What is 20:4 Intermittent Fasting?
Intermittent fasting, also known as time-restricted feeding, is a type of diet where you fast from food for a set number of hours in one day. 20:4 intermittent fasting means that the fasting window extends for 20 hours, leaving you with 4 hours to eat.
For example, to follow a 20:4 fasting schedule, if you ate your last meal by 4 PM, you would fast until 12 PM the following day. Then you would eat your meals between 12 PM to 4 PM. In this case, you would skip breakfast, and your first meal of the day would be lunch.
While it may take some getting used to, it doesn’t seem to be a difficult diet, considering it is not a calorie-restrictive diet. In fact, you can eat as much as you want within the 4-hour window as you please (within reason, of course, more to come on this).
How to Do 20:4 Intermittent Fasting
Intermittent fasting 20/4 is flexible. While you do have to fast for 20 hours each day, your 4-hour eating window is flexible and can occur at any time that makes sense for your schedule. While some may choose to skip breakfast by only eating between 12 PM and 4 PM, you may find that eating between 10 AM and 2 PM works better for you.
Fasting for 20 hours may take some time to get used to. If you feel like you need to ease yourself into a fasting diet, you can. There is no rush to fast for 20 hours when your body is not accustomed to fasting. You can gradually increase the number of hours that you fast every week. If you currently fast for 13 hours over the evening and through the night on a natural occurrence, you could begin fasting for 14 hours and slowly increase the duration as you see fit. Research has not solidified the best number of hours that you need to fast to obtain benefits . So, easing yourself in will not cause any harm . It may even help you maintain your fast longer.
What Can You Eat?
The 20:4 intermittent fasting diet does not specify what to eat, only when to eat. But, this does not mean that you should eat as much junk food as you wish to within your eating window. That would definitely hinder you from experiencing any potential benefits of fasting.
Intermittent fasting is also not meant to be calorie-restrictive, meaning that you should still eat the recommended amount of calories within your eating window. The USDA’s Dietary Guidelines for Americans state that males between the ages of 19 through 30 should eat between 2,400 to 3,000 calories per day, depending on their individual caloric needs . Females of the same age need to consume between 1,800 to 2,400 calories per day, depending on their caloric needs . The USDA also recommends that people eat a diet rich in fruits, vegetables, dark leafy greens, whole grains, and protein . While also limiting refined grains, added sugars, saturated fats, sodium, and alcoholic beverages . When 20/4 intermittent fasting, eating a healthy diet is necessary if you want to experience the potential benefits of fasting.
During the fasting hours, it is important to stay hydrated. When fasting, you are allowed to consume any beverages, including water, coffee, and tea, as long as they are zero-calorie beverages .
Potential Benefits of 20:4 Intermittent Fasting
Weight loss is the main benefit that people attribute to intermittent fasting. Typically, people eat three meals a day and snacks between meals and in the evening. In this case, the body receives energy from the constant consumption of food . When intermittent fasting, after your body burns through the energy from the last meal, you enter a fasting state where your body will burn energy from fat stores instead [3, 5]. This may be what leads many people to experience weight loss when intermittent fasting and eating nutritious foods.
However, some studies show that people who participate in intermittent fasting do not lose any more weight than those who are on a calorie-restricted diet [5, 7, 8, 11]. This means that it may not be the fasting that leads to weight loss but the caloric deficit that many people reach when fasting .
For example, when 20:4 intermittent fasting, it may be difficult to eat your recommended daily intake of calories in 4 hours. If you need to eat 2,200 calories per day, but you can only eat 1,800 calories in your four-hour window, you would experience weight loss. This weight loss would be more likely to contribute to the caloric deficit than fasting itself.
Lean Muscle Retention
You may be wondering, if fasting 20:4 may cause you to lose weight, will you lose muscle mass or strength as well? One study conducted a trial to find out. They found that intermittent fasting did not affect lean muscle retention in young males as long as they met their daily recommended caloric intake .
Improved Glycemic Response
Intermittent fasting may also improve fasting glucose in individuals with type 2 diabetes or prediabetes [9, 10].
One study found that individuals with type 2 diabetes who fasted twice a week had improved fasting glucose . However, they also found that individuals with type 2 diabetes should fast with caution, especially those on glucose-lowering medications because they can experience hypoglycemia . The benefit compared to the risk, in this case, is inconclusive.
Another study found that men with prediabetes who intermittently fasted while eating their daily recommended calorie intake had improved insulin sensitivity and cell responsiveness . Many other trials also suggest that intermittent fasting is more effective in lowering insulin levels than lowering glucose .
While more research is needed on this topic, there may be benefits found here.
Protection Against Chronic Disease
Intermittent fasting may also help protect you from developing chronic diseases. While studies are limited, some have found that consuming calories in the early part of the day and fasting at night for longer durations may reduce the risk of chronic diseases in improving cardiac health [1, 12].
While it may seem that fasting for 20 hours of the day would lead to feeling hungry, studies show that fasting does not increase hunger as long as you eat enough calories during your 4-hour eating window . If you make sure that you are eating your recommended daily caloric intake, then your body will have been provided enough energy to carry itself through the day.
Many studies have observed that nighttime eating has a negative effect on sleep duration and quality . Following a 20:4 intermittent fasting plan would reduce nighttime eating, which may improve your sleep .
