20:4 Fasting: How To Decide If It's Right For You + Easier Alternatives
20:4 fasting, also known as the Warrior Diet, is an advanced form of intermittent fasting that may be difficult for beginners. Here's what you need to know about the benefits and risks of 20:4 fasting, whether it's safe, as well as some easier alternatives.
What is the 20:4 fasting method?
20:4 fasting involves fasting for 20 hours per day and eating during a four-hour window. It is a type of intermittent fasting that is categorized as time-restricted eating (TRE), where the focus is on when you can and cannot eat rather than what you can and cannot eat.
20:4 fasting was popularized by the book The Warrior Diet by Ori Hofmekler. The book is based on Hofmekler's experiences of staying fit while in the Israeli special forces by practicing the lifestyle habits of ancient warriors, who typically ate little to nothing during the day, exercised vigorously, and then feasted at night.
While the strict version of this fast requires you to limit yourself to water and other calorie-free beverages during the fasting window, modified versions allow you to eat small portions of foods such as fruits, vegetables, dairy, and hard-boiled eggs during the fasting window to keep you going.
When you fast for 20 hours a day, your body goes into a metabolic state known as ketosis1, where it starts to tap into stored fat for energy. This fasting state can help promote weight loss2, in addition to offering other cardiometabolic benefits3, such as reduced blood glucose, blood pressure, and cholesterol, says Madiha Saeed, M.D., an integrative family physician and author of The Holistic Rx.
"Longer fasts also enable autophagy, which helps your body detox and repair itself," Saeed adds.
The 20:4 fasting protocol doesn't restrict any food groups and doesn't require you to count your macros. Modified versions also allow you to choose the timing of your fasting window.
However, some people may find it hard to fast for 20 hours at a time. Intermittent fasting beginners may find it easier to start with a less restrictive fasting regimen instead.
Benefits of 20:4 fasting
While there are many research studies documenting the benefits of intermittent fasting and time-restricted feeding, few pertain specifically to 20:4 fasting.
However, a few early studies show that the eating pattern offers health benefits such as improved cardiometabolic health, reduced blood sugar levels, and more efficient cell repair and rejuvenation.
It may improve cardiometabolic health.
A comprehensive review covering 46 studies concluded that intermittent fasting can help improve several cardiometabolic markers4 such as weight, body mass index (BMI), blood pressure, cholesterol, and triglyceride levels.
Furthermore, a randomized controlled trial that specifically tested the benefits of 20:4 fasting found that it also helped improve cardiometabolic health by reducing inflammation and oxidative stress2, which can be harmful to your heart5 and contribute to the development of chronic diseases.
It may help regulate blood glucose.
A review published in the Journal of the Academy of Nutrition and Dietetics notes that fasting for 20-hour intervals can help lower blood glucose levels6. This happens because fasting reduces the amount of glucose synthesized by the liver and helps the body use glucose more efficiently3.
Maintaining healthy blood glucose levels is important because chronically high blood glucose levels can lead to severe health conditions, such as diabetes, kidney disease, nerve damage, heart disease, or stroke.
It may promote cell repair and rejuvenation.
A 2019 study found that time-restricted eating promotes autophagy7, which is a natural housekeeping process by which your body repairs, recycles, or disposes of damaged cells.
Autophagy generally kicks in after 17 hours of fasting, says Saeed. "It's a hyperactive healing state where your body detoxes itself and repairs mitochondrial damage."
In this state, your body accelerates the process by which it repairs damaged DNA molecules and produces antioxidants to fight off harmful free radicals, Steve Hendricks, author of The Oldest Cure in the World: Adventures in the Art and Science of Fasting, previously told mindbodygreen.
Autophagy8 plays an important role in preventing health conditions such as cancer, neurodegenerative diseases, metabolic conditions, and infectious diseases.
Is 20:4 fasting effective for weight loss?
Yes, 20:4 fasting can help you lose weight, if that's your goal. A small randomized controlled trial with 11 overweight adult participants found that fasting for 20 hours per day for eight weeks helped participants lose approximately 3% of their body weight2.
Going without food for a period of time is a powerful way to boost metabolism, Chris Palmer, M.D., a Harvard psychiatrist, previously told mindbodygreen. In fact, research shows us that intermittent fasting can be as effective for weight loss9 as traditional diets that require you to limit your daily calorie intake.
However, it's important to keep in mind that fasting is not a miracle solution. Whether you lose weight, and how much weight you lose, will depend on what you eat on fasting and non-fasting days. Eating a lot of high-calorie junk food during your fasting window or on non-fasting days may even cause you to gain weight.
Other factors like your initial body weight, exercise, and stress levels can also play a role in how much weight you are able to lose, Laura DeCesaris, IFMCP, M.S., D.C., a functional medicine practitioner, previously told mindbodygreen.
Optimizing your feeding window
While the original Warrior Diet recommends eating your primary meal at night, other interpretations of the 20:4 fast give you the freedom to choose your feeding window. Depending on your lifestyle and personal preferences, you could choose to schedule it in the morning, afternoon, or evening.
For instance, if you wake up early and work out in the morning, you may choose to schedule your eating window to begin a little before your workout so you can fuel up before you exercise and refuel for the rest of the day. However, not being able to eat in the evening may put a damper on your social life.
On the other hand, if you're not a breakfast person and prefer to prolong your fasted state for as long as possible, you can schedule your feeding window in the afternoon or evening.
However, research shows that scheduling your eating window for earlier in the day tends to be a healthier choice. Doing so helps align your internal clock with the external cues of daylight, Humaira Jamshed, Ph.D., a researcher and assistant professor at the Dhanani School of Science and Engineering, previously told mindbodygreen. This is the best option for metabolic health10, weight loss11, blood glucose management7, and sleep12, according to Jamshed.
