- What it is: a meal-timing pattern, not a miracle. Fat loss still comes from the calorie deficit.
- The most popular form: 16/8, a daily 8-hour eating window.
- The research: in controlled trials it did not produce more weight loss than ordinary calorie restriction.
- Protein: the daily target still has to fit in the window; three meals work better than one or two big ones.
Intermittent fasting methods: 16/8, 5:2, OMAD
| Method | How it works | Who may find it convenient | Watch out for |
|---|---|---|---|
| 16/8 | 16 hours fasting daily, an 8-hour eating window (e.g. 12 to 8 pm) | People who are not hungry in the morning and like a daily rhythm. | Protein needs to be spread over 2-3 meals. |
| 14/10 | 14 hours fasting, a 10-hour window | Beginners: you simply extend the overnight break a little. | The easiest to keep; you still have to keep calories in check. |
| 5:2 | eat normally 5 days a week, about 500-600 kcal on 2 non-consecutive days | People who find a few strict days easier than daily restriction. | Fast days can bring weakness and low mood; do not schedule training on them. |
| Alternate-day fasting | one day normal eating, the next very little or nothing | Few people can keep it up for long. | Dropout was higher in one trial. |
| OMAD (one meal a day) | about 23 hours fasting, a single large meal | At most briefly and with experience. | Protein and nutrient targets are hard to hit; we do not recommend it. |
What does the research show about intermittent fasting?
The best intermittent fasting trials conclude that at the same calories it does not produce more weight loss than ordinary calorie restriction:
- Alternate-day fasting (Trepanowski, 2017): a year-long trial in healthy adults with obesity. Alternate-day fasting did not produce more weight loss than daily calorie restriction, and more people dropped out.
- 16/8 (Lowe, 2020): a 12-week trial. The 16/8 group did not lose significantly more than people who ate at their usual times.
- Calorie restriction with fasting (Liu, 2022): a year-long trial. An 8-hour eating window added nothing beyond calorie restriction.
That does not mean it does not work: if an eating window helps you eat less, it is a good tool. It is just not a metabolic trick. There is less direct evidence on 5:2; the principle is the same.
Protein in the eating window
According to the ISSN, 0.25 g/kg or 20-40 g of protein per meal is the dose that best kick-starts muscle protein synthesis. During fat loss the target is 1.8-2.4 g/kg a day. With few meals, each serving gets very large:
| Body weight | Daily protein | 3 meals | 2 meals | 1 meal (OMAD) |
|---|---|---|---|---|
| 60 kg | 108 g | 36 g | 54 g | 108 g |
| 70 kg | 126 g | 42 g | 63 g | 126 g |
| 80 kg | 144 g | 48 g | 72 g | 144 g |
| 90 kg | 162 g | 54 g | 81 g | 162 g |
In a 16/8 window it works better with three meals than with two big ones; OMAD crams the whole day’s protein into one meal, which is rarely achievable. The protein calculator works out your own number.
A sample 16/8 day built from our recipes
Eating window: 12:00 to 20:00. The day comes to 1,384 kcal and 133 g of protein over three meals. If your calorie target is higher, add a shake (for example Chocolate Peanut Butter Shake: 405 kcal, 39 g of protein), which takes it to 1,789 kcal and 172 g.
| Time | Meal | kcal | Protein (g) |
|---|---|---|---|
| 12:00 | Teriyaki Chicken Bowl | 528 | 48 |
| 15:30 | Greek Yogurt Protein Bowl | 352 | 41 |
| 19:30 | Chicken & Broccoli Stir-Fry | 504 | 44 |
| Total | 1,384 | 133 |
During the fast, water, unsweetened tea and black coffee are fine. We cover the limits for caffeine on our supplements page. Make the first meal protein-rich, and do not eat the whole day’s food at once.
Who should not do intermittent fasting?
Fit fasting around training: if you train, plan a meal for after the session. With a headache, dizziness or lasting weakness, eat, and talk to a doctor. Fasting is not the only route: if three or four meals make the deficit easier, that is just as good. The general steps are on the weight loss page.
Frequently asked questions
What is intermittent fasting?
An eating pattern that alternates hours of eating and fasting. The most common are 16/8 (16 hours fasting, 8 hours eating), 5:2 (two low-calorie days a week) and alternate-day fasting.
What is the 16/8 diet?
You do not eat for 16 hours a day and eat within the remaining 8, for example from 12 to 8 pm. Outside the window, calorie-free drinks (water, tea, black coffee) are fine.
Does intermittent fasting work better than 3-5 meals a day?
According to controlled trials, no, when calories are equal. If an eating window helps you eat less it is a good tool, but it is not a metabolic trick.
How much protein do I need in the eating window?
The same as without fasting: 1.8-2.4 g/kg a day while losing fat. 20-40 g per meal is the effective dose, so in a 16/8 window three meals beat two.
Can I train while fasting?
Yes, but plan a protein-rich meal for after the session. On the fast days of 5:2 training is hard, so rest instead.
What can I drink while fasting?
Water, unsweetened tea and black coffee. Sweetened drinks and coffee with milk break the fast.
Who should not do intermittent fasting?
Not without medical advice if you are pregnant or breastfeeding, under 18, have or struggle with an eating disorder, are treated with insulin or diabetes medication, are underweight, or are older and frail.
Sources
- Trepanowski JF et al. Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults: a randomized clinical trial. JAMA Intern Med 2017;177:930-8
- Lowe DA 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;180:1491-9
- Liu D et al. Calorie restriction with or without time-restricted eating in weight loss. N Engl J Med 2022;386:1495-504
- Jäger R et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20
- EFSA: Scientific opinion on the safety of caffeine. EFSA Journal 2015;13(5):4102