5:2 fasting: two low days a week
5:2 does not change your meal times: you eat normally five days a week, and on two non-consecutive days you limit your intake to about 500 kcal for women and 600 kcal for men.
Plan my 5:2 fast
Before you start
Fasting is not for everyone. Tick anything that applies to you: your answers stay on this screen.
Your day over 24 hours
- Eating
- Fasting
- Sleep
- Eating
- 07:30 – 19:30
- Fasting
- 12h
- 8h of fasting while you sleep
- 4h of fasting while awake
- Last meal 3h before bed
Fasting timer
Tap when you finish your last meal: the timer keeps counting even if you close the page.
Your progress
No fasts saved yet. Start the timer after your last meal: your streak will appear here.
Your progress is saved only on this device, in your browser. Nothing is sent anywhere.
What happens while you fast
Rough markers in hours since your last meal: they vary with what you ate, how active you are and your body.
Digestion
0 to 4h
Well established
What we know
Glucose from your meal enters the blood and insulin rises to move it into cells. The body stores part of the surplus as glycogen in the liver and muscles.
What we don't know
The exact timing depends on the meal: a fatty or high-fibre dish is digested more slowly than a sugary drink.
The liver takes over
4 to 12h
Well established
What we know
Insulin comes back down. The liver releases glucose from its glycogen stores to keep blood sugar steady, and fat use gradually increases.
What we don't know
Hunger comes in waves, often at your usual meal times, rather than tracking your actual reserves.
Switching to fat
12 to 18h
Established, varies a lot
What we know
Liver glycogen has dropped a lot. The body draws more on fat and starts producing ketone bodies: mild ketosis is possible for some people.
What we don't know
Studies place the switch anywhere from 12 to 36 hours: there is no guarantee it happens at 16 hours for you.
Mild ketosis
18 to 24h
Established, varies a lot
What we know
Ketone levels keep rising but stay far lower than after several days of fasting or on a strict ketogenic diet.
What we don't know
Often-quoted benefits (mental clarity, "detox") have not been shown in humans for fasts of this length.
Extended fasting
After 24h
Mostly in animals
What we know
Beyond 24 hours, the body makes more glucose from sources other than glycogen, and ketones rise clearly.
What we don't know
Autophagy (cell "recycling") is mostly measured in animals: we do not know when it increases in humans. Fasting for more than 24 hours needs medical supervision.
Sources: Cahill 2006; Rothman et al. 1991; Anton et al. 2018; de Cabo and Mattson 2019.
Your week
A plan that fits Thai habits. Tap a day to see the suggested meals.
84 hours of fasting this week
- 07:30Small light meal
- 19:00Small light meal
- About 500-600 kcal over two small meals, plenty of vegetables and water.
Small meal ideas for low days
Women: about 500 kcalMen: about 600 kcal
- Tom jued tao hu mu sap (clear tofu and pork soup) with a little rice
- Pla nueng manao (steamed fish with lime) and vegetables
- Yum woon sen (glass noodle salad) with little sugar
- Two boiled eggs and vegetables stir-fried in little oil
- Som tam Thai with no added sugar and skinless grilled chicken
- Low-sugar fresh fruit: guava (farang), rose apple (chomphu)
Calories depend a lot on portion size: check them with the calorie calculator. Work out my calorie needs →
What can you drink while fasting?
Fasting cuts calories, not water. In the Thai climate, drinking regularly prevents many headaches and energy dips.
No problem
- Still or plain sparkling waterA glass when you wake up, then regularly.
- Black coffee, no sugarAmericano or kafae dam, without condensed milk.
- Unsweetened teaGreen, black or oolong tea, hot or iced.
- Unsweetened herbal drinksPandan leaf, lemongrass or ginger.
Keep it limited
- A splash of milk in coffeeA few calories: opinions differ, skip it for a strict fast.
- "Zero sugar" drinksNo calories, but they keep sweet cravings going.
This breaks your fast
- Milk tea, bubble tea, cha yenSugar and condensed milk.
- Sweet iced coffee, soft drinksSeveral spoonfuls of sugar per glass.
- Fruit juice, sweetened soy milkEven "natural" ones contain sugar.
Very hot or sweating a lot? A pinch of salt in your water or sugar-free electrolytes can help. Dizzy or unwell: eat and drink, the fast can wait.
Work out how much water to drink →Share my plan
This tool gives general guidance and does not replace medical advice. See a doctor or dietitian before fasting if you have a health condition or take medication.
Who is it for?
It suits healthy adults who would rather have two lighter days than change their schedule every day. It is not advised during pregnancy or breastfeeding, with treated diabetes (risk of low blood sugar), with an eating disorder or under 18.
A sample day
On the five normal days, keep a 12-hour overnight fast, for example from 19:30 to 07:30. On the two low days, have two small meals around 07:30 and 19:00, for about 500 kcal (women) or 600 kcal (men).
Tips
Pick two quiet days that are not back to back, for example Monday and Thursday, avoiding festivals and family meals. Split your intake into two small meals rich in vegetables and protein, and drink plenty of water. In the study by Harvie et al. (2011), two low days a week led to as much weight loss as continuous calorie reduction.
These tools give general information. They do not replace the advice of a doctor or a qualified professional.
Frequently asked questions
- What can I eat on a 500 kcal day?
- Two small meals rich in vegetables and protein: for example a clear tofu soup with a little rice, and steamed fish with lime and vegetables. Check portions with a calorie calculator.
- Can I do the two days in a row?
- It is not advised: published protocols space the two days out so your body can recover in between.
- 5:2 or 16/8: which should I choose?
- 5:2 suits you if you would rather keep your usual meal times; 16/8 if you prefer the same rhythm every day. Both gave similar results in studies at the same intake.