Blog Diets Fasting 5 Health Benefits of a 20-Hour Fast

5 Health Benefits of a 20-Hour Fast

In a world where wellness trends come and go, intermittent fasting has gained popularity. Every day, more health experts and fitness enthusiasts rely on fasting to provide multiple health benefits. 

While the most popular fasting option is the 16-hour fast, there are other options that are more appealing to those who prefer a shorter eating window. One of these is the 20-hour fast. 

But is the 20-hour fast dangerous? And most importantly, what are the benefits of a 20-hour fast vs a 16-hour fast?

Here, we will look at the five benefits of a 20-hour fast. We will determine if it’s a safe practice to follow and what the best way is to help you break your extended fast. 

What Is a 20-hour Fast?

A 20-hour fast is when you ingest all your daily calories during a four-hour eating window, leaving the remaining 20 hours as a fasting period. 

Through fasting, the body gradually depletes its glycogen stores, transitioning from a sugar-burning to a fat-burning mode. This metabolic state is known as ketosis and it is one of the multiple benefits of fasting.

In most cases, food is not allowed during fasting hours and only non-caloric beverages, such as tea, coffee, or water, are allowed. 

As a registered dietitian, I always like to point out that this type of fasting is not for beginners or those who haven’t tried fasting for more than 16 or 18 hours. So, if you’re new to fasting, it’s best to start with a less restrictive fasting protocol. 

Are you curious about the 20/4 fasting protocol? Find out more by reading our other article: Intermittent Fasting 20/4

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See also
What To Eat During Intermittent Fasting: How To Maintain The Benefits Of Your Fast

5 Benefits of a 20-hour Fast

If you fast for 20 hours a day, you may start to notice physical, mental, and other important health benefits. Here are some potential health benefits of a 20-hour fast. 

Improved Weight Loss

When you fast, your body’s insulin supply significantly drops, which allows fat cells to release stored sugar and fats. Therefore, one of the biggest benefits of a 20-hour fast is the effect it has on weight loss. 

It’s important to keep in mind that fasting for 20 hours is not a miracle cure. You still need to be in a caloric deficit to lose weight. So, if you’re fasting but still eating more than you require (caloric surplus), you’re less likely to lose weight. 

In a 2020 study (4), people managed to lose 3% of their body weight by doing a 20-hour fast because they had a calorie deficit (eating fewer calories than the body needs) of approximately 500 calories. 

For those who prefer bigger meals throughout the day, this type of fasting can be highly beneficial as a short eating window allows for 2-3 meals a day

Better Heart Health

Another big benefit is improved cardiovascular health. Evidence suggests that fasting can help reduce blood pressure, cholesterol, and triglycerides (3). 

In addition, fasting may also help reduce inflammation by reducing oxidative stress, which occurs when the body has too many free radicals to deal with (4). Too much inflammation in the body has been linked to an increased risk of chronic illnesses, such as heart disease (9). 

Hormone Regulation 

According to some studies, crucial hormones such as norepinephrine and growth hormone spike during a fast, which enhances the body’s ability to oxidize fat (6). 

Other important hormones, such as insulin, are regulated while fasting. A 20-hour fast may help reduce blood sugar levels, which reduces the risk of diabetes (8). This can improve the body’s ability to use glucose while fasting. 

See also
The 30-Day Fasting Challenge Explained: How to Kickstart Your Journey The Right Way

Remember that as fasting can severely lower your sugar levels, you should consult your health provider before making changes to your eating schedules if you have diabetes. 

benefits of a 20 hour fast  

Improved Brain Function 

There also seem to be potential cognitive benefits when fasting. Research has suggested that intermittent fasting may improve mental clarity and focus, partly due to brain-derived neurotrophic factor (BDNF) (7). 

You may be wondering what BDNF is.

BDNF-1 has been highly associated with brain cell creation. High levels of BNDF have been linked to improved learning and better cognitive function (2). While more research is still needed to determine why this happens while fasting, current research seems promising. 

