OMAD And 20:4 Intermittent Fasting
There are three similar intermittent fasting protocols that have quite short daily eating windows: 18:6, 20:4, and one-meal-a-day (OMAD). In general, these involve abstaining from calories for 18-23 hours a day, and then eating freely within the remaining time. The eating window can occur at any point of the day, but most people choose to eat between 2 p.m. and 8 p.m.
OMAD And 20:4 Intermittent Fasting is most often used for
As a note, the scientific community tends to restrict the term “intermittent fasting” to diets that drastically restrict calories for 2-4 days of the week (such as not eating at all for a day, or eating very few calories for a couple days of the week). For daily fasting of set durations, the term “time-restricted eating” is preferred. For the sake of this page, the terms will be used interchangeably.
Time-restricted eating is often described as the ratio of hours spent abstaining from food and the hours where eating is permitted.
In the 18:6, 20:4, and one-meal-a-day (OMAD) protocols, individuals abstain from any caloric intake for 18 to 23 hours a day and then eat freely for the rest of the day. Those who follow the OMAD protocol eat all their food at one sitting, which typically lasts an hour or less, while the other protocols typically involve more than one meal or a meal and a snack.
Colloquially, these types of eating schedules fall under the category of “intermittent fasting”, but in the scientific literature that term generally refers to eating schedules that involve abstaining from or drastically lowering energy intake for more than 24 hours. Time-restricted eating can involve a caloric deficit to lose weight, but doesn’t have to.
The 18:6, 20:4, and one-meal-a-day (OMAD) protocols are types of time-restricted eating where you abstain from eating for 18 to 23 hours, and then eat freely for the rest of the day. They can be combined with a caloric deficit for weight loss, but don’t have to be.
There aren’t many studies on these particular intermittent fasting regimens, and the findings are a bit contentious.
In general, they can be a viable method for weight loss when paired with a caloric deficit and may be easier to follow than a standard diet that requires caloric restriction at each meal. That being said, the more restrictive protocols can present a considerable challenge to some. When paired with resistance exercise, there doesn’t seem to be strength or muscle losses, but further research is required.
Most of the purported benefits of fasting come from the shift into an energy-scarce state, which upregulates metabolic pathways associated with cell-cycle regulation and energy mobilization. Shorter fasts probably don’t provoke these changes, but fasting for 18 hours or more might. Although there isn’t a lot of data on extended fasts, one 24-hour fasting study saw considerable improvements in blood pressure and glycemic control.
For some people, these protocols may be easier to follow than standard weight loss diets. Additionally, they may lead to cardiometabolic benefits.
No studies have specifically investigated the safety of these protocols, but most studies report a small number of adverse effects that typically include hunger, headaches, slight dizziness, or gastrointestinal upset.
Following these protocols, especially OMAD, can be quite difficult for some. Studies have reported high rates of participant dropout, likely due to the challenge of adhering to such a limited eating window on a sustained basis.
For those who are looking to optimize muscle growth, long fasting periods may not be ideal, but this isn’t completely clear yet.
Finally, fasting can be contraindicated in some diseases such as type 1 diabetes, pregnancy, and preexisting eating disorders. For individuals with these or similar conditions, speaking with a well-informed physician is warranted.
Although no serious side effects have been reported in existing studies, some individuals with medical conditions may want to exercise more caution.
- Time-restricted Eating
- Time-restricted Feeding
- The Warrior Diet
How to follow 20:4 & OMAD
Simply allocate an 18 to 23 hour window in the day during which you will abstain from calories completely. Many choose their fasting window to begin around 8 p.m. and extend to dinnertime the next day, but it’s just as possible to eat earlier in the day and stop eating earlier.
Studies using 16:8 fasting protocols have found that insulin sensitivity (and thus overall glycemic response to food) tends to be better in the morning, so having an early eating window may be preferable for some people, although many opt to eat later in the day because it’s more conducive with social eating. Adherence to these protocols is typically easier for people who have familial support, and for some the practice becomes easier with time.
Generally speaking, water, tea, seltzer, and coffee are considered permissible to eat during the fasting window. While other things such as chewing gum, exogenous ketones, MCT oil, supplements, apple cider vinegar, and artificial sweeteners are hotly debated, a good rule of thumb is that if the product has more than 5-10 kcal then it should be avoided until the fasting window ends.
It’s simple: don’t consume anything except for water, coffee, or tea for 18 to 23 continuous hours, and then eat freely for the rest of the day.
