The Truth Behind the 5:2 Diet

Intermittent fasting is a way of eating that is typified by prolonged periods of fasting, interspersed with smaller eating windows – small time periods within a day where you consume all of your daily calories.

When I first heard about intermittent fasting, I honestly thought it was a bit of a gimmick.  Just another fad diet making news headlines, claiming to help you lose weight easily and efficiently, without any real effort.

But as this whole intermittent fasting thing grew in popularity, I started to take notice.

Droves of people were swearing by its effectiveness and a number of very reputable health sources were supporting it fully.  So, I decided to do some research, and I must admit, I was quite impressed.

The basic concepts behind intermittent fasting are built around a number of solid scientific principles. Its simple application makes it a great option for a HUGE portion of the population.  

Arguably the most confusing aspect of intermittent fasting is the fact that it can be implemented in a number of different ways, making it somewhat difficult to know where to start.

Which is where today’s topic comes into play.

The 5:2 diet is one of the most popular means of implementing intermittent fasting.  In fact, it has a heap of support within the health industry – despite being a relatively recent revelation.

Related Article: How to Eat Truly Healthily Today, Every Day and Forever

What is the 5:2 Diet?

The 5:2 diet (also commonly known as The Fast Diet) is currently one of the most popular (if not the most popular) intermittent fasting diets.

Popularized by the British doctor and journalist Michael Mosely, the 5:2 diet is characterized by performing two non-consecutive days of very low energy fasting each week, combined with five days of normal eating.

The two fasting days are meant to consist of approximately 25% of your daily energy requirements, although a recommendation of 500 calories for women and 600 calories for men is also quite typical (which works out to be close to 25% of the average individual’s daily energy requirements anyway).

5:2 Diet Schedule

While this energy can come in any way, shape, or form, a common recommendation is to consume all of your calories at dinner during your fast day.  This gives you the benefits of fasting while allowing you to eat a fairly normal meal on fast days.

So, if you were to put it all together, a week on the 5:2 diet may look a little bit like this:

  • Monday: Fast day
  • Tuesday: Normal day of eating
  • Wednesday: Normal day of eating
  • Thursday: Fast day
  • Friday: Normal day of eating
  • Saturday: Normal day of eating
  • Sunday: Normal day of eating

So looking at the above, if you were to consume all of your fast day calories at dinner time, you would cease eating on Sunday night after dinner.  Then you would consume your next meal at dinner on Monday night.

In short, you would simply be skipping both breakfast and lunch on your fasting days.

Up Next: Intermittent Fasting Schedule and Rules [Infographic]

Now, it is also important to note that eating ‘normally’ on your non-fasting days doesn’t mean you can eat anything you want (that would seriously derail any of the positive effects you receive from the fasting days).  

It merely means you eat a normal healthy diet, as you would in any other situation.

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The 5:2 Diet and Fat Loss

Arguably the biggest factor that people consider when starting a new diet is its role in assisting weight loss – or more specifically – fat loss.


And this undoubtedly is why the 5:2 diet has become so popular.

You see, when implemented correctly, intermittent fasting diets, like the 5:2 diet,  provide an extremely effective way to lose fat.


Because intermittent fasting diets do more than simply cut your weekly calorie intake to lead to general weight loss.  They also induce specific fat-loss-friendly changes in your hormones.

See, after consuming food, there is an increase in the secretion of your key energy storage hormone, insulin (which promotes the movements of fatty acids and glucose from the blood and into the body’s tissue, where they can be broken down and used for energy at a later date).  

So, for a while after you eat, every time after you eat, your body is in a state of energy storage.  During these periods, it is extremely difficult for your body to break down fats for energy.

During a fasted state, on the other hand, the amount of insulin found in the blood is low, making it much easier for your body to use fat for energy and much harder for it to store fat.  

That’s a win-win for burning off fat mass!

In addition to this fat-loss-promoting decline in insulin secretion, fasting also causes a huge spike in the secretion of human growth hormone.  

Human growth hormone is one of your key anabolic hormones.  It plays a key role in helping you metabolize fat and assists in the development of new muscle.  

Combined, these key factors allow the 5:2 diet to increase your resting metabolic rate and increase your body’s ability to break down fat for energy, while simultaneously reducing your weekly energy intake.  This is a great recipe for helping you lose fat.

The 5:2 Diet and Health

While there isn’t a huge amount of research available regarding health and the 5:2 diet, specifically, there is a host of research surrounding intermittent fasting in general.  Excitingly, the majority of the results have been extremely positive.

Fasting Improves Metabolic and Cardiovascular Health

Intermittent fasting has been linked to a reduction in resting blood sugar, blood cholesterol, blood pressure — three of the most important risk factors for both cardiovascular and metabolic disease!

Why is intermittent fasting so good at cutting away at these risk factors?  

Probably because of the drop in insulin secretion I mentioned above!