Increased Longevity 

While current studies regarding fasting and longevity are limited, some studies have shown promising results with fasting and living longer. According to studies, calorie restriction may help enhance longevity, both in animals and humans (1). 

Read more: Why Stop Eating Oatmeal – A Breakfast Revolution

Is Fasting 20 for Hours a Day Good? 

As we’ve seen, doing a 20-hour fast can provide several health benefits to both the body and mind. However, a 20-hour fast is not suitable for everyone. 

People who need a higher caloric intake, such as athletes or those with physically demanding jobs, may not benefit from a 20-hour fast. In addition, pregnant or lactating women should not follow any fasting protocol as it can affect the health of the baby. 

It’s important to listen to your body’s needs and consult a health professional before you make significant changes to your diet. If you’re not ready to fast for 20 hours a day, you can do a 20-hour fast once a week to get its benefits. 

See also
The Vegetarian Intermittent Fasting Guide to Plant-Based Fasting and Feasting

Is 20 Hours of Fasting Enough for Autophagy? 

Autophagy is the process through which cells degrade and recycle damaged components. In other words, it’s the process in which the cells clean themselves when they’re going through a stressful time or not getting enough nutrients (such as when fasting). 

Most studies have shown that autophagy peaks during a fasting period between 18 and 24 hours, which suggests that a 20-hour fast promotes autophagy (10). However, to get the most out of this process, make sure your fasting period is followed by a diet that is rich in nutrients. 

Tips for Successfully Doing a 20-Hour Fast

Adhering to a 20-hour fast can be challenging, but with the right approach, you can make it a sustainable part of your lifestyle. 

Here is some of the advice I often give users to help them crush their fasting protocol:

  • Stay hydrated. Proper hydration is crucial during a fast. Water, coffee, herbal teas, and non-caloric beverages can help you fight feelings of hunger and support the body’s detoxification processes. 
  • Start with shorter fasts. As mentioned earlier, if you haven’t fasted for at least 16 to 18 hours, this fast is not for you. It is recommended to start with a 12-hour fast and slowly increase the fasting hours.
  • Choose the right eating window. One of the benefits of fasting is that there is no one-size-fits-all approach to it. Consider your work, social life, and other activities to help determine when the best times to fast and eat are. 
  • Plan your meals. To get the most out of your fasting, make sure you plan what you’re going to eat during the day. This will allow you to get all the nutrients your body needs in a short eating window. 
  • Monitor your body’s response. While fasting has several health benefits, it may not work for everyone. You should pay attention to your hunger, energy levels, and mood. If fasting is negatively affecting one of these areas, consider modifying your fasting schedule or protocol. 
See also
Intermittent Fasting and Running: A Winning Combination or a Terrible Mistake? 

If you need more help or information on how to do your fasting properly, you can check out our intermittent fasting guide

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What Is the Best Thing to Eat After Fasting for 20 Hours? 

As you have a short eating window, the foods you decide to include are going to play a crucial role in helping refuel your cells and get the most out of your 20-hour fast. 

Opting for easily digestible foods that are high in nutrients can ease your body back into the feeding state and prevent any digestive discomfort. 

The ideal post-fast meal includes a balance of macronutrients, such as lean proteins, healthy fats, and complex carbs. Options such as soups, smoothies, or well-portioned meals that contain a variety of vegetables, whole grains, and lean proteins are an excellent choice. 

Remember that proper hydration is essential and after a 20-hour fast, you should also focus on including hydrating foods and drinks that can help replenish your lost fluids and support your body’s functions. 

While you may not want to do it for its weight loss properties and more for its other health benefits, you should avoid overeating. 

After a long fast, the temptation can be strong. It’s important to listen to your body’s hunger cues and eat until you’re comfortably full, gradually increasing portion sizes as your body adapts to the fasting routine. 

