Alternate-day fasting: fasting every other day works. So does eating a bit less, minus the misery.
Half your days are fasting days. It's intermittent fasting on hard mode, and it has been tested properly. The verdict: same weight loss as a normal diet, more people quit.
The short version
- What it is
- Fast (or eat about 500 calories) one day, eat normally the next. Repeat.
- Good for
- Weight loss on par with ordinary dieting. People who like hard rules.
- Bad at
- Being kept up. Higher dropout than a normal diet in the biggest trial.
- Evidence
- Moderate. Decent trials, unexciting results.
- Our take
- Too hard to live with for most people. Not part of our plan.
What alternate-day fasting actually is
Alternate-day fasting (ADF) means exactly what it says. Monday: fast. Tuesday: eat. Wednesday: fast. And so on, every week, for as long as you can stand it.
There are two versions. Strict ADF means zero calories on fast days: water, black coffee, plain tea. Modified ADF allows about 500 calories, or about a quarter of your usual intake, on fast days, often as one small meal at lunch. Plenty of studies use the modified version, because most humans prefer not to faint.
It's the more intense sibling of the 5:2 diet, which only has two fast days a week, and of Eat-Stop-Eat, which has one or two.
How it works in your body
On fast days your body runs down its sugar stores and shifts towards burning fat. Insulin stays low. On feast days you refill. Over a week, half the days are very low, so your total calories drop a lot unless you overeat on the other days.
In practice, people do eat a bit more on feast days, but not enough to make up for the fast. In an Austrian study of healthy, non-obese adults, four weeks of strict ADF cut total calories by about 37% and body weight by about 4.5%.2 That's a big calorie cut. It also means you're running on empty half the time.
What you eat, what you don't
Eat
- Fast days: water, black coffee, plain tea; or one small meal of protein and vegetables
- Feast days: real food, protein at every meal
- Vegetables, legumes, whole grains, olive oil, nuts
- Eggs, fish, chicken, tofu, Greek yoghurt
- Whole fruit with meals
Forget it
- Feast days as all-you-can-eat buffets
- Sugar, soft drinks, juice
- Sweeteners and "zero" drinks on fast days
- Hard training sessions on fast days
- Ultra-processed "diet" snacks to get through the fast
A week on alternate-day fasting
Here's what modified ADF looks like when you actually live it, not when you read about it on a Sunday night full of good intentions.
- Monday (fast): black coffee, water. Lunch around 500 calories: two eggs, a big salad with olive oil, a bowl of vegetable soup. Then nothing until Tuesday.
- Tuesday (feast): normal breakfast, lunch and dinner, protein at each one. Not a revenge brunch.
- Wednesday (fast): same as Monday. This is the day most people discover how many office birthdays there are.
- Thursday (feast): normal meals. Train hard today, not yesterday.
- Friday (fast): the hardest one, because the weekend is right there.
- Saturday (feast), Sunday (fast): and because a week has seven days, next week your fast days move. That's the part that breaks most people's calendars.
In Singapore
Hawker food makes a 500-calorie fast-day lunch tricky but doable: sliced fish soup without noodles, or yong tau foo with vegetables and tofu in clear soup, skipping the fried items. On feast days, chicken rice or nasi lemak are fine as one meal, not as a "I earned it" double portion. Teh and kopi without sugar or condensed milk on fast days.
In Austria, Germany and Switzerland
Fast-day lunch: a Gemüsesuppe, a couple of eggs or a small tub of Hüttenkäse with vegetables. The traps are social: the Mittagsmenü with colleagues, Kaffee und Kuchen on a Sunday, and the Stammtisch beer that always seems to land on a fast day.
Alcohol on alternate-day fasting
OK, now and then
- One glass of dry wine with dinner on a feast day
- Spirits with soda water and lime, with food
- A light beer with a meal
Out
- Any alcohol on a fast day
- Drinking on an empty stomach at the start of a feast day
- Cocktails, liqueurs, sweet wine, beer by the litre
50 Club: one drink with dinner on a feast day, after food. Never on the evening a fast starts.
While your liver deals with alcohol, fat burning pauses: two drinks cut it by about 73% in one small study.5 Never drink while fasting or on an empty stomach. All the details are in our alcohol guide.
