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.
British journalist Michael Mosley popularized it.
It’s called the 5:2 diet because five days a 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 eating method easier to stick to than a traditional calorie-restricted diet.
This article explains everything you need to know about the 5:2 diet.
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How to do the 5:2 diet
The 5:2 diet is 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 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, you probably won’t lose any weight and may even gain weight.
You should eat the same amount of food as if you hadn’t been fasting.
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.
Health benefits of intermittent fasting
There are very few studies on the 5:2 diet specifically.
However, there are plenty of studies on intermittent fasting in general, which show impressive health benefits.
One important benefit is that intermittent fasting seems easier to follow than continuous calorie restriction, at least for some people.
Also, many studies have shown that different types of intermittent fasting may significantly reduce insulin levels.
One study showed that the 5:2 diet caused weight loss similar to regular calorie restriction. Additionally, the diet effectively reduced insulin levels and improved insulin sensitivity.
Several studies have looked into the health effects of modified alternate-day fasting, which is very similar to the 5:2 diet (ultimately, it’s a 4:3 diet).
The 4:3 diet may help reduce insulin resistance, asthma, seasonal allergies, heart arrhythmias, menopausal hot flashes, and more.
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.
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.
How to eat on fasting days
There is no rule for what or when to eat on fasting days.
Suggested read: Intermittent fasting for women: A beginner's guide
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.
Focus on nutritious, high-fiber, high-protein foods that make you feel full without consuming too many calories.
Soups are a great option on fast days. Studies have shown that they may make you feel more full than the same ingredients in original form or foods with the same calorie content.
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.
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.
What to do if you feel unwell or uncontrollably hungry
During the first few fast days, you can expect overwhelming hunger episodes. 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.
Suggested read: How to fast safely: 10 helpful tips
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 feel 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; some people cannot 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 stop the diet.
Who should avoid the 5:2 diet or intermittent fasting overall?
Although intermittent fasting is 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.
Furthermore, intermittent fasting may not be as beneficial for some women as it is for men.
Some women have reported that their menstrual period stopped 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.
The 5:2 diet is an easy, effective way to lose weight and improve metabolic health.
Many people find it much easier to stick to than a conventional calorie-restricted diet.
If you’re looking to lose weight or improve your health, the 5:2 diet is definitely something to consider.