Photo: Sasun Bughdaryan / UnsplashBEFORE YOU READ
The content is informational and does not replace medical advice. Read the full medical disclaimer.
Keto decides what you eat and intermittent fasting decides when you eat it, so the two sit together without treading on each other's toes. Plenty of people arrive at fasting without planning to: they start keto, find at some point that they are no longer hungry in the morning, and breakfast quietly disappears.
For the basics of keto, start with the guide The keto diet for beginners.
Contents
What intermittent fasting is
It is a schedule in which hours or days without food alternate with hours or days of normal eating. These are the best-known versions:
Form | How it works |
|---|---|
16:8 | 16 hours without food, you eat within 8 hours, for example 12:00–20:00 |
14:10 | 14 hours without food, you eat within 10 hours |
5:2 | you eat normally on five days and very little on two days a week |
Alternate-day | one day you eat normally, the next you fast or eat very little |
If you are just starting out, 16:8 is the easiest, since you sleep through a good chunk of it.
Why it fits with keto
Once several hours have gone by without food, the liver gradually works through its glycogen stores and the body turns to fat, making ketones as it goes. Keto does something similar, except that you get to the same place by eating very few carbohydrates.
In practice, too, if keto leaves you less hungry, a narrow eating window is much easier to stick to.
What the studies say
In a study carried out in China in 2022, 139 adults with obesity followed a lower-calorie diet for 12 months. One group ate only between 8:00 and 16:00 and the other whenever they liked; the first lost 8.0 kg and the second 6.3 kg, a difference that was not statistically significant.
Most of the weight came off because of the fewer calories; the window added little on top. Fasting helps when it gets you eating less without a struggle. If you eat for two the moment the window opens, though, you gain nothing.
How to get started
It is best to start keto first and bring in fasting once the first few weeks are behind you, so that not everything changes at once. At the beginning 12 hours without food is plenty (say from 20:00 to 8:00); from there you can work up to 14 and then 16.
While you are fasting, drink water, black coffee or tea without sugar. If you feel dizzy or get a headache, low salt and water are often to blame (the Electrolyte calculator shows how much you need).
Keep an eye on protein. With two meals instead of three, the protein you used to spread over the whole day now has to fit onto fewer plates.
A 16:8 day on keto
The eating window runs from 12:00 to 20:00 and the figures come from the food database:
Time | Meal | Net carbs | Protein |
|---|---|---|---|
12:00 | Omelette with 3 eggs (150 g), 40 g feta, 100 g spinach and 10 g olive oil | 4 g | 27 g |
16:00 | 30 g almonds | 3 g | 7 g |
19:30 | 200 g baked salmon, 200 g boiled broccoli, a salad with 100 g lettuce and 15 g olive oil | 9 g | 56 g |
Total | 16 g | 90 g |
This day comes to about 1,200 calories. If you need more, make the portions bigger or add olive oil and cheese; the Macro calculator will tell you how much suits you.
Frequently asked questions
Does coffee break a fast?
Black coffee barely does, as a 30 ml espresso has about 3 calories. Add milk and sugar and it is a different story.
Do I need to fast for keto to work?
No, keto works perfectly well with three meals a day. Only add fasting if it suits you.
Can I exercise during the fasting hours?
If you feel well, yes. Keep the intensity low at first and have a meal with protein as soon as the window opens.
Sources
- Liu et al., NEJM 2022: Calorie Restriction with or without Time-Restricted Eating in Weight Loss — 139 adults, 12 months, 8.0 vs 6.3 kg, no significant difference.
- de Cabo and Mattson, NEJM 2019: Effects of Intermittent Fasting on Health, Aging, and Disease — The forms of fasting and the body’s switch from glycogen to fat and ketones.
- Ola Keto food database — the figures for the 16:8 day.
About the author
The Ola Keto team
Texts signed “The Ola Keto team” are written and edited by the people who build the site.
Comments
Comments are members’ personal views and experiences and are not medical advice. Do not change medication or treatment without your doctor.
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