What alternate-day fasting is good for, with proof
Weight loss, same as a regular diet
The biggest test so far: 100 adults with obesity in Chicago, one year, ADF versus a daily calorie cut versus no diet. Both diets did about the same. Compared with the no-diet group, ADF people were 6.0% lighter after a year, the daily-diet people 5.3%.1 Not a meaningful difference. The 2026 Cochrane review agrees: intermittent fasting overall did about as well as regular diet advice.3
Markers looked better in healthy people
In the Austrian study of healthy, non-obese adults, four weeks of ADF lowered blood pressure and heart rate and improved the fat-to-muscle ratio. A separate group who had done ADF for more than six months had lower LDL cholesterol and no reported side effects.2 Interesting, but short and small, and the long-term group chose ADF themselves, so they may differ in other ways.
The uncomfortable truth
"ADF is the most powerful form of fasting." Power you can't keep up isn't power. In the year-long trial, 38% of the ADF group dropped out, compared with 29% on a daily diet.1 LDL ("bad") cholesterol also ended up higher in the ADF group after a year.1
So: ADF is not dangerous for most healthy adults and it does cause weight loss. But "the same result with more suffering" is not a great sales pitch.
The risks
- Dropout. The biggest risk is that it simply doesn't last.1 A diet you quit doesn't work.
- Cholesterol. LDL was higher with ADF than with a daily diet after a year.1 Get it checked if you do this long term.
- Diabetes medication. Fasting days roughly doubled hypos in a type 2 diabetes trial, even with lower doses.4 ADF means a fast day every other day. Don't even think about it without your doctor.
- Binge eating. Intermittent fasting has been linked with eating-disorder behaviours, including binge eating.6
- Muscle and protein. Half your days with little or no protein makes keeping muscle harder. Protein on feast days matters even more.
- Social life. Every other dinner invitation lands on a fast day. Good luck.
Allergies: watch the staples
ADF has no fixed menu. The small fast-day meals and the protein-heavy feast days lean on these.
| Staple | Allergen (EU list of 14)7 | Swap |
|---|---|---|
| Eggs | Eggs | Chicken, tofu |
| Greek yoghurt, cottage cheese | Milk | Soy yoghurt, lentils |
| Salmon, white fish | Fish | Chicken, turkey, beans |
| Tofu, soy milk | Soy | Eggs, chickpeas |
| Nuts | Tree nuts, peanuts | Pumpkin and sunflower seeds |
| Wholegrain bread | Cereals containing gluten | Brown rice, quinoa, potatoes |
Don't do alternate-day fasting if you…
- are pregnant or breastfeeding
- are under 18
- have ever had an eating disorder
- take insulin, sulfonylureas, SGLT2 or GLP-1 drugs
- are underweight, frail or older and losing muscle
- have kidney disease or high LDL cholesterol that isn't monitored
Healthen me asks about all of these and gives you a different plan if any apply.
How we use alternate-day fasting in your plan
We don't. ADF is an info article for us. It gives the same weight loss as gentler approaches, with more dropouts. That's the opposite of what we're after: habits you keep for life.
Instead, your plan has a daily eating window (see time-restricted eating), as long as you comfortably can, and one fasting day after your weekly Rebel Day. Longer fasts belong under medical supervision, as described in extended fasting.
This article is general information, not medical advice. If you have a medical condition or take medication, talk to your doctor before changing how you eat.
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 Internal Medicine 2017;177(7):930–938. doi.org/10.1001/jamainternmed.2017.0936
- Stekovic S et al. Alternate day fasting improves physiological and molecular markers of aging in healthy, non-obese humans. Cell Metabolism 2019;30(3):462–476. doi.org/10.1016/j.cmet.2019.07.016
- Garegnani LI et al. Intermittent fasting for adults with overweight or obesity. Cochrane Database of Systematic Reviews 2026, Issue 2, CD015610. doi.org/10.1002/14651858.CD015610.pub2
- Corley BT et al. Intermittent fasting in type 2 diabetes mellitus and the risk of hypoglycaemia: a randomized controlled trial. Diabetic Medicine 2018;35(5):588–594. doi.org/10.1111/dme.13595
- Siler SQ, Neese RA, Hellerstein MK. De novo lipogenesis, lipid kinetics, and whole-body lipid balances in humans after acute alcohol consumption. American Journal of Clinical Nutrition 1999;70(5):928–936. pubmed.ncbi.nlm.nih.gov/10539756
- Ganson KT et al. Intermittent fasting: describing engagement and associations with eating disorder behaviors and psychopathology among Canadian adolescents and young adults. Eating Behaviors 2022;47:101681. doi.org/10.1016/j.eatbeh.2022.101681
- Regulation (EU) No 1169/2011 on food information to consumers, Annex II (the 14 allergens). eur-lex.europa.eu/eli/reg/2011/1169/oj