What happens after 14 hours of fasting?

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.

What's happening in your body

For the first hours after your last meal, your body ran on glucose from your food. As insulin fell, your liver kept your blood sugar steady, first from its stored glycogen and more and more by making new glucose ². By 14 hours, insulin has been low for a while and the brake on your fat cells is coming off. Fat is a growing share of your fuel; ketones come later, as the fast goes on ¹.

Stage	Fuel Switch (12 to 16 h)
Main fuel	Glycogen, then more and more fat
Insulin	Low

The next stage, Fat Burning, begins around 16 hours. A 14-hour fast ends two hours before it, which is where the 14:10 plan finishes every day.

How you might feel

Hunger may peak around your usual mealtimes, and some people feel a little low on energy while the switch happens. If 14 hours ends mid-morning, the hunger you feel before breakfast is mostly habit: your hunger hormone rises before the meals you're used to and falls again on its own ^3,4.

Is a 14-hour fast worth it?

Fourteen hours sounds modest, but for most people it's a real change. When researchers asked healthy adults to log everything they ate, half of them ate across more than 14 hours and 45 minutes a day ⁵. A 14-hour fast shortens that day to 10 hours.

That 10-hour window has been tested. In 19 people with metabolic syndrome, eating within a consistent 10-hour window for 12 weeks reduced weight, blood pressure and harmful blood fats, alongside their usual medication ⁶. It was a small study without a control group, so it's a promising sign, not proof.

MYTH

Nothing happens until you've fasted for 16 hours.

FACT

The metabolic switch typically begins around 12 hours, and fat burning ramps up gradually as insulin falls ¹. Sixteen hours isn't a magic line: a 14-hour fast already spends a couple of hours in the switch, every day.

Making 14 hours a habit

14:10 is free in Fasting Tracker, called Gentle Start. See the 14:10 plan for sample schedules.

Sources

1. 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
2. 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
3. Cummings DE, Purnell JQ, Frayo RS, et al. A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans. Diabetes. 2001;50(8):1714-9. doi.org/10.2337/diabetes.50.8.1714
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. 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
6. Wilkinson MJ, Manoogian ENC, Zadourian A, et al. Ten-Hour Time-Restricted Eating Reduces Weight, Blood Pressure, and Atherogenic Lipids in Patients with Metabolic Syndrome. Cell Metab. 2020;31(1):92-104.e5. doi.org/10.1016/j.cmet.2019.11.004
7. Leidy HJ, Clifton PM, Astrup A, et al. The role of protein in weight loss and maintenance. Am J Clin Nutr. 2015;101(6):1320S-1329S. doi.org/10.3945/ajcn.114.084038