The 5:2 Diet, which was introduced in Europe many years ago, continues to be one of the most popular variations of intermittent fasting today. Is it a solid diet that produces results, or is it just all hype?

In 2012, a new diet called the 5:2 Diet swept across the United Kingdom. It became so popular that it even spread across the channel to Europe and then to the United States.

It’s not hard to see why. The 5:2 Diet, also called the FastDiet, promotes weight loss by restricting calorie intake only twice a week.

Dieting only twice a week and eating as you normally would for the rest of the week does sound appealing. But does it work? Let’s find out.

Overview and history of the 5:2 Diet

The 5:2 Diet first came into public awareness through an episode of the documentary series Horizons on BBC Two. In this episode, entitled “Eat, Fast and Live Longer,” British journalist and medical doctor Michael Mosley described his quest for weight loss and longevity.

Dr. Mosley claimed his quest is possible through the ancient practice of fasting. He also explained the modern science proving that fasting works.

Soon after the Horizons episode, Dr. Mosley partnered with fellow journalist Mimi Spencer. Together, they pooled their knowledge and experience to write a book called The FastDiet, which further elaborated the ideas Dr. Mosley presented in the Horizons episode.

This book led to the creation of other books supporting Dr. Mosley’s theories, as well as other tools and resources for fasting and weight loss.

Main purpose and goal of the 5:2 Diet

The 5:2 Diet is essentially a close cousin of the alternate day fasting (ADF) diet. Just like ADF, 5:2 aims to help people lose weight without the stress of calorie counting and calorie restriction. It’s meant to be a simple, fuss-free way to shed off unwanted pounds.

What makes the 5:2 Diet simple and fuss-free? In 5:2, you get to have two non-consecutive fast days every week.

On those fast days, you get to limit your calorie intake to 500 calories if you’re female and 600 calories if you’re male. On regular days, which are the remaining five days of the week, you can eat as much as you want.

The 5:2 Diet is designed to be a lot less painful than ADF or any other approaches to intermittent fasting out there. Instead of fasting every other day, you get to fast only two days. You get to pick your fast days according to your schedule. The only condition is they must be non-consecutive days.

Moreover, the fast days are not really complete fasts since you still get to eat on those days. In theory, the 5:2 Diet is a lot less stressful and much easier to follow than other intermittent fasting approaches.

Who is the 5:2 Diet ideal for?

The 5:2 Diet is great for anyone who wants to lose weight and don’t have any existing pre-conditions that may prevent them from fasting. As an approach to intermittent fasting, 5:2 promotes restricting calorie intake.

However, unlike other diets that cut back calorie intake, it is much less stressful and a lot less prohibitive. It’s because you don’t have to do it every day.

For people who want to get into the intermittent fasting lifestyle, 5:2 is also a good starting point.

Fasting twice a week as required by the FastDiet can condition your body for longer and more restrictive intermittent fasting approaches like the LeanGains protocol or Ori Hofmelker’s popular Warrior Diet.

Is the 5:2 Diet easy to do?

In theory, the 5:2 Diet is extremely easy to implement. You only need to schedule two fast days every week. On those fast days, you restrict your calorie intake to 500 calories if you’re a woman and 600 calories if you’re a man. On regular days, you may eat as you normally would.

The challenge of the 5:2 Diet is coping with hunger pangs on fast days. As it is with ADF, there’s no telling when or whether your body will eventually become used to these hunger pangs.

To cope with hunger, you may drink non-caloric drinks such as water, coffee, and black tea. Just make sure your drinks don’t have any sugar in it to avoid sudden glucose or insulin spikes.

If you take milk with your coffee, the calories you’ll ingest with your milk must be taken out of your calorie allowance for the day. Lastly, you may drink diet drinks, but only in moderation.

Do you need to work out on the 5:2 Diet? You’re not really required to do so, but Dr. Mosley highly recommends complementing the diet with regular exercise.

He describes his recommended exercise protocol in the book FastExercise: The Simple Secret of High Intensity Training, which describes the benefits of ten-minute high-intensity training three times a week. However, he advises against doing strenuous workouts on fast days.

5:2 diet exercise stair running

High intensity exercises like stair running are great to pair with the 5:2 Diet.

Foods that are part of the 5:2 Diet

The 5:2 Diet does not pose any food restrictions. Just like other approaches to intermittent fasting, what this diet does is to change your eating pattern. Through this altered eating pattern, you’re expected to create the calorie deficit required to lose weight without really thinking about it.

There is only one rule to the 5:2 Diet, and that is to restrict your calorie intake on fast days. You may eat whatever you want on regular days.

However, it is strongly suggested that you still limit your eating within your recommended daily calorie intake on regular days. That’s because you really won’t experience the benefits of the 5:2 Diet if you eat without limits on regular days. This kind of feasting will not create the calorie deficit you need for weight loss.

How do you calculate the amount of calories you need to eat on non-fasting days? Dr. Mosley offers a simple online calculator on his website.

This calculator will yield your body mass index (BMI), your basal metabolic rate (BMR), and your total daily energy expenditure (TDEE). The calculator computes this by taking into consideration your sex, age, height, weight, and general level of activity.

While you can eat what you want to eat both on fasting and regular days, it’s suggested that you still watch what you eat. You should eat foods that are nutritionally dense, high in fiber, and high in protein. These foods will improve your health and well-being. They will also prevent hunger pangs on fasting days.