- ^Jakubowicz D, Barnea M, Wainstein J, Froy OHigh caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese womenObesity (Silver Spring).(2013 Dec)
- ^Hutchison AT, Regmi P, Manoogian ENC, Fleischer JG, Wittert GA, Panda S, Heilbronn LKTime-Restricted Feeding Improves Glucose Tolerance in Men at Risk for Type 2 Diabetes: A Randomized Crossover TrialObesity (Silver Spring).(2019 May)
- ^Garaulet M, Gómez-Abellán P, Alburquerque-Béjar JJ, Lee YC, Ordovás JM, Scheer FATiming of food intake predicts weight loss effectivenessInt J Obes (Lond).(2013 Apr)
- ^Andrew W McHill, Andrew Jk Phillips, Charles A Czeisler, Leigh Keating, Karen Yee, Laura K Barger, Marta Garaulet, Frank Ajl Scheer, Elizabeth B KlermanLater circadian timing of food intake is associated with increased body fatAm J Clin Nutr.(2017 Nov)
- ^Stephanie A Lee, Caroline Sypniewski, Benjamin A Bensadon, Christian McLaren, William T Donahoo, Kimberly T Sibille, Stephen AntonDeterminants of Adherence in Time-Restricted Feeding in Older Adults: Lessons from a Pilot StudyNutrients.(2020 Mar 24)
- ^Stote KS, Baer DJ, Spears K, Paul DR, Harris GK, Rumpler WV, Strycula P, Najjar SS, Ferrucci L, Ingram DK, Longo DL, Mattson MPA controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adultsAm J Clin Nutr.(2007 Apr)
- ^B D Horne, J B Muhlestein, D L Lappé, H T May, J F Carlquist, O Galenko, K D Brunisholz, J L AndersonRandomized cross-over trial of short-term water-only fasting: metabolic and cardiovascular consequencesNutr Metab Cardiovasc Dis.(2013 Nov)
- ^Matthew T Stratton, Grant M Tinsley, Michaela G Alesi, Garrett M Hester, Alex A Olmos, Paul R Serafini, Andrew S Modjeski, Gerald T Mangine, Kelsey King, Shelby N Savage, Austin T Webb, Trisha A VanDusseldorpFour Weeks of Time-Restricted Feeding Combined with Resistance Training Does Not Differentially Influence Measures of Body Composition, Muscle Performance, Resting Energy Expenditure, and Blood BiomarkersNutrients.(2020 Apr 17)
- ^Grant M Tinsley, M Lane Moore, Austin J Graybeal, Antonio Paoli, Youngdeok Kim, Joaquin U Gonzales, John R Harry, Trisha A VanDusseldorp, Devin N Kennedy, Megan R CruzTime-restricted feeding plus resistance training in active females: a randomized trialAm J Clin Nutr.(2019 Sep 1)
- ^Grant M Tinsley, Jeffrey S Forsse, Natalie K Butler, Antonio Paoli, Annie A Bane, Paul M La Bounty, Grant B Morgan, Peter W GrandjeanTime-restricted feeding in young men performing resistance training: A randomized controlled trialEur J Sport Sci.(2017 Mar)
- ^Maria V Deligiorgi, Charis Liapi, Dimitrios T TrafalisHow Far Are We from Prescribing Fasting as Anticancer Medicine?Int J Mol Sci.(2020 Dec 1)
- ^Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CMEarly Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with PrediabetesCell Metab.(2018 Jun 5)
- Beta-cell function - Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CMEarly Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with PrediabetesCell Metab.(2018 Jun 5)
- Weight - B D Horne, J B Muhlestein, D L Lappé, H T May, J F Carlquist, O Galenko, K D Brunisholz, J L AndersonRandomized cross-over trial of short-term water-only fasting: metabolic and cardiovascular consequencesNutr Metab Cardiovasc Dis.(2013 Nov)
- Beta-cell function - Carlson O, Martin B, Stote KS, Golden E, Maudsley S, Najjar SS, Ferrucci L, Ingram DK, Longo DL, Rumpler WV, Baer DJ, Egan J, Mattson MPImpact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and womenMetabolism.(2007 Dec)
- Weight - Stote KS, Baer DJ, Spears K, Paul DR, Harris GK, Rumpler WV, Strycula P, Najjar SS, Ferrucci L, Ingram DK, Longo DL, Mattson MPA controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adultsAm J Clin Nutr.(2007 Apr)
- Weight - Grant M Tinsley, Jeffrey S Forsse, Natalie K Butler, Antonio Paoli, Annie A Bane, Paul M La Bounty, Grant B Morgan, Peter W GrandjeanTime-restricted feeding in young men performing resistance training: A randomized controlled trialEur J Sport Sci.(2017 Mar)