Fasting Benefits by Hour – A Comprehensive Guide

The number of hours that you fast is one of the factors that may affect the benefits you get from fasting. There are some benefits that you’re likely to get, even within the first few hours of fasting, while others may take more time. It’s also important to note that the fasting benefits by hour may also be affected by other factors such as: 

• Physical Activity 

When you incorporate exercises and fast, your body will deplete the glycogen stores faster and enter a state of ketosis faster, which some people see as a benefit. 

• Food You Ate Before Fasting 

If you’re aiming to get into ketosis, a low-carb diet can help you reach ketosis faster while high-carb ones delay ketosis (1). If you’re fasting to lose weight, the number of calories you consume during your eating periods will directly affect your energy balance and therefore, your weight loss progress. Therefore, the type and amount of food you eat before fasting will also determine whether you’ll realize the benefits faster or you may need to take more time. 

• Type of Fast 

The type of fast will also affect the duration it will take for certain benefits to manifest. For example, with extended fasts, it is thought that autophagy is increased.

One of the most popular methods of intermittent fasting where hours count is the 16/8 method. With this method, you fast for 16 hours each day and only eat during an 8-hour window. Many people find it easy to implement as it is as simple as skipping breakfast or dinner. This type of fasting can reduce your overall calorie intake and many people find that they can maintain it for a long enough period to see some weight loss. 

• Body Fat Percentage 

Fat is stored energy that the body can tap into during a fast after glycogen stores have been exhausted or depleted. More fats in the body can affect how quickly weight loss goals are reached.

What Are Fasting Benefits by Hour?

It’s not possible to definitively pinpoint the benefits that you get on a per-hour basis throughout your fasting period. Quality evidence in humans is lacking, and it is likely that individual factors influence the way your body responds to a fast. The definition of fasting can also vary. It could be a single continuous fast or a daily routine with a window for fasting hours and an eating window as in intermittent fasting. It could also be alternate day fasting depending on your preference. Fasting could mean allowing a limited number of calories, or it may mean only water.

What most people care about in fasting is to see their desired results. For example, if you want to manage your weight, you may be able to achieve that over time with intermittent fasting or any other that is suitable to your individual needs. Most of the weight loss and resulting metabolic benefits happen with regular fasting over time, as it reduces your overall calorie intake. What matters is the reduction in calorie intake over a long period of time (i.e. months), rather than the duration in hours of an individual fast. 

As previously mentioned, there are some adaptations in the body that are believed to happen within the first few hours of fasting and some that may take more time, but it’s difficult to link these to any meaningful immediate benefits. The benefits by hour are also affected by individual factors, but generally, here are the metabolic adaptations that are thought to happen and their approximate timelines: 

• • 4-6 hours – the first thing that happens is a reduction in insulin and blood sugar levels. This happens after the body uses up the glucose that was taken in at the last meal. 
  • 8-12 hours – at this time, the body is probably tapping into its glucose stores, breaking down glycogen, and also starts to break down fats to supplement the energy needs. 
  • 12-16 hours – the body may go to the state of ketogenesis where glycogen is running low and more fat burning occurs. At this point, the process of autophagy (cellular repair process) is also believed to increase. 
  • 16-24 hours – fat burning continues as autophagy may also accelerate.
  • 24-48 hours – this is a reasonably long period that is believed to trigger significant metabolic adaptations in the body. Glycogen stores are most likely depleted and your primary energy source would be stored fat. Some muscle tissue may also be broken down to meet protein needs for essential functions.

With the duration and adaptations mentioned, it’s important to know how long you want to fast and to set your goal based on the changes that happen with time. 

What Is the Best Hour for Fasting?

There’s no universal time that fits everyone when it comes to choosing a time to start and end your fast. It all depends on some factors that include: 

• Health Goals 

Your health goals or what you want to achieve by fasting will also affect the timing. Some of these goals would include things such as weight management, controlling blood sugar, or improving insulin sensitivity. These are things that happen with consistent calorie reduction over time, so it’s important to choose a schedule that helps you achieve this and that you can stick with for a long enough period of time. 

