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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.

Our evidence-based analysis on omad and 20:4 intermittent fasting features 13 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
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Research Breakdown on OMAD and 20:4 Intermittent Fasting

1Non-Resistance Training

In a crossover study,[5] 12 males completed an 18:6 diet and a 12:12 diet in random order. In both treatments, participants could only eat the three meals provided to them throughout the day. This study was designed purely to test the effects of meal timing, so there was no caloric deficit in the diets. This study found that the 18:6 group had significantly improved insulin levels, ꞵ-cell function, and insulin resistance during an oral glucose tolerance test, but there were no differences in glucose levels. Additionally, systolic and diastolic blood pressure were reduced, and morning total cholesterol and triglycerides were increased. The increased triglyceride levels are suggestive of increased fat oxidation due to a longer fasting window. Finally, inflammation was not changed between groups, but levels of 8-isoprostane (a marker of oxidative stress) was significantly lower in the 18:6 group than in the control group.

In a crossover trial,[6] 21 men and women between the ages of 40 and 50 completed a standard diet and an isocaloric one-meal-a-day diet (with the meal being consumed between 4 and 8 p.m.) in random order. Each diet was eight weeks long and had no caloric deficit, and the diets were separated by an 11-week washout period. This study found that, when eating one meal a day, participants had higher systolic and diastolic blood pressure, blood urea nitrogen, albumin, liver enzymes, and total, HDL, and LDL cholesterol, and lower body weight, fat mass, cortisol, hemoglobin, red blood cell count, and hematocrit. Additionally, participants were significantly more hungry and had lower fullness when eating one meal a day. Unfortunately, this study collected their vitals and blood samples at different times of day between the groups. Because a number of these values (especially blood pressure and cortisol) are subject to variation during the day, this is a significant source of confounding.

The participants from this study also performed an oral glucose tolerance test, which was reported in a secondary analysis.[13] This study found that one meal a day significantly worsened glycemic response to an oral glucose tolerance test and higher fasting glucose compared to the standard diet. The authors noted, however, that because the oral glucose tolerance tests were performed in the morning, the one-meal-a-day group had their glycemic control assessed much closer to the time they last ate, which may have reduced their performance.

2Resistance Training

In a randomized controlled trial,[3] 28 healthy, untrained males underwent an eight-week resistance training program (with three nonconsecutive training sessions per week) plus either a normal diet or a 20:4 diet to be implemented on non-training days. The subjects were not given any instruction on what or how much to eat. This study found that, on the days they fasted, participants in the 20:4 group ate about 650 fewer calories, although their weight did not change. Additionally, the percentage of each macronutrient did not change. Finally, although strength improved in both groups, there were no differences between groups. Notably, the normal diet group did have increased lean mass compared to the 20:4 group, but this difference did not reach statistical significance.

3Single-Day Trials

In a crossover study,[12] 30 otherwise healthy individuals followed a normal day of eating and a 24-hour water-only fast, in random order, with no washout period. This study found that a day of water-only fasting increased growth hormone, hemoglobin, red blood cell count, hematocrit, and total, LDL, and HDL cholesterol, and decreased fasting glucose, fasting insulin, insulin resistance, triglycerides, bicarbonate, and body weight compared to a normal day of eating. There were no changes in blood pressure.


  1. ^ Matthew T Stratton, et al. Four Weeks of Time-Restricted Feeding Combined With Resistance Training Does Not Differentially Influence Measures of Body Composition, Muscle Performance, Resting Energy Expenditure, and Blood Biomarkers. Nutrients. (2020)
  2. ^ Grant M Tinsley, et al. Time-restricted feeding plus resistance training in active females: a randomized trial. Am J Clin Nutr. (2019)
  3. ^ a b c Tinsley GM, et al. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. Eur J Sport Sci. (2017)
  4. ^ Maria V Deligiorgi, Charis Liapi, Dimitrios T Trafalis. How Far Are We from Prescribing Fasting as Anticancer Medicine?. Int J Mol Sci. (2020)
  5. ^ a b c Sutton EF, et al. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. (2018)
  6. ^ a b c Stote KS, et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. Am J Clin Nutr. (2007)
  7. ^ Jakubowicz D, et al. High caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women. Obesity (Silver Spring). (2013)
  8. ^ Hutchison AT, et al. Time-Restricted Feeding Improves Glucose Tolerance in Men at Risk for Type 2 Diabetes: A Randomized Crossover Trial. Obesity (Silver Spring). (2019)
  9. ^ Garaulet M, et al. Timing of food intake predicts weight loss effectiveness. Int J Obes (Lond). (2013)
  10. ^ Andrew W McHill, et al. Later circadian timing of food intake is associated with increased body fat. Am J Clin Nutr. (2017)
  11. ^ Stephanie A Lee, et al. Determinants of Adherence in Time-Restricted Feeding in Older Adults: Lessons from a Pilot Study. Nutrients. (2020)
  12. ^ a b B D Horne, et al. Randomized cross-over trial of short-term water-only fasting: metabolic and cardiovascular consequences. Nutr Metab Cardiovasc Dis. (2013)
  13. ^ Carlson O, et al. Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women. Metabolism. (2007)