Potential Risks of 20:4 Intermittent Fasting
Individuals with type 2 diabetes should be cautious about beginning intermittent fasting, especially 20:4 intermittent fasting since it is a long fasting period. Intermittent fasting greatly increases the risk of hypoglycemia [1, 4, 9]. An even greater risk of hypoglycemia is posed for those who take glucose-lowering medications [1,9].
Intermittent fasting is not recommended for individuals who have been diagnosed with eating disorders of any form [1, 4]. Even though 20:4 intermittent fasting is not a calorie-restrictive diet, only time restrictive, those with anorexia or bulimia nervosa should be cautious as following the diet may increase self-restriction .
It may also place a person at risk for overeating during their eating window because the fasting period can increase an individual’s fixation on food .
20:4 intermittent fasting is not recommended for anyone in an active growth stage of life, such as adolescents who need to consume calories throughout the day to maintain proper growth . Individuals who are pregnant or breastfeeding should also avoid intermittent fasting .
Anyone with preexisting health conditions or chronic diseases should seek a professional opinion before attempting 20:4 intermittent fasting as there could be undesirable or harmful side effects .
Is it good to fast for 20 hours a day?
While some research shows the potential benefits of fasting 20 hours a day, there is still not enough research to state that fasting for 20 hours a day is necessarily a good thing. The good news is that for healthy individuals, there is a very low risk of harm from fasting 20 hours a day .
Can you do 20:4 fasting every day?
You could do 20:4 fasting every day, but it may not be sustainable for longer than a few days in a row or a few weeks at most.
Does coffee break a fast?
Good news! As long as you drink your coffee black, it does not break your fast. Adding cream and sugar will break your fast.
How soon will I see the results of 20:4 intermittent fasting?
If you are looking for weight loss results, many factors play into seeing results from 20:4 intermittent fasting. Are you eating in a caloric deficit? Are you eating healthy, nutritious foods in your eating window? Are you engaging in daily physical activity? If you are, then you may see results of weight loss in a matter of a few weeks.
If you are looking for a fasting diet, 20:4 intermittent fasting may be a good option. Just make sure that you fully evaluate the potential benefits and risks in order to determine if it is right for you. There are some benefits that scientific research shows can come from intermittent fasting. However, more research is still needed in many areas. It is also not considered safe if you have any pre-existing health conditions or chronic diseases such as type 2 diabetes.
Whenever you are looking to begin a new diet, make sure that you consult with your primary physician or a registered dietitian before beginning.
- Horne, B. D. (2020). Considerations for the Optimal Timing, Duration, Frequency, and Length of an Intermittent Fasting Regimen for Health Improvement. Nutrients, 12(9), 2567. https://doi.org/10.3390/nu12092567
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition.
- Johns Hopkins Medicine. (2022, March 7). Intermittent Fasting: What is it, and how does it work? https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work
- Harvard: School of Public Health. (2022, May 17). Diet Review: Intermittent Fasting for Weight Loss. The Nutrition Source. https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting/
- Collier, R. (2013). Intermittent fasting: the science of going without. Canadian Medical Association Journal, 185(9), E363–E364. https://doi.org/10.1503/cmaj.109-4451
- Tinsley, G. M., Forsse, J. S., Butler, N. K., Paoli, A., Bane, A. A., La Bounty, P. M., Morgan, G. B., & Grandjean, P. W. (2016). Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European Journal of Sport Science, 17(2), 200–207. https://doi.org/10.1080/17461391.2016.1223173
- Harris, L., Hamilton, S., Azevedo, L. B., Olajide, J., de Brún, C., Waller, G., Whittaker, V., Sharp, T., Lean, M., Hankey, C., & Ells, L. (2018). Intermittent fasting interventions for treatment of overweight and obesity in adults. JBI Database of Systematic Reviews and Implementation Reports, 16(2), 507–547. https://doi.org/10.11124/jbisrir-2016-003248
- Seimon, R. V., Roekenes, J. A., Zibellini, J., Zhu, B., Gibson, A. A., Hills, A. P., Wood, R. E., King, N. A., Byrne, N. M., & Sainsbury, A. (2015). Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Molecular and Cellular Endocrinology, 418, 153–172. https://doi.org/10.1016/j.mce.2015.09.014
- Corley, B. T., Carroll, R. W., Hall, R. M., Weatherall, M., Parry-Strong, A., & Krebs, J. D. (2018). Intermittent fasting in Type 2 diabetes mellitus and the risk of hypoglycaemia: a randomized controlled trial. Diabetic Medicine, 35(5), 588–594. https://doi.org/10.1111/dme.13595
- Sutton, E. F., Beyl, R., Early, K. S., Cefalu, W. T., Ravussin, E., & Peterson, C. M. (2018). Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism, 27(6), 1212–1221.e3. https://doi.org/10.1016/j.cmet.2018.04.010
- Cho, Y., Hong, N., Kim, K. W., Cho, S., Lee, M., Lee, Y. H., Lee, Y. H., Kang, E., Cha, B. S., & Lee, B. W. (2019). The Effectiveness of Intermittent Fasting to Reduce Body Mass Index and Glucose Metabolism: A Systematic Review and Meta-Analysis. Journal of Clinical Medicine, 8(10), 1645. https://doi.org/10.3390/jcm8101645
- Patterson, R. E., & Sears, D. D. (2017). Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition, 37(1), 371–393. https://doi.org/10.1146/annurev-nutr-071816-064634