It turns out, with regular fasting, you don’t just see a drop in insulin secretion during the fasted period.  You actually have a significant reduction in resting blood insulin levels at all times.  

What’s more, research also shows intermittent fasting can also substantially increase insulin sensitivity, meaning the insulin you make works better to get your blood sugar down!  

This combination is excellent for lowering blood sugar.  And a lowered blood sugar helps reduce blood cholesterol and blood pressure levels!

Since the 5:2 diet is an intermittent fasting diet, it may have the capacity to improve health and significantly reduce your risk of metabolic disease and illness!

Downsides of the 5:2 Diet

Now, although there are many positives associated with the 5:2 diet, there are also some negatives that warrant attention.

Hunger and Mood Swings

Firstly, only consuming 500 calories on fast days can be quite a challenge at the beginning.  

A lot of people aren’t particularly comfortable with feeling hungry for long periods of time.  Many people say they experience mood swings or lack of energy when adjusting to the fasting days.  

Although this normally passes after a couple of weeks, it is still important to note that the first few fast days can be pretty uncomfortable.

Finding Food You Like for 500 Calories

Secondly, 500-600 calories is really just not a lot of food.  As a result, the fast days are pretty restrictive.  It can be difficult to find food you actually like eating that fits within the set amount of calories.

This is a challenge because having to eat food that you don’t particularly like can be pretty demotivating.  And low motivation can make it less likely you’ll stick to the diet in the long run.  

Putting effort into finding low-calorie foods you enjoy eating can help you avoid this pitfall down the road.

Loss of Menstruation

Lastly, it is important for women to know that the 5:2 diet may have negative effects on their reproductive health.  

Some, but not all, women following an intermittent fasting regime have reported a complete loss of menstruation while eating this way, presumably due to the abrupt drop in calorie intake.  

Unfortunately, the women’s menstrual cycles returned only when they resumed normal eating patterns.

This suggests that this diet may not be a great option for some women.  If you try the 5:2 diet as a menstruating woman, please keep an eye out for changes in your cycle.

Be aware that the best way to restore healthy menstrual cycles (if abnormalities arise) is to abandon the diet.

Take Home Message

Although it hasn’t actually been around all that long (particularly when compared to other diets), the 5:2 diet has experienced a rapid rise in popularity, likely because it offers a simple and effective method of implementing intermittent fasting into your lifestyle.

The 5:2 diet appears to offer an easy way to improve hormone levels, boost fat metabolism, and reduce cardiovascular risk factors. 

Therefore, this diet may be a great option for those looking to lose fat mass and protect their metabolism and cardiovascular health.

While it does have some potential downsides, the benefits of the 5:2 appear to outweigh the risks for most people.

Still have questions about the 5:2 diet that needs answering?  Let us know in the comments below, and we will get back to you ASAP.

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    • Hi, John!

      Thank you so much for reaching out with your question!

      Whether or not a 5:2-style diet is a good idea with type 2 diabetes is an excellent question. As we outline in the article, and as in shown in studies like this, intermittent fasting appears to improve glucose metabolism and insulin sensitivity, which should (at least in theory) be helpful for managing type 2 diabetes. Since managing diabetes requires maintaining even blood sugar levels, though, there is a concern that prolonged fasts could actually worsen diabetes symptoms by causing low blood sugar during the fast followed by spikes when eating is resumed.

      Unfortunately, there don’t seem to be many studies on actual patients with type 2 diabetes to see how their blood sugars respond to the 5:2 diet itself — if it helps, makes it worse, or is actually dangerous.

      There are, however, a few good studies looking at the effects of fasting by diabetics during Ramadan. This is, of course, not quite the same thing, as it is a full month of whole-day fasts and there is no inherent calorie restriction (the days’ calories are simply consumed at night), but it does offer some insight into the safety of fasting with type 2 diabetes in general.

      These studies suggest that most diabetics can safely fast for Ramadan BUT this is highly dependent on how well-controlled their diabetes is, which medications (if any) they are taking to manage their symptoms, and how well those medications are adjusted for the fasting periods. Poorly adjusted medications can lead to low blood sugar (sometimes life-threateningly low) and/or extremely high rebound blood sugars, both of which are very unsafe.

      So, though I would say the 5:2 diet with type 2 diabetes is certainly possible, it really requires medical supervision to properly adjust your medications (before and during) and monitoring your blood sugar. Based on the evidence we have, I would strongly advise against starting an intermittent fasting diet without consulting your doctor, unless your diabetes is already very well controlled without any medications (and you are not taking any other medications for any other conditions). If this is the case, you could consider trying slightly longer fasts between meals, monitoring your blood sugar and symptoms yourself, and working carefully up to full intermittent fasting (though, even in this case, speaking to your doctor is probably still not be a bad idea).

      I hope this answer was helpful!

      In Health,



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