See also
What Is the Best Fasting Schedule for You: Pros, Cons, and Everything in Between

Another good approach is to choose foods from the Mediterranean diet. These are often lean proteins, vegetables, fruits, and healthy fats that can help you effectively break your fast and provide tons of nutrients. 

benefits of a 20 hour fast  

What Are the Benefits of Fasting for 30 Hours?

A 30-hour fast, as the name suggests, means you fast for 30 hours straight. While this sounds challenging, several health benefits make it worth trying, including: 

  • Autophagy 
  • Improved insulin sensitivity
  • Weight management and fat loss
  • Mental clarity and focus
  • The promotion of longevity 

As you can see, there are similar benefits to those obtained from a 20-hour fast. Choose the one you feel most comfortable with and always speak to a health professional before you change your fasting hours. 

Fasting may not be suitable for everyone, particularly those with certain medical conditions and those who are breastfeeding or pregnant. 

Read more: Green Tea Intermittent Fasting: Benefits and Side Effects

benefits of a 20 hour fast  


  • Is 20:4 fasting more effective than 16:8?

The effectiveness of fasting is dependent on an individual’s goals and preferences. While a 20:4 fast may offer slightly more prolonged periods of fat burning, a 16:8 fast may be more manageable and sustainable. Both options can promote weight loss, improve insulin sensitivity, and offer countless health benefits. Choosing the fasting pattern that best aligns with your lifestyle and supports your overall wellness is important. 

  • Does fasting increase testosterone?

Fasting may slightly increase testosterone levels, but there is mixed evidence in support of this. Some studies have shown that testosterone levels decrease when fasting (5). More research is required to understand the long-term effects of fasting on testosterone levels. 

  • When does autophagy start?

According to some studies (10), autophagy may start at the 18-hour fasting mark. 

  • What happens after 21 hours of fasting?

After 21 hours of fasting, the body enters a long-term fasting state. There is an increase in ketone production, which leads to greater ketosis. This can result in weight loss, improved cognitive function, and better hormone balance. 

  • Is it OK to fast for 16 hours every day?

Yes, it’s ok to fast for 16 hours a day. However, before you make drastic changes, it’s important to consult a health professional and listen to your body. If you notice any negative effects, it’s best to make adjustments to your fasting. 

The Bottom Line

Intermittent fasting offers several health benefits. While a 20-hour fast is not for everyone, for those who commit to this fasting protocol, it may help promote weight loss, improved cognitive functions, and an enhanced sense of well-being. 

However, it’s important to approach fasting with knowledge, caution, and a willingness to adjust based on personal experience. Understanding the science behind fasting can empower you to make informed decisions about your health and potentially unlock 20/4 intermittent fasting weight loss benefits and other health benefits. 

Remember that it’s important to consult a health professional before you make any drastic changes to your nutrition. 


This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!


  1. A 2-Year Randomized Controlled Trial of Human Caloric Restriction: Feasibility and Effects on Predictors of Health Span and Longevity. (2015, Academic.oup)
  2. Brain-Derived Neurotrophic Factor in Brain Disorders: Focus on Neuroinflammation. (2019,
  3. Effect of Epidemic Intermittent Fasting on Cardiometabolic Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. (2021, pubmed)
  4. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity (2020, pubmed)
  5. Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials. (2022, pubmed)
  6. Influence of norepinephrine, growth hormone and fasting on FFA mobilization and glucose metabolism in lean and obese subjects. (1968, pubmed)
  7. Intermittent fasting and cognitive performance – Targeting BDNF as potential strategy to optimise brain health. (2022, ScienceDirect)
  8. Intermittent Fasting and Human Metabolic Health. (2015,
  9. Oxidative Stress and Inflammation in Heart Disease: Do Antioxidants Have a Role in Treatment and/or Prevention? (2011, pubmed)
  10. The Beneficial and Adverse Effects of Autophagic Response to Caloric Restriction and Fasting. (2023,
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