to Drink

During 16-hour fasting, coffee is considered fine as long as it’s black, with no sugar or milk.

Some people find that the aroma and bitterness of coffee help take the edge off their hunger.

However, some people find that drinking coffee on an empty stomach easily upsets their stomach.

Too much caffeine can lower your sleep quality, so it’s a good idea to go easy on it from the late afternoon on.

If you really want to add milk, keep it to just a splash.

Gray-Zone Drinks That Are Easy to Get Confused About

Drinks that are easy to get confused about include protein shakes, soy milk, vegetable juice, and zero-calorie drinks.

Protein shakes, soy milk, and vegetable juice contain calories and carbohydrates, so have them during your 8-hour eating window rather than your fasting hours.

Zero-calorie drinks with artificial sweeteners contain almost no calories, but for some people the sweet taste stimulates their appetite.

It’s best to stick mainly to water and tea and think of zero-calorie drinks as just “a helping hand when things get really tough.”

Alcohol contains calories and also tends to increase your appetite, so it isn’t suited to your fasting hours.

Watch Out for Low Fluids and Minerals

Because you also get water and salt from food, you can easily end up short on fluids and minerals during your no-eating hours.

Even while fasting, aim to drink about 2 liters of water a day.

If you get a headache or feel dizzy, it might be a sign of dehydration.

Rather than drinking a lot at once, it’s gentler on your body to spread it out, one glass at a time.

During your eating window, make sure to replenish a moderate amount of salt as well, for example with miso soup.

I go into more detail on how to choose drinks in “What Can You Drink While Fasting? Enjoy a Comfortable IF Lifestyle with Water, Tea, and Coffee.”

Precautions to Know Before You Start, and Who It Isn’t Right For

People Who Should Hold Off or Consult a Doctor First

16-hour fasting is beneficial for many people, but it isn’t the right fit for everyone.

If any of the following apply to you, be sure to consult a doctor before you start.

Women in particular need to be careful.

Long fasts can affect the release of female hormones, which may lead to irregular periods or make feeling cold worse.

If you’re a woman, start with 12- to 14-hour fasts first, and gradually extend the time while keeping an eye on how your body responds.

If you’d like a detailed comparison of the pros and cons, also read “An Honest Look at the Pros and Cons of Fasting: What You Should Know Before You Start.”

4 Points to Keep in Mind While You’re Doing It

Likewise, on days when you’re tired, it’s perfectly fine to take a break instead of pushing yourself.

The secret to sticking with it long term is to approach it flexibly rather than pressuring yourself with “I have to keep going.”

3 Common Reasons People Don’t Lose Weight

If you’ve been doing 16-hour fasting but your weight isn’t changing, the following could be the reasons.

16-hour fasting is “a method for deciding when you eat,” not “a method where you can eat anything as long as it’s within 8 hours.”

Your weight also goes up and down due to things like water retention, so it’s important to look at changes over weeks rather than days.

After you’ve kept it up for a while, you may hit a “plateau” where your weight stops dropping.

A plateau is also said to be a sign that your body is adjusting to its new state, so don’t panic and cut back on food too much.

Common Discomforts When You’re Just Getting Started

When you’re just starting out, you may experience hunger, headaches, sluggishness, irritability, constipation, and so on.

Most of these are temporary and happen because your body isn’t used to the new rhythm yet, but there’s no need to push through them too hard.

Frequently Asked Questions About 16-Hour Fasting

Start Improving Your Health with 16-Hour Fasting Today

Start Easy with a 12-Hour Fast

16-hour fasting is a self-care habit you can start “just by creating time when you don’t eat,” with no complicated food restrictions.

By keeping it up, you can notice a variety of changes, such as activated autophagy, fat burning, a healthier gut environment, and steadier blood sugar.

There’s no need to insist on 16 hours from the very start.

The trick to sticking with it without strain is to let your body adjust with a 12-hour fast first, then gradually extend the time.

It’s fine if you can’t do it every day; your body will change even if you only keep it up a few times a week.

What matters most is listening to your body and keeping it up in a way that’s enjoyable and doesn’t feel forced.

I’ve summarized the overall approach to intermittent fasting in “2 Super-Simple Habits for Better Health: Intermittent Fasting for a Better Metabolism and Weight Loss.”

Why not start your fasting journey tonight by finishing dinner a little earlier?