Intermittent fasting works for weight loss when it helps you eat fewer calories; with the same calories, studies find it about as effective as ordinary calorie counting. Keep your protein high and keep lifting so the weight you lose is fat, not muscle.
Intermittent fasting means eating in a set window of time and not eating outside it. It has become one of the most popular ways to try to lose weight. But does skipping breakfast really burn more fat?
The common types
- 16:8. You eat within an 8-hour window, for example from 12 noon to 8 pm, and fast for the other 16 hours. The most popular version.
- 14:10. A gentler start: a 10-hour eating window.
- 5:2. You eat normally five days a week and eat very little, about 500 to 600 calories, on two days that are not back to back.
- One meal a day (OMAD). A single meal, usually in the evening. Hard to keep up, and hard to get enough protein.
What the research shows
When studies compare intermittent fasting with ordinary calorie counting, with the same total calories, the weight loss is usually about the same. The fasting window itself does not burn extra fat. What it does is make it easier for some people to eat less, because there are fewer chances to eat during the day.
So intermittent fasting is a tool for eating less, not a magic switch. If the window helps you eat fewer calories without feeling worse, it works for you. If you end up eating more in your window, it does not.
The best diet is the one you can keep. Intermittent fasting is one way to eat less; it is not the only one.
Who it can suit
- People who are not hungry in the morning anyway.
- People who prefer two bigger meals over four smaller ones.
- People who snack a lot at night: a clear "kitchen closed" time helps.
- People who find counting calories every day stressful.
Who should be careful
- Anyone with diabetes, especially on insulin or tablets that lower blood sugar.
- Anyone with a history of eating disorders.
- Pregnant or breastfeeding women.
- Teenagers who are still growing.
- People on medicines that need to be taken with food.
Talk to your doctor first if any of these apply to you.
How to do it without losing muscle
The main risk of fasting is not eating enough protein, especially if you train.
- Hit your protein target in your window: around 1.6 to 2.2 g per kilogram of bodyweight a day.
- Two or three protein-rich meals inside the window, rather than one big one.
- Keep lifting weights two to four times a week.
- Train near your window if you can, so a meal follows your workout.
- Drink during the fast: water, black coffee and plain tea do not break it.
A simple way to try it
Start with 12:12, eating for example from 8 am to 8 pm. After a week, try 14:10, then 16:8 if you feel good. Keep your calories, protein and food quality the same as you would on any good plan, and watch your weekly average weight for three to four weeks.
Sources
- Time-restricted eating against calorie counting for a year: Liu et al., 2022
- A 12-week 16:8 fasting trial: Lowe et al., 2020
- Alternate-day fasting against daily calorie restriction: Trepanowski et al., 2017
The takeaway
Intermittent fasting works when, and because, it helps you eat fewer calories. It is not better than other diets, but it may be easier for you. Choose the window that fits your life, keep your protein high, and judge it by your results. Shulah's diary shows your calories and macros as you log, whatever hours you eat in.