Fasting Tracker

Fasting plans · Intermediate

16:8 intermittent fasting

A 16-hour fast and an 8-hour eating window: the most popular plan, and the most studied

What is 16:8?

16:8 means 16 hours of fasting and an 8-hour eating window. It's the most popular plan, and Fasting Tracker suggests it as a starting point for many people (it's called Leangains in the app). Most people do it by skipping breakfast and eating between noon and 8 p.m., but any 8 hours that fit your day work.

Sample 16:8 schedules
Eating windowFastGood for
8:00 a.m. to 4:00 p.m.4:00 p.m. to 8:00 a.m.Early eaters; may suit your body clock best 5
10:00 a.m. to 6:00 p.m.6:00 p.m. to 10:00 a.m.A late breakfast and an early dinner
12:00 p.m. to 8:00 p.m.8:00 p.m. to 12:00 p.m.Skipping breakfast, the most common

What your body may do in 16 hours

By around 12 hours your liver's glycogen is getting low and your body turns more to fat. By 16 hours fat is a major source of energy, and your liver begins turning some of it into ketones 1. Most daily plans, such as 16:8, sit right at the start of this switch, repeating it every day without the strain of long fasts 6.

  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!

What the trials found

16:8 is the most studied daily plan, and the results are honest rather than magic. An umbrella review of 130 randomized trials found real benefits for weight, body fat, cholesterol, blood sugar and blood pressure, but most of the evidence was of low quality, from small, short studies 7.

Key study

16:8 alone didn't beat three meals a day

  • Randomized trial
  • 116 adults
  • 12 weeks

People who ate between noon and 8 p.m., without any other advice, lost no more weight than people eating three meals a day, and they lost more lean mass from their arms and legs.

Lowe et al., JAMA Intern Med 2020

The lesson isn't that 16:8 doesn't work. It's that the window works by helping you eat less, and that it works best with protein and strength training. In resistance-trained men and women, 16:8 with matched calories and protein kept muscle and strength 3,4.

What you can drink

Water, sparkling water, black coffee and plain tea are fine during the fast. Milk, sugar, juice and protein shakes break it 8,9. See what breaks a fast for the grey areas, such as diet soda and a splash of milk.

How to start

  1. If you've never fasted, spend a week on 13:11 or 14:10 first.
  2. Choose your 8 hours and keep them the same each day.
  3. Break your fast with a meal built around protein, vegetables and fibre 10.
  4. Do some strength training two or three times a week to protect your muscle 3.
  5. Expect the first week to be the hardest; hunger settles as your body learns the new rhythm 11.

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. Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med. 2020;180(11):1491-1499. doi.org/10.1001/jamainternmed.2020.4153
  3. Moro T, Tinsley G, Bianco A, et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. J Transl Med. 2016;14(1):290. doi.org/10.1186/s12967-016-1044-0
  4. Tinsley GM, Moore ML, Graybeal AJ, et al. Time-restricted feeding plus resistance training in active females: a randomized trial. Am J Clin Nutr. 2019;110(3):628-640. doi.org/10.1093/ajcn/nqz126
  5. Sutton EF, Beyl R, Early KS, 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;27(6):1212-1221.e3. doi.org/10.1016/j.cmet.2018.04.010
  6. Mattson MP, Moehl K, Ghena N, et al. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci. 2018;19(2):63-80. doi.org/10.1038/nrn.2017.156
  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. Holt SH, Miller JC, Petocz P. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. Am J Clin Nutr. 1997;66(5):1264-76. doi.org/10.1093/ajcn/66.5.1264
  9. Nilsson M, Stenberg M, Frid AH, et al. Glycemia and insulinemia in healthy subjects after lactose-equivalent meals of milk and other food proteins: the role of plasma amino acids and incretins. Am J Clin Nutr. 2004;80(5):1246-53. doi.org/10.1093/ajcn/80.5.1246
  10. 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
  11. 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
  12. 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.