Tips for 20:4 fasting
These are some tips that can help you practice 20:4 fasting successfully:
If you've never fasted before, it can be difficult to suddenly fast for 20 hours at a time. Work your way up to it slowly, by starting with 12-hour, 16-hour, and 18-hour fasts before you get to a 20-hour fast. You can increase your fasting window gradually every week or every other week. Here's a starter guide to different types of fasts to help you find the best one for your needs.
Experiment with different schedules.
Try different meal combinations and timing options to see what works best for you. Within the four-hour feeding window, you can choose to eat one big meal or a couple of smaller meals with some snacks.
You can also experiment with the frequency of your fasts. For instance, instead of fasting every day, you can fast once or twice a week, says Saeed. This may be a more sustainable option in the long run.
Focus on nutritious foods.
In order to maximize your benefits from 20:4 fasting, it's important to focus on healthy, nutritious whole foods. Opt for fruits, vegetables, lean proteins, nuts, seeds, legumes, and healthy fats. Avoid processed foods, sugary foods and drinks, and trans fats.
Plan your meals ahead of time.
Planning your meals ahead of time can help ensure that you don't impulsively eat junk food during your feeding window simply because it's convenient and nothing else is available. Get creative with nutritious and delicious foods.
Make sure you drink plenty of water during the day to stay hydrated. You can also drink other calorie-free beverages such as green tea, black tea, black coffee, seltzer, or water flavored with lemon or cucumber.
Take vitamin and mineral supplements.
It can be helpful to take a daily multivitamin and mineral supplement every day to help meet your nutritional needs while you're fasting and reduce the risk of developing a nutrition deficiency, Bindiya Gandhi, M.D., an American Board–certified physician who practices family medicine and integrative medicine, previously told mindbodygreen.
Sample meal plan
Wondering how to load up on healthy food in such a short amount of time? Here are sample meal plans for different 20:4 feeding windows:
Early feeding window:
8 a.m.: Apple slices with nut butter
8:30 a.m.: Workout
9:30 a.m.: Avocado toast topped with a fried egg
11 a.m.: Blueberry smoothie
12 p.m.: Chicken and vegetable salad
Midday feeding window:
2 p.m.: Burrito bowl
3 p.m.: Yogurt with berries
4 p.m.: Kale chips
6 p.m.: Grilled salmon with salad
Evening feeding window:
4 p.m.: Lemon chicken with broccoli
5 p.m.: Fruit salad
6 p.m.: Mixed nuts
8 p.m.: Shrimp tacos
Safety & side effects
One major downside of a 20:4 fasting regimen is the risk of nutritional deficiencies. The less you eat, the fewer essential vitamins, minerals, and protein you get into your system. "It can be difficult to get adequate nutrition in such a small feeding window," says Saeed.
This fasting regimen may work for some people, but it's not safe for everyone. Children, pregnant or breastfeeding people, people with eating disorders, and people who are underweight should avoid this fasting protocol, Saeed states.
Saeed recommends that women and people who menstruate undertake this fasting regimen cautiously, since it can place considerable stress on the body and may affect fertility. It also may be too much for women who are postmenopausal.
Some of the other potential side effects of fasting13 include fatigue, hunger, irritability, low mood, difficulty concentrating, and obsessive food-related thoughts.
You should consult with a health care provider before you begin the 20:4 fasting protocol to determine whether it's appropriate for you and how you can practice it safely.
How long can you do it?
Because of its restrictive nature, this fasting protocol may not be ideal for the long term. Shorter feeding windows are generally linked to poorer adherence rates3.
How long you can practice this fast can vary from person to person, says Saeed. "Some people thrive on this eating schedule, but others suffer. So, listen to your body." If you ever get dehydrated, feel faint, or experience blood sugar instability, you should stop the fast.
If 20:4 fasting feels too restrictive for you to follow long term3, you can also try a different form of time-restrictive eating that gives you a larger feeding window. 16:8 fasting and 18:6 fasting are great options, says Saeed.
Is 20:4 a good intermittent fasting schedule?
20:4 fasting may be helpful if you've tried intermittent fasting before and feel up to doing a more advanced fast. It may not be suitable for beginners who are new to intermittent fasting.
Can you gain muscle while on the 20:4 fast?
Yes, you can gain muscle on the 20:4 fast, provided you get enough protein to meet your daily protein needs, says Saeed. She suggests working out while you're in the fasted state and then eating a protein-rich meal in order to help you build muscle.
How much weight can you lose on a 20:4 fast?
It depends on the person, but one study on overweight adults found that fasting for 20 hours per day for eight weeks helped participants lose approximately 3% of their body weight. If you're looking to lose weight while fasting, it's important to make sure your feeding windows are as nutritious as possible.
20:4 fasting is an advanced intermittent fasting protocol that requires you to fast or severely restrict your calories for 20 hours in a day. Emerging research shows us that staying in a fasted state for several hours may promote weight loss and offer other health benefits. This form of fasting may not be safe for everyone, so it's best to check with your health care provider whether it's appropriate for you.
If you're new to fasting, you should start with other, less restrictive types of intermittent fasting and work your way up to the 20:4 protocol.
Sanjana Gupta has been a health writer and editor since 2014. She has written extensively for platforms like Insider, Livestrong.com, and Verywell Mind. Her work spans various health-related topics, including nutrition, fitness, mental health, medical conditions, and wellness.
Sanjana has a master's degree in digital journalism from New York University. She also holds a master's degree in management from the University of Mumbai.
She balances her love for chocolate with a penchant for fun workouts like aerial yoga and kickboxing.