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• Personal Preference 

Personal preference also plays a crucial role in determining the best hour to fast. For example, some people may find it incredibly difficult to skip breakfast while others can do so without harm. Therefore, it’s important to always listen to your body to understand the time that you can comfortably handle the fast. 

• Lifestyle and Work 

Your lifestyle and work can affect the way you fast. You may want to align your eating window with your working hours, exercise schedule, or social calendar. You’re more likely to succeed if fasting doesn’t interfere with things that are important to you or bring you joy.

• Circadian Rhythm Alignment 

Fasting that aligns with your body’s internal clock could also be best suited to your lifestyle and more beneficial for your metabolic health. 

• Hunger Patterns 

People have different patterns when it comes to hunger. Some people feel most hungry in the morning when they wake up, others in the afternoons, and others at night. This also influences the best time to fast as it won’t be practical to fast when you’re at your hungriest. For people who don’t tend to be hungry first thing in the morning, skipping breakfast would be easiest for them. 

It’s important to note that the best hour for fasting is different from one individual to another based on the factors we’ve mentioned above. Therefore, the one that is ‘best’ is the one that suits your lifestyle and can easily adapt and consistently maintain. 

While there’s no best time that universally suits everyone, you need to start slowly while listening to your body in whatever hour you choose to fast. During your eating days or window, ensure your diet is balanced and always stay hydrated while fasting. 

Read more: The Ultimate Fasting Mimicking Diet Food List For Beginners

How Many Hours of Fasting to Get Benefits?

The number of hours you should fast to get benefits depends on your individual goals or the benefits you want to achieve and also individual response. For example, if you’re interested in improving your metabolic flexibility, you’ll probably want to spend some time in the state where your body switches to alternative fuel sources, which is believed to happen beyond 12 hours or so of fasting (2). If you’re looking for weight loss and any resulting metabolic health improvements, you’ll need to choose a timeframe that helps you reduce your overall calorie intake and that you can stick to in the long term, which will look different for different people. 

So, you may realize some benefits of fasting from as early as 12 hours. The benefits that may come with the duration of fasting can be different, as follows: 

Is 12-Hour Fasting as Effective as 16?

A 12-hour fast may provide the body with a few potential benefits such as digestive rest, temporarily reduced insulin levels, and some mild metabolic adaptations. On the other hand, a 16-hour fast may be more beneficial as it triggers a more significant metabolic shift and the possible activation of autophagy. 

Here’s a more detailed explanation: 

• 12-Hour Fast – this type of fast will allow the body to process the food that you consumed during the day while you sleep. It also provides a break or rest in the digestive system. Therefore, it’s a good starting point for beginners or those who are new to fasting. 
• 16-Hour Fast – 16 hours is a bit longer duration and you may see some more significant benefits than you would in a 12-hour fast. With the extended period of fasting, the body depletes glycogen stores and resorts to burning fats for energy. It’s also a longer period that gives more time for the cellular repair process or autophagy to increase. In addition, most people find that limiting their eating window to 8 hours is more likely to result in a reduction in overall calorie intake, which can promote weight loss and resulting metabolic health benefits. 

Therefore, both 12-hour and 16-hour fasts may be beneficial, but suitable for achieving different goals. Effectiveness is also dependent on the goal you want to achieve. 

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Why Is 16 Hours the Magic Number for Fasting?

The popular 16-hour and magic number originates from the 16/8 intermittent fasting method where you fast for 16 hours and eat all your meals within the 8-hour window. It has become a popular method and many people think of it as a magic number due to the following: 

• Metabolic Switching – the 16-hour fast is long enough for glycogen stores to get depleted and for the body to switch to burning fats for energy or to enter ketosis. 
• Decreased Insulin Levels – the 16-hour period is enough to cause a significant drop in insulin levels. 
• Autophagy – this is thought to be the time where it starts to increase or where the body starts to remove some damaged cells. 
• Easy to Implement – the 16-hour fast is a magic number as it’s fairly easy to implement. Fasting for 16 hours is even easier for beginners as it’s not too long and it’s easy to achieve by just skipping breakfast or dinner. It’s also more sustainable than longer fasting periods. 
• Noticeable Changes or Benefits – most people find that fasting for 16 hours and limiting their eating window to 8 hours results in a reduction in overall calorie intake. This can promote weight loss over time, which in turn can have metabolic health benefits such as improved blood sugar, blood pressure, and blood lipid levels, in addition to a reduction in inflammation. These are some of the most noticeable and measurable benefits of intermittent fasting.  

