Fasting Tracker

Quick answers

How to start intermittent fasting

A step-by-step plan for beginners, from your first overnight fast to a habit that lasts

Step 1: Pick a plan

Good first plans
PlanFastExampleWhen
13:1113 hours7:00 p.m. to 8:00 a.m.Your first week
14:1014 hours7:00 p.m. to 9:00 a.m.Once 13 hours feels easy
16:816 hours8:00 p.m. to 12:00 p.m.After a comfortable week or two

Half of the adults in one study ate across more than 14 hours and 45 minutes a day 2, so even 13:11 is a real change. A fasting window helps mainly by making it easier to eat a little less without counting, so the plan you can keep is the one that works 3,4.

Step 2: Choose your hours

Pick times that fit your mornings and evenings, and keep them the same every day, weekends included. If you can, end your window in the early evening: your body handles food best in the morning and around midday 5. The fasting calculator shows when you can eat.

Step 3: Know what's normal in the first week

  • Days 1 to 2: hunger arrives at your old meal times, in waves, and fades even if you don't eat 1.
  • Days 2 to 4: maybe a headache or low energy, often from missing your usual coffee or drinking too little 6.
  • Days 4 to 7: hunger starts to even out as your hunger hormones follow the new rhythm 7.
  • Week 2 onwards: in an 8-week trial, people felt no hungrier than at the start, and fuller after meals 8.

Caffeine plays a bigger role than most people expect. In a study of 755 coffee and tea drinkers on the first day of Ramadan, when they couldn't drink during daylight, more than half got a caffeine-withdrawal headache, more often the more caffeine they usually had 9. Black coffee and plain tea don't break your fast, so keep your morning cup. More in headache while fasting.

Step 4: Drink the right things

Water, sparkling water, black coffee and plain tea are fine during the fast. Sugar, juice, milky drinks and protein shakes end it, because they raise insulin 10,11. See what breaks a fast for the grey areas.

Step 5: Break your fast with a real meal

Build your first meal around protein and vegetables, so it carries you to your next fast: protein helps you feel full 12. For ideas, see what to eat.

Step 6: Build up slowly

Your first weeks

  1. Days 1 to 3: fast 12 to 13 hours, mostly overnight.
  2. Days 4 to 7: if it felt easy, move to 14 hours. If not, stay where you are: there's no hurry.
  3. From week 2 or 3: try 16:8 a few days a week, if you want to.
  4. Add strength training two or three times a week to protect your muscle 13.
  5. Look back at your fasts each week and notice what helped.

Key study

Twelve weeks of 16:8 didn't harm wellbeing

  • Clinical study
  • 23 adults with obesity
  • 12 weeks

People ate only within an 8-hour window every day. Reported side effects, blood counts, body image and signs of disordered eating didn't change from start to finish. It was a small study, but it's reassuring for healthy adults starting out.

Gabel et al., Appl Physiol Nutr Metab 2019

Starting in January?

New Year is a popular time to begin. Make the goal a habit rather than a number on the scale: a 13- or 14-hour fast on most days for a month is a strong start. Fasting Tracker suggests a plan from a few questions, its four starter plans are free, and your streak and 57 badges mark the milestones.

Sources

  1. 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
  2. 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
  3. Liu D, Huang Y, Huang C, et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N Engl J Med. 2022;386(16):1495-1504. doi.org/10.1056/NEJMoa2114833
  4. 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
  5. 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
  6. Torelli P, Manzoni GC. Fasting headache. Curr Pain Headache Rep. 2010;14(4):284-91. doi.org/10.1007/s11916-010-0119-5
  7. Ravussin E, Beyl RA, Poggiogalle E, et al. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans. Obesity (Silver Spring). 2019;27(8):1244-1254. doi.org/10.1002/oby.22518
  8. Hoddy KK, Gibbons C, Kroeger CM, et al. Changes in hunger and fullness in relation to gut peptides before and after 8 weeks of alternate day fasting. Clin Nutr. 2016;35(6):1380-1385. doi.org/10.1016/j.clnu.2016.03.011
  9. Magdy R, El Desouky ED, Hammad EM, et al. Prevalence, characteristics, and factors associated with caffeine-withdrawal headache during the first day of Ramadan. Headache. 2023;63(3):360-367. doi.org/10.1111/head.14483
  10. 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
  11. 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
  12. 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
  13. 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
  14. Gabel K, Hoddy KK, Varady KA. Safety of 8-h time restricted feeding in adults with obesity. Appl Physiol Nutr Metab. 2019;44(1):107-109. doi.org/10.1139/apnm-2018-0389
  15. 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.