13:11 intermittent fasting

What is 13:11?

13:11 means 13 hours of fasting and an 11-hour eating window. In Fasting Tracker it's called Circadian, because it lines up with your body clock: you stop eating in the evening and start again the next morning, a little later than usual. Most of the fast happens while you sleep.

It sounds modest, but it's a real change for most people. When researchers asked healthy adults to log everything they ate with a phone app, half of them ate across more than 14 hours and 45 minutes a day, and more than a third of their calories came after 6 p.m. ¹.

Eating window	Fast	Good for
7:00 a.m. to 6:00 p.m.	6:00 p.m. to 7:00 a.m.	Early risers and early dinners
8:00 a.m. to 7:00 p.m.	7:00 p.m. to 8:00 a.m.	A usual working day
9:00 a.m. to 8:00 p.m.	8:00 p.m. to 9:00 a.m.	Later evenings

What your body may do in 13 hours

After your last meal, your body runs on the glucose from your food. A few hours later, insulin falls and your liver keeps your blood sugar steady from its glycogen and from new glucose ³. Around 12 hours, that glycogen is getting low and your body starts turning more to fat, the beginning of what researchers call the metabolic switch ². These hours are typical averages, not a schedule.

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.

Is 13:11 worth it?

No trial has tested 13:11 on its own. The closest evidence is for shortening a long eating day: when people with overweight who usually ate over 14 hours cut that to 10 or 11 hours for 16 weeks, they lost weight, said they had more energy and slept better ¹. It was a small pilot study, but it shows how much room most of us have. Finishing earlier in the evening may also suit your body clock, which handles glucose best in the morning and around midday ⁴.

How to start

Sources

1. Gill S, Panda S. A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans that Can Be Modulated for Health Benefits. Cell Metab. 2015;22(5):789-98. doi.org/10.1016/j.cmet.2015.09.005
2. 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
3. Rothman DL, Magnusson I, Katz LD, et al. Quantitation of hepatic glycogenolysis and gluconeogenesis in fasting humans with 13C NMR. Science. 1991;254(5031):573-6. doi.org/10.1126/science.1948033
4. Poggiogalle E, Jamshed H, Peterson CM. Circadian regulation of glucose, lipid, and energy metabolism in humans. Metabolism. 2018;84:11-27. doi.org/10.1016/j.metabol.2017.11.017
5. Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. doi.org/10.3390/nu11040873