Intermittent fasting is an eating pattern that involves regular fasting.
The 5:2 diet, also known as The Fast Diet, is currently the most popular intermittent fasting diet.
It was popularized by British journalist Michael Mosley.
It's called the 5:2 diet because five days of the week are normal eating days, while the other two restrict calories to 500–600 per day.
Because there are no requirements about which foods to eat but rather when you should eat them, this diet is more of a lifestyle.
Many people find this way of eating to be easier to stick to than a traditional calorie-restricted diet (1).
This article explains everything you need to know about the 5:2 diet.
The 5:2 diet is actually very simple to explain.
For five days per week, you eat normally and don’t have to think about restricting calories.
Then, on the other two days, you reduce your calorie intake to a quarter of your daily needs. This is about 500 calories per day for women, and 600 for men.
You can choose whichever two days of the week you prefer, as long as there is at least one non-fasting day in between them.
One common way of planning the week is to fast on Mondays and Thursdays, with two or three small meals, then eat normally for the rest of the week.
It's important to emphasize that eating "normally" does not mean you can eat anything. If you binge on junk food, then you probably won't lose any weight, and you may even gain weight.
You should eat the same amount of food as if you hadn't been fasting at all.
Summary The 5:2 diet involves eating normally for five days per week, then restricting your calorie intake to 500–600 calories on the other two days.
There are very few studies on the 5:2 diet specifically.
One study showed that the 5:2 diet caused weight loss similar to regular calorie restriction. Additionally, the diet was very effective at reducing insulin levels and improving insulin sensitivity (8).
One randomized controlled study in both normal-weight and overweight individuals showed major improvements in the group doing 4:3 fasting, compared to the control group that ate normally (12).
After 12 weeks, the fasting group had:
- Reduced body weight by more than 11 pounds (5 kg).
- Reduced fat mass by 7.7 pounds (3.5 kg), with no change in muscle mass.
- Reduced blood levels of triglycerides by 20%.
- Increased LDL particle size, which is a good thing.
- Reduced levels of CRP, an important marker of inflammation.
- Decreased levels of leptin by up to 40%.
Summary The 5:2 diet may have several impressive health benefits, including weight loss, reduced insulin resistance and decreased inflammation. It may also improve blood lipids.
If you need to lose weight, the 5:2 diet can be very effective when done right.
This is mainly because the 5:2 eating pattern helps you consume fewer calories.
Therefore, it is very important not to compensate for the fasting days by eating much more on the non-fasting days.
That said, fasting protocols similar to the 5:2 diet have shown a lot of promise in weight loss studies:
- A recent review found that modified alternate-day fasting led to weight loss of 3–8% over the course of 3–24 weeks (15).
- In the same study, participants lost 4–7% of their waist circumference, meaning that they lost a lot of harmful belly fat.
- Intermittent fasting causes a much smaller reduction in muscle mass when compared to weight loss with conventional calorie restriction (15, 16).
Intermittent fasting is even more effective when combined with exercise, such as endurance or strength training (17).
Summary The 5:2 diet should be very effective for weight loss if done correctly. It may help reduce belly fat, as well as help maintain muscle mass during weight loss.
There is no rule for what or when to eat on fasting days.
Some people function best by beginning the day with a small breakfast, while others find it best to start eating as late as possible.
Generally, there are two meal patterns that people follow:
- Three small meals: Usually breakfast, lunch and dinner.
- Two slightly bigger meals: Only lunch and dinner.
Since calorie intake is limited — 500 calories for women and 600 calories for men — it makes sense to use your calorie budget wisely.
Here are a few examples of foods that may be suitable for fast days:
- A generous portion of vegetables
- Natural yogurt with berries
- Boiled or baked eggs.
- Grilled fish or lean meat
- Cauliflower rice
- Soups (for example miso, tomato, cauliflower or vegetable)
- Low-calorie cup soups
- Black coffee
- Still or sparkling water
There is no specific, correct way to eat on fasting days. You have to experiment and figure out what works best for you.
Delicious Low-Calorie Meals
There are plenty of websites with delicious meal plans and recipes for the 5:2 diet.
- Check out this site for plenty of low-calorie meal ideas.
- This site offers ideas for 10 fasting days that are worth checking out.
- Here are 27 meal plans for 500-calorie fast days.
- You can find all kinds of information and recipes on the chat forum of the official Fast Diet website.
- There are also several books and cookbooks available for the 5:2 diet, including the best-selling book called The Fast Diet.
Summary There are many meal plans and recipes available on the Internet for 500–600 calorie fast days. Sticking to nutritious, high-fiber and high-protein foods is a good idea.
During the first few fast days, you can expect to have episodes of overwhelming hunger. It is also normal to feel a little weaker or slower than usual.
However, you'll be surprised at how quickly the hunger fades, especially if you try to keep busy with work or other errands.
Additionally, most people find that the fast days become easier after the first few fasts.
If you are not used to fasting, it may be a good idea to keep a small snack handy during your first few fasts, just in case you feel faint or ill.
But if you repeatedly find yourself feeling ill or faint during fast days, have something to eat and talk with your doctor about whether you should continue.
Intermittent fasting is not for everyone, and some people are unable to tolerate it.
Summary It is normal to be hungry or feel a little weaker during the first few fasts. If you repeatedly feel faint or ill, you should probably stop the diet.
Although intermittent fasting is very safe for healthy, well-nourished people, it does not suit everyone.
Some people should avoid dietary restrictions and fasting completely. These include:
- Individuals with a history of eating disorders.
- Individuals who often experience drops in blood sugar levels.
- Pregnant women, nursing mothers, teenagers, children and individuals with type 1 diabetes.
- People who are malnourished, underweight or have known nutrient deficiencies.
- Women who are trying to conceive or have fertility issues.
Some women have reported that their menstrual period stopped while they were following this type of eating pattern. However, things went back to normal when they returned to a regular diet.
Therefore, women should be careful when starting any form of intermittent fasting, and stop doing it immediately if any adverse effects occur.