The 5:2 Diet Under the Spotlight

5:2 is a popular form of intermittent fasting for people who want to lose weight. The diet first hit the headlines in 2012, and interest has remained high enough for new books and cookbooks to be published every year.

So what is it about this method that dieters seem to like so much? Does it work, is it healthy and what are the pros and cons? Read on to find out.

What is the 5:2 Diet?

Basically, on 5 days a week you eat normally and on 2 days you cut the number of calories you eat drastically. Your 2 very low calorie days are considered 'fasting' days.

In essence the 5:2 is a diet that relies on producing a calorie deficit to cause weight loss. The main difference between 5:2 and a standard type of low calorie diet is that a large deficit is achieved on 2 days a week, rather than a moderate daily deficit throughout the week. 

Here's the Rules

• On ‘fast days’ you consume only 25% of your 'normal'* calories - 500 for women and 625 for men.
• Non fast days you consume your normal amount of calories
• ‘Fast days’ should not be on consecutive days

*The majority of 5:2 guidance gives 'Normal' calories as an average of 2000 a day for women and 2,500 for men. (The underlying assumption being that this is the number of calories needed to maintain normal weight.)

It's generally recommended that you eat your ‘fast day’ calories in 2 meals:

• Breakfast (200 cals for a woman, 250 for a man) and
• Dinner (300 for a woman, 375 for a man)

However some proponents say it's a good idea to go for lunch and dinner as your 2 meals for the day - especially for people who tend to skip breakfast.

The idea being that you won't 'wake up' your hunger until lunchtime, and eating your 2 meals closer together won't leave you feeling hungry for as long.

What Should I Eat on the 5:2?

One of the main benefits of the 5:2 is that, in theory, you only have to restrict what you eat on 2 days each week.

This means that most of the guidance and recipes provided relate to fast days. Advice on what to eat tends to focus on getting as much nutritional goodness and satiety value as you can from the very low calorie allowance:

• Include foods high in protein such as lean meat, fish, eggs, tofu and Quorn. Protein can help you feel fuller for longer.
• Avoid sugary foods and other refined carbohydrates. These can make you feel hungrier because your blood sugar levels peak and dip so quickly when you eat them. Opt for low GI carbs which keep blood glucose levels stable.
• Eat plenty of vegetables and salad - most veggies provide a high volume of food for very few calories which will help to make a meal satisfying.
• To get an idea of what good fast day meals look like, check out our 5:2 diet recipes

Whist the 5:2 focusses on fast days, it's important to be aware of what, and how much, you're eating on non fast days.

Does the 5:2 Diet Work?

Ultimately 5:2 is based on achieving a calorie deficit over the course of a week.

If you achieve a deficit you will lose weight. The body will burn fat stores if it's not getting sufficient energy (calories) from food.

What's less certain is the theory that fasting on two days a week makes you not want to overeat on non-fasting days. This may not turn out to be true for some people who try the diet.

For example, if you're prone to bouts of binge or comfort eating, it would be quite easy to wipe out a calorie deficit over a day or two of eating freely.

By the same token, people who start the diet from a point where they have been steadily gaining weight could easily eat enough calories on 'normal' days to make up the shortfall.

You'll probably have the best chance of success with the diet by monitoring your food and drink on normal days, especially when you first start the diet.

You can get a idea of what's reasonable for non-fast days from wlr's 5:2 diet plan which provides daily menus for both fasting and non-fasting days.

Studies have shown that the 5:2 can be just as effective as calorie counting.

The surprising thing, for a diet that is labelled 'easy', is that drop out rates can be higher than those for a standard low calorie diet.

I'd speculate two main reasons for this:

1. Fasting days, even though they're not a total fast, are much harder than they sound
2. Weight loss is slower than expected

How Much Weight Can You Lose (and how long will it take)

People possibly associate the 5:2 with fast weight loss - the word 'fast' is often used in relation to 5:2.

Unfortunately 'fast', in this instance, does not mean quick.

If the diet is followed according to the average guidelines, the average person can expect to lose up to a pound a week. Potentially a stone in four months.

That's actually a good, sustainable, rate of loss - but it may seem slow to people who have a lot of weight to lose. Especially since expectations are likely to be high given the hype around the diet. 

Why is the Diet Popular?

As with any diet that hits the headlines, the 5:2 has its celebrity followers.

Philip Schofield followed the regime before he appeared on Dancing on Ice. Comedian Dom Joly, Coronation Street actor Ian Puleston-Davies, Jennifer Lopez, Miranda Kerr, Benedict Cumberbatch, Beyonce and Ben Affleck are all fans.

Advocates of the 5:2 diet say that by fasting on only 2 days a week you can lose weight without feeling deprived – since you can have whatever you fancy on your non fast days.

There are also various health and wellbeing benefits claimed for the diet - from feeling more energetic, to protection from diseases and greater longevity.

Unfortunately, a lot of these claims are based on anecdotal evidence - especially that of the authors of 5:2 books. Dr Mosley, the most well-known 5:2 author, quotes a lot of his personal statistics and experience, for example.

