How to start 16/8 intermittent fasting (beginner's guide)
Without starving on day one or quitting by week two. The step-by-step method to start 16/8 and actually make it easy.
Part of the complete guide How to start intermittent fasting and pick your protocol
What the science says16/8 intermittent fasting: how to start step by step
16/8 intermittent fasting means eating within an 8-hour window and fasting the other 16, sleep included. To start, ease in gradually (12/12, then 14/10, then 16/8) and stick to water, black coffee or unsweetened tea during the fast. In 8-12 week studies it produces modest weight loss (2-3%) with no calorie counting.
- 16/8 for 12 weeks in adults with obesity: -2.6% body weight, -341 kcal/day and -7 mmHg systolic pressure, with no calorie counting (Gabel 2018). [1]
- 4- and 6-hour windows for 8 weeks cut body weight about 3% and intake about 550 kcal/day with no calorie counting (Cienfuegos 2020). [2]
- Over 12 months, an 8-hour window without calorie counting lost 4.61 kg vs control, no different from calorie restriction (Pavlou 2023). [3]
What 16/8 fasting is
16/8 intermittent fasting means fitting all your meals into an 8-hour window and fasting the other 16 (sleep included). It does not change what you eat, it changes when. It is the most popular protocol because it is simple and sustainable.
Ease in: do not jump straight to 16/8
Mistake number one is going from eating all day to a 16-hour fast overnight. Build up in steps:
- Week 1: 12/12 fasting. Just stop snacking after dinner.
- Week 2: 14/10. Push breakfast back 1–2 hours.
- Week 3: 16/8. You are there.
That way your body adapts to using fat as fuel without the blood sugar crash of the first few days.
What breaks your fast and what does not
| Does not break it | Breaks it |
|---|---|
| Water | Anything with calories |
| Black coffee | Coffee with milk or sugar |
| Unsweetened tea | Juice, soda (even diet is debatable) |
| Sparkling water | Sugary gum, candy |
Golden rule: if it has calories, it breaks your fast.
What to expect the first few days
- Days 1–3: some hunger at your usual breakfast time. That is a habit, not a real need. It passes in 20–30 minutes.
- Days 4–7: hunger settles down. You start noticing steadier energy.
- Week 2 onward: fasting goes on autopilot. Many people stop being hungry in the morning at all.
Classic beginner mistakes
- Bingeing when the window opens. Fasting 16 hours is not a license to eat double. Eat normally.
- Obsessing over the clock. 15 hours 40 minutes is not a failure. Weekly consistency is what counts.
- Ignoring hydration. A lot of hunger is really thirst.
- Starting in the worst possible week. Do not kick off during weddings, travel or finals.
Is it safe? Who should skip it?
16/8 is safe for most healthy adults. Talk to your doctor first if you are pregnant or breastfeeding, have diabetes or take medication tied to meals, have a history of disordered eating, or are under 18. Fasting is a tool, not an obligation.
How Ayúname helps
Ayúname is a free app that makes 16/8 easy: set your window, start the timer, and the app shows you which phase your body is in hour by hour (digestion, glycogen, ketosis, autophagy). It tells you when you can eat, saves your streaks and keeps you going through week 1, which is the hardest.
A plan for you · 16:8 beginnerYour first 16:8 this week, without going hungry →
Free intermittent fasting app: phase-by-phase timer, autophagy, streaks and reminders. No ads.
Frequently asked questions
How long does it take to see results with 16/8 fasting?
Can you drink coffee during a 16/8 fast?
Which 8-hour window is best?
Does intermittent fasting slow your metabolism?
Scientific sources (4)
- Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutrition and Healthy Aging, 2018.
- Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metabolism, 2020.
- Time-Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population. Annals of Internal Medicine, 2023.
- Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine, 2019.