Fasting Tracker

Fasting plans · Expert

The 36-hour fast

From dinner to breakfast two days later: an occasional fast for experienced fasters only

What is a 36-hour fast?

A 36-hour fast skips a full day of meals: you finish dinner on the first evening and eat again at breakfast on the third day. Fasting Tracker calls it Monk Fast, an expert plan for experienced fasters. It isn't a daily plan, and it isn't right for everyone.

What happens in your body

As a fast passes a day, your liver turns more fat into ketones, which can become a major fuel for your brain and spare your muscles from being broken down for sugar 1,4. Growth hormone rises during longer fasts, helping release fat for fuel and protect muscle 5.

  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!
  5. 24 hKetosisFat is now your main fuel, and your liver turns more of it into ketones.
  6. 36 hAutophagyCells may start clearing out old components, a natural recycling process.

What about autophagy?

Fasting Tracker marks Autophagy at 36 hours, and many websites promise it at an exact hour. The science is less tidy. Autophagy, the way your cells recycle worn-out parts, is real, and fasting is one of its strongest natural triggers in animals 6. But in people, the evidence is still early signals measured in blood 2, and even in mice it differs between organs 3. Treat the stage as an approximate guide, not a measurement.

MYTH
Longer fasts are always better, because they mean more autophagy.
FACT
There's no evidence in people that chasing autophagy with very long fasts improves health, and long fasts carry real risks. A sustainable daily rhythm is the better bet.

What are the benefits of a 36-hour fast?

Most of the research on fasting's benefits, such as weight loss and better blood pressure, cholesterol and blood sugar, comes from trials of regular fasting over weeks or months, not from occasional 36-hour fasts 7. What a 36-hour fast does reliably is take you deeper into fasting: fat and ketones become your main fuel 1, growth hormone rises 5, and your resting metabolism rises slightly rather than slowing 8.

If your goal is weight or health, a daily plan you can keep, such as 16:8, is the better-studied choice 7.

How to do it safely

  1. Be comfortable with 24-hour fasts before trying 36.
  2. Choose quiet days without hard training, long drives or important events.
  3. Drink water through the fast, with a pinch of salt to replace the sodium you lose 9.
  4. Stand up slowly and keep activity gentle.
  5. Break the fast with a small, easy meal, such as soup, eggs or yoghurt, and return to normal meals over the next day.

Sources

  1. Cahill GF Jr. Fuel metabolism in starvation. Annu Rev Nutr. 2006;26:1-22. doi.org/10.1146/annurev.nutr.26.061505.111258
  2. Jamshed H, Beyl RA, Della Manna DL, et al. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019;11(6):1234. doi.org/10.3390/nu11061234
  3. Mizushima N, Yamamoto A, Matsui M, et al. In vivo analysis of autophagy in response to nutrient starvation using transgenic mice expressing a fluorescent autophagosome marker. Mol Biol Cell. 2004;15(3):1101-11. doi.org/10.1091/mbc.e03-09-0704
  4. Owen OE, Morgan AP, Kemp HG, et al. Brain metabolism during fasting. J Clin Invest. 1967;46(10):1589-95. doi.org/10.1172/JCI105650
  5. Ho KY, Veldhuis JD, Johnson ML, et al. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. J Clin Invest. 1988;81(4):968-75. doi.org/10.1172/JCI113450
  6. Bagherniya M, Butler AE, Barreto GE, et al. The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Res Rev. 2018;47:183-197. doi.org/10.1016/j.arr.2018.08.004
  7. Patikorn C, Roubal K, Veettil SK, et al. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. JAMA Netw Open. 2021;4(12):e2139558. doi.org/10.1001/jamanetworkopen.2021.39558
  8. Zauner C, Schneeweiss B, Kranz A, et al. Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. Am J Clin Nutr. 2000;71(6):1511-5. doi.org/10.1093/ajcn/71.6.1511
  9. Sigler MH. The mechanism of the natriuresis of fasting. J Clin Invest. 1975;55(2):377-87. doi.org/10.1172/JCI107941

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.