What is the 5:2 diet and is there evidence for trying it?

5:2 dietCC: Joe Holiday at Unsplash

As a form of intermittent fasting, the 5:2 Diet generated a lot of attention in its early years. Established in 2013 by a health journalist, the diet claims to allow you to eat whatever you want for five days a week. On the other two, you fast using strict calorie restriction. Those who promote the diet claims it’s excellent for weight loss, brain health, and reducing your risk of cardiovascular disease. So, how much evidence is there for the 5:2 diet and should you try it?

What is the 5:2 diet?

The 5:2 diet involves eating what you like for five days a week and fasting for two days a week. Fortunately, the fast isn’t a true fast, as you’re simply restricting yourself to 25% of your usual calories.

Depending on what’s normal for you, this can mean eating between 500 and 700 calories per day on the fast days. Most of the diet’s proponents recommend separating the fast days to make them easier to achieve. On the 5:2 diet, your fast days may look something like this:

  • Breakfast: 1/2 a cup of fat-free cottage cheese and a banana.
  • Lunch: Three ounces of grilled chicken topped with a cup of steamed vegetables.
  • Dinner: A cup of large boiled shrimp with a side of steamed broccoli.

Some people may find the 5:2 diet easier when they replace two meals a day with low-calorie shakes or soups.

Can you really eat whatever you want for five days a week?


This is where the diet is slightly misleading. You can’t eat what you want for five days a week on the 5:2 diet. You can eat up to your usual calorie requirements for your weight and fill the calories as you like. Arguably, this makes the diet more enjoyable than most.

Is intermittent fasting effective for weight loss?

Intermittent fasting could promote effective weight loss in a couple of ways. First, when you fast your insulin levels drop temporarily which then promotes fat burning. You may also see your Human Growth Hormone (HGH) levels rise, resulting in further fat loss and muscle formation. Your body may also release more noradrenaline, which again promotes fat loss.

According to research, the 5:2 diet is as effective as calorie counting for promoting and maintaining weight loss. For those who’d rather not calorie count five days per week, this is excellent news.

Is there any evidence to support the 5:2 diet?

Those who promote the 5:2 diet and intermittent fasting love to discuss its benefits beyond weight loss. One study from 2012 found that it can reduce your risk of obesity-related cancers. However, it isn’t unreasonable to assume that a calorie-controlled diet would achieve the same outcome.

A small study from 1957 appears to support claims that the diet will enhance your lifespan. However, this study focused on fewer than 60 people, so we’d need something much larger to verify its results. It’s worth noting that although the study focuses on intermittent fasting, its results are applicable to the 5:2 diet because of this.

According to this article from Johns Hopkins Medicine, eating too much is akin to rusting your brain cells. In contrast, fasting for two days a week comes with neuroprotective benefits. It specifically states that reducing your calories won’t have the same effect, making the fasting component crucial.

Could the 5:2 diet prove harmful?

Like all weight loss plans, the 5:2 diet comes with risks. If you’re diabetic and you rely on insulin, do not proceed with fasting unless your doctor helps you adjust your insulin sliding scales. As for everyone else, you may find that dizziness, dehydration, and headaches become a problem. However, some people find they can overcome this by drinking herbal teas throughout the day.

Overall, the 5:2 diet is certainly effective for weight loss. There’s limited evidence to support its other claims, but the studies that do exist look promising.

About the Author

Laura McKeever
Laura has been a freelance medical writer for eight years. With a BSc in Medical Sciences and an MSc in Physician Assistant Studies, she complements her passion for medical news with real-life experiences. Laura’s most significant experience included writing for international pharmaceutical brands, including GSK.