Read more: Fasting 20 Hours Benefits: Impact on Health and Well-Being

Which Meal Is Best to Skip for Intermittent Fasting?

There’s no one meal that we can say is the best to skip or one that applies to everyone. This is because people have different lifestyles, personal preferences, and hunger patterns. Therefore, to know which meal is best to skip, it would be best to understand the pros and cons of skipping each meal. Of course, if your aim is to limit the number of calories you consume, you can start by eliminating morning and evening snacks if it’s a normal part of your meals. Here are the pros and cons: 

Skipping Breakfast 

Pros 

• Easiest meal to skip and convenient for many people who aren’t always hungry in the morning. 
• Just extends the natural overnight fasting, so it doesn’t disrupt your eating habits. 
• May align with those who want to exercise while on fast, especially in the morning hours. 
• Aligns with the circadian rhythm. 

Cons 

• May lead to increased hunger and overeating afterward. 

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Skipping Lunch 

Pros 

• Can work when you have a heavy dinner and breakfast. 
• Reduces the overall calorie intake if you don’t compensate later. 

Cons 

• May lead to afternoon energy crashes. 
• May cause you to overeat dinner due to increased hunger.
• Results in shorter fasting periods 

Skipping Dinner 

Pros 

• Good for those who want a longer fasting period before sleeping. 
• May also eliminate the usually unhealthy snacking after dinner. 

Cons 

• Dinner is a family meal and is socially challenging to skip. 
• May cause sleep disturbance due to increased hunger during the night. 

Frequently Asked Questions

• Is fasting good for your liver?

Researchers have suggested that fasting may help improve the functioning of the liver and may also lead to a reduction in accumulated liver fat. It may also help reduce inflammation in the liver (3). However, if you have impaired liver function or any other health condition, always talk to your healthcare provider before you start a fasting regimen. 

• Where do you lose weight first?

There’s no single answer to this. Where you lose fat first is dependent on several factors, including sex, age, and genetics. Where your body stores most of the fats is a matter of genetics and that’s where you’re likely to start losing fat. 

• How do you flush out water weight?

To flush out water weight, you may need to implement some changes in your diet. You may need to increase your consumption of potassium, reduce simple carbs, reduce sodium, and drink plenty of water. In addition, you need to increase the amount of physical exercise you do. However, if your water retention is due to a health condition, talk to your healthcare provider before you try any of these or other methods on your own.

• What is better than intermittent fasting?

Fasting works for weight loss as it reduces the overall number of calories you take in. That being said, fasting isn’t for everyone. You can achieve a reduction in calorie intake in plenty of other ways that may be easier and healthier than fasting. A healthy, balanced diet that is focused on fruits, vegetables, whole grains, legumes, lean proteins, and healthy fats is a great way to go. With calorie reduction plus increased physical activity, you’re likely to achieve similar benefits. 

The Bottom Line 

At this point, you now understand the benefits of fasting by hour. You’ve noted that some benefits come faster than others because when you fast, your body uses glycogen stores until when it is depleted, it resorts to using stored fats. 

Therefore, there are adaptations that you realize from as little as 4 hours into fasting, but some may take more than 12 hours. For example, ketosis and autophagy may take longer and also depending on your physical activity levels, the food you ate before fasting, your metabolic health, and the amount of fats in your body, among other factors. The type and duration of fasting that’s most likely to benefit you is whatever helps you reduce your overall calorie intake and that you can stick to long enough to lose some weight. Always talk to your healthcare provider before you start any fasting regimen.