You may find it a challenge to apportion your limited calorie allowance on fast days. After all, how do you divide 500 or 600 calories into meals that will sustain you for the whole day?

There’s no specific way you can divide your calorie allowance on fast days. But you can divide it into three small meals (breakfast, lunch, and dinner) or two large-ish meals (breakfast and dinner or lunch and dinner only).

To help people on the 5:2 diet, Mimi Spencer, Dr. Mosley’s writing partner, published two cookbooks containing low-calorie recipes for fast days: The FastDiet Cookbook and The FastDay Cookbook.

Foods that are to be avoided on the 5:2 Diet

Again, since the 5:2 Diet does not impose any food restrictions, you don’t need to avoid specific food types on this diet. You may eat whatever you want to eat.

However, on fast days, it is highly recommended that you stay away from sugar. Sugar can cause your glucose and insulin levels to fluctuate. These fluctuations can make your hunger pangs feel worse.

Even though you may eat whatever you want on the 5:2 Diet, it’s highly recommended that you avoid eating refined and processed foods. Examples are white sugar, white rice, and canned foods. These foods have become nutrient-deficit due to processing.

Canned foods, in particular, can contain chemicals and preservatives that only add to your daily calorie count. As much as possible, you should stick to fresh and seasonal foods.

How effective is the 5:2 Diet overall?

Is the 5:2 Diet proven to be effective? Is there enough scientific literature available to back up Dr. Mosley’s weight loss method?

If you look at intermittent fasting in general, there is sufficient scientific literature backing the claim that it is an effective method for losing weight. Intermittent fasting makes weight loss possible by allowing the body access to its stored fat mainly through the depletion of glucose and liver glycogen.

Moreover, intermittent fasting stimulates the process of autophagy, in which cells repurpose their old protein molecules into new, reusable components.

In addition, research exists claiming that intermittent fasting can increase insulin sensitivity and slow down fat accumulation in the body. The research also indicates that fasting periodically can improve resistance to stress as well as longevity.

Of all the available approaches to intermittent fasting out there, the one most studied is the alternate day fast model developed by Dr. Krista Varady.

In fact, Dr. Varady’s work makes up a great portion of existing research on ADF. Her studies have proven that ADF is effective in helping people lose weight and burn off fat, whether the food eaten during feast days is high or low in fat.

Dr. Varady also did not hesitate to show that ADF is highly effective only for short-term weight loss. When it comes to longer-term weight loss, ADF is not superior to other diet systems. In contrast, a lot of weight loss gurus in the market would insist that their diet systems are sustainable for the long haul.

What about the 5:2 Diet? The 5:2 Diet is considered to be a modified version of ADF. However, unlike ADF, there is not a lot of scientific research available to back up Dr. Mosley’s claims.

There is a study, though, that shows intermittent energy restriction for two consecutive days weekly may be as effective as continuous calorie restriction. But this study was published in 2010, thus predating Dr. Mosley’s system.

So, beyond testimonial evidence, it’s hard to say whether the 5:2 Diet really works and whether its effects last on a short-term or long-term basis.

Potential mistakes to avoid on the 5:2 Diet

If you’re going to follow the 5:2 Diet, what potential mistakes should you watch out? There are two possible pitfalls that can hinder your weight loss efforts using this diet.

One pitfall is to overeat during or right after a fast day. The calorie restriction and the hunger pangs you experienced during your fast day may make you feel tempted to eat more than you should.

The 5:2 Diet will work only if you keep to your recommended calorie intake both on fast days and on regular days.

If you keep overeating, especially right after a fast day, you will only negate the work that you did during your fast day. You will not create the calorie deficit required for your weight loss.

The other pitfall is not watching what you eat on regular days. The 5:2 Diet does not have any food restrictions.

However, common sense will tell you that binge-eating on junk and high-carb foods on regular days completely negates the purpose of fasting twice a week. You can’t expect to lose weight if you don’t stick to a much healthier diet.

5:2 diet fasting sugar food cake

Avoid foods that contain sugar, such as cake, especially when fasting while on the 5:2 Diet

How healthy is the 5:2 Diet?

The 5:2 Diet is a relatively safe and healthy diet if done correctly. Aside from hunger pangs, it does not have any reported side effects.

However, the 5:2 Diet is not for everyone, just like with other intermittent fasting approaches. If you’re a woman, for instance, you should avoid intermittent fasting altogether if you’re trying to conceive.

The calorie restriction that intermittent fasting will put you through may interfere with your menstrual cycles.

If you’re pregnant, this calorie restriction may be harmful to your unborn child. If you’re breastfeeding, it may hamper your ability to produce milk for your baby.

If you have a history of eating disorders, you should also avoid intermittent fasting. Intermittent fasting may trigger your eating disorder.

If you’re sensitive to sudden fluctuations in blood sugar levels, you should also check with your doctor before beginning this diet. Otherwise, going through fast days may be dangerous for you.

Our 5:2 Diet review conclusion

The 5:2 Diet is designed to allow people to enjoy the benefits of intermittent fasting without the fuss and the stress. The idea that you’re going to restrict your calorie intake for only two days in a week does sound appealing.

But just like any other diet system, the 5:2 Diet does require some work. And other than testimonial evidence, there is only limited scientific proof that this particular intermittent fasting approach really works.

The best way to really find out if the 5:2 Diet works for your body is to learn more about it by reading The FastDiet and trying it out for yourself.