It is claimed to cause weight loss, improve metabolic health and perhaps even extend lifespan.
All of them can be effective, but which one fits best will depend on the individual.
Here are 6 popular ways to do intermittent fasting.
1. The 16/8 Method: Fast for 16 hours each day.
The 16/8 Method involves fasting every day for 14-15 hours for women; 16 hours for men, and restricting your daily "eating window" to 8-10 hours.
Within the eating window, you can fit in 2, 3 or more meals.
This method is also known as the Leangains protocol, and was popularized by fitness expert Martin Berkhan.
Doing this method of fasting can actually be as simple as not eating anything after dinner, and skipping breakfast.
For example, if you finish your last meal at 8 pm and then don't eat until 12 noon the next day, then you are technically fasting for 16 hours between meals.
You can drink water, coffee and other non-caloric/non-sugary beverages during the fast, and this can help reduce hunger levels.
It is very important to eat mostly healthy foods during your eating window. This won't work if you eat lots of junk food or excessive amounts of calories.
BOTTOM LINE: The 16/8 method involves daily fasts of 16 hours for men, and 14-15 hours for women. On each day, you restrict your eating to an 8-10 hour “eating window” where you can fit in 2-3 or more meals.
2. The 5:2 Diet: Fast for 2 days per week.
The 5:2 diet involves eating normally 5 days of the week, while restricting calories to 500-600 on two days of the week.
This diet is also called the Fast diet, and was popularized by British journalist and doctor Michael Mosley.
On the fasting days, it is recommended that women eat 500 calories, and men 600 calories.
For example, you might eat normally on all days except Mondays and Thursdays, where you eat two small meals (250 calories per meal for women, and 300 for men).
BOTTOM LINE: The 5:2 diet, or the Fast diet, involves eating 500-600 calories for two days of the week, but eating normally the other 5 days.
3. Eat-Stop-Eat: Do a 24-hour fast, once or twice a week.
Eat-Stop-Eat involves a 24-hour fast, either once or twice per week.
This method was popularized by fitness expert Brad Pilon, and has been quite popular for a few years.
By fasting from dinner one day, to dinner the next, this amounts to a 24-hour fast.
For example, if you finish dinner on Monday at 7 pm, and don't eat until dinner the next day at 7 pm, then you've just done a full 24-hour fast.
You can also fast from breakfast to breakfast, or lunch to lunch. The end result is the same.
Water, coffee and other non-caloric beverages are allowed during the fast, but no solid food.
If you are doing this to lose weight, then it is very important that you eat normally during the eating periods. As in, eat the same amount of food as if you hadn't been fasting at all. ( Beware of overeating! )
The problem with this method is that a full 24-hour fast can be fairly difficult for many people.
BOTTOM LINE: Eat-Stop-Eat is an intermittent fasting program with one or two 24-hour fasts per week.
4. Alternate-Day Fasting: Fast every other day.
Alternate-Day fasting means fasting every other day.
There are several different versions of this. Some of them allow about 500 calories during the fasting days.
Many of the lab studies showing health benefits of intermittent fasting used some version of this.
A full fast every other day seems rather extreme, so we do not recommend this for beginners.
With this method, you will be going to bed very hungry several times per week, which is not very pleasant and probably unsustainable in the long-term.
BOTTOM LINE:Alternate-day fasting means fasting every other day, either by not eating anything or only eating a few hundred calories.
5. The Warrior Diet: Fast during the day, eat a huge meal at night.
The Warrior Diet was popularized by fitness expert Ori Hofmekler.
It involves eating small amounts of raw fruits and vegetables during the day, then eating one huge meal at night.
Basically, you "fast" all day and "feast" at night within a 4 hour eating window.
The Warrior Diet was one of the first popular "diets" to include a form of intermittent fasting.
This diet also emphasises food choices that are quite similar to a Paleo diet- whole, unprocessed foods that resemble what they looked like in nature.
BOTTOM LINE: The Warrior Diet is about eating only small amounts of vegetables and fruits during the day, then eating one huge meal at night.
6. Spontaneous Meal Skipping: Skip meals when convenient.
You don't actually need to follow a structured intermittent fasting plan to reap some of the benefits.
Another option is to simply skip meals from time to time, when you don't feel hungry or are too busy to cook and eat.
The human body is well equipped to handle long periods of famine, let alone missing one or two meals from time to time.
So if you're really not hungry one day, skip breakfast and just eat a healthy lunch and dinner. Or if you're travelling somewhere and can't find anything you want to eat, do a short fast.
Skipping 1 or 2 meals when you feel so inclined is basically a spontaneous intermittent fast.
Just make sure to eat healthy foods at the other meals.
BOTTOM LINE: Another more "natural" way to do intermittent fasting is to simply skip 1 or 2 meals when you don't feel hungry or don't have time to eat.
Who should NOT fast?
You should not fast if you are:
- Underweight (BMI < 18.5)
- Pregnant – you need extra nutrients for your child.
- Breastfeeding – you need extra nutrients for your child.
- A child under 18 – you need extra nutrients to grow.
You can fast, but may need supervision, under these conditions: