Fasting Tracker

Fasting plans · Advanced

20:4 intermittent fasting

A 20-hour fast and a 4-hour eating window: one big meal and a snack, for experienced fasters

What is 20:4?

20:4 means 20 hours of fasting and a 4-hour eating window. Fasting Tracker calls it Warrior: one big meal and a snack within 4 hours. It's an advanced plan, best tried after 16:8 and 18:6 feel easy.

Sample 20:4 schedules
Eating windowFastGood for
12:00 p.m. to 4:00 p.m.4:00 p.m. to 12:00 p.m.A main meal at lunch
3:00 p.m. to 7:00 p.m.7:00 p.m. to 3:00 p.m.A late lunch and an early dinner
4:00 p.m. to 8:00 p.m.8:00 p.m. to 4:00 p.m.Dinner as the main meal

What the research shows

The 4-hour window has been tested against a 6-hour one. Adults with obesity on either window lost about 3% of their weight in 8 weeks compared with a control group, by eating around 550 fewer calories a day without counting anything; the 4-hour window didn't do clearly better than the 6-hour one 1. So the extra two hours of fasting buy less than you might hope, and cost more effort.

What your body may do in 20 hours

  1. 0 hBlood Sugar RisingYour body is digesting your last meal and using that energy. Insulin is elevated.
  2. 4 hBlood Sugar FallingBlood sugar settles back to normal and insulin starts to drop.
  3. 12 hFuel SwitchYour liver's glycogen is getting low, so your body starts turning to fat for fuel.
  4. 16 hFat BurningYour body starts burning stored fat for energy. Stay hydrated!

Twenty hours keeps you in Fat Burning, near the edge of Ketosis, which typically begins around 24 hours 3. Hunger comes in waves at your old meal times and passes on its own 4.

Doing 20:4 well

  1. Build up from 16:8 and 18:6.
  2. Make your main meal generous in protein: your body keeps using a large serving for hours 5.
  3. Aim for about 1.6 g of protein per kilo a day if you train 2, and do strength training.
  4. Drink water through the fast, and add a pinch of salt if you feel lightheaded 6.
  5. Shorten the fast on days when it feels wrong. Flexibility is fine.

Sources

  1. Cienfuegos S, Gabel K, Kalam F, et al. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metab. 2020;32(3):366-378.e3. doi.org/10.1016/j.cmet.2020.06.018
  2. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376-384. doi.org/10.1136/bjsports-2017-097608
  3. Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018;26(2):254-268. doi.org/10.1002/oby.22065
  4. Natalucci G, Riedl S, Gleiss A, et al. Spontaneous 24-h ghrelin secretion pattern in fasting subjects: maintenance of a meal-related pattern. Eur J Endocrinol. 2005;152(6):845-50. doi.org/10.1530/eje.1.01919
  5. Trommelen J, van Lieshout GAA, Nyakayiru J, et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med. 2023;4(12):101324. doi.org/10.1016/j.xcrm.2023.101324
  6. Sigler MH. The mechanism of the natriuresis of fasting. J Clin Invest. 1975;55(2):377-87. doi.org/10.1172/JCI107941
  7. Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. doi.org/10.3390/nu11040873

A note on health

Fasting Tracker is designed for general wellness and is not a medical device. Fasting is not right for everyone. If you are pregnant, diabetic, have a history of eating disorders or take medication, talk to your doctor first, and before any extended fast.