Robust evidence, such as peer reviewed studies, is thin on the ground when it comes to the potential health benefits of 5:2.

Pros of the 5:2 Diet

The 5:2 is flexible

You choose the days that you are going to fast on. So if you have a night out or special event coming up, you can plan your fast and non fast days around it.

This is an important benefit when you consider that many people fall off their diet wagon simply because life gets in the way.

That said, almost any diet that relies on calorie control for weight loss (and most do) can be implemented in a flexible way. For example, wlr encourages people to view their calorie balance in the context of a week to enable flexibility.

There are no banned foods or food groups

Most 5:2 diets are not prescriptive about what should or shouldn't be eaten, other than to generally encourage healthy, unprocessed food. Some gurus lean towards the low carb for fast days.

Like any calorie-based weight loss regime its not what you eat that's important, rather how many calories were in the portion you ate.

On non fast days you can have what you fancy

This is a departure from the traditional concept of calorie control - and one of the things that people like about 5:2.

The idea of only having to watch what you eat on two days a week makes the diet seem easier than having to be 'on it' pretty much all of the time. This won't work for everyone for the reasons stated above, but for the brutally honest and self-aware amongst us it's a major plus point.

It’s a different way of approaching weight loss

Losing weight's not easy and it can take a long period of time to get to where you want to be. If you’re feeling a little jaded or bored, 5:2 provides an opportunity to refocus and mix things up a little.

It may help with your portion control

If you’re used to big portion sizes the 5:2 diet might just help with getting them under control. Much smaller portions on your fast days could help you feel more satisfied with moderate portions on other days.

Doing 5:2 diet could help you get in the right mindset

Telling yourself you can’t eat something because you’re on a diet is a great way to bring out your inner rebel.

Given that you're only officially dieting two days a week on 5:2, the risk of rebelling against your regime is minimised. After all, you always have the fallback that nothing will be off-limits tomorrow.

And Cons

Actually there aren't many cons to the 5:2 diet. It can be an effective, healthy and sustainable way to lose weight.

Some of the claims made by advocates can be a little over the top. For example, there's no evidence that doing 5:2 affects longevity.

5:2 marketing often promotes 'no need for calorie counting' as a benefit. This is somewhat misleading as fast day calories have to be strictly controlled and non-fast days could easily prevent weight loss if there's no element of control.

Possibly the biggest con is the myth that fasting on 2 days a week, even with a small amount of food allowed, is easy. It's really quite hard to do for most of us - hence a relatively high dropout rate for the diet.

Side Effects of the 5:2

Because very few human studies and no long term studies have been done there are only anecdotal side effects that have been reported.

• Hunger
  • When you’re used to 3 square meals a day, cutting back to 2 meals and no snacks could leave you feeling hungry. That in turn may dissolve your resolve, leading you to raid the kitchen cupboards for food.
• Low energy
  • Less calories in could leave you feeling lethargic and lacking in energy.
• Cravings
  • Because you’re not eating, the chances are that that is all you’ll be thinking about – cue cravings!
• Irritability
  • Being hangry is an actual thing. Couple hunger with low energy, headaches and cravings and you’ll have hanger!
• Heartburn, bloating and constipation
  • Your stomach produces acid to help digest the food you eat. Very little food in the stomach could result in excess acid which can cause heartburn. When you do eat, your stomach is kind of taken by surprise which can result in bloating and constipation.
• Feeling cold
  • When you fast, blood flow increases to your fat stores and away from your extremities. When your blood sugar decreases it can also make you more sensitive to cold.

In regard to the risks involved with going for a 5:2 diet and eating minimal calories 2 days a week, it is unlikely to be dangerous for a normal, healthy person.

However, as with any major change in diet or exercise, you should check with your GP before you go for it.

Especially if you have diabetes, liver or kidney problems, compromised immune system etc.

Tips for the 5:2 Diet

1. On fast days, stick mostly to plants and protein. That way you’ll feel fuller for longer and get all the nutrients you need
2. Vegetables are great for you everyday but, use generous portions of veg on your fast days to help fill you up
3. Drink plenty of water. This will help stave off hunger and keep you hydrated. We get some of our water from food. Less food = less water
4. Prepare for your fast days in advance by planning what you’re going to eat. How does the saying go? Fail to prepare, prepare to fail.
5. Hot drinks during the day can help stave off the pangs of hunger. You’ll need to watch your calorie and milk intake but you could go black with your tea and coffee meaning minimal calories.
6. Avoid refined carbs on your fast day. They can make you feel hungrier because your blood sugar levels peak and dip so quickly when you eat them. Opt for complex carbs – wholegrain, leafy veg, legumes etc.
7. Miso soup and cupasoups are great on a fast day. Miso soup has around 17 cals a cup and high protein lentil cupasoup has 97
8. Make what you are eating on a fast day really, really tasty and eat it mindfully
9. Check out our 5:2 diet recipes

Bonus Tip

Remember – Immediate death is not a side effect of being a little bit hungry for 24 hours. The time will pass and what doesn’t kill us makes us stronger!