5:2 Fast Diet: A Fast Weight Loss Method

Dieting is perhaps the oldest term linked with weight loss. But fasting is a new trend.

Now fasting to lose weight does not mean starving yourself in order to lose weight. It is just a change in eating pattern.

There are many ways you can do it, but this article specifically covers 5:2 fast diet.

What is 5:2 fast diet?

5:2 fast diet has been described by Dr. Michael Mosley in his book, The Fast Diet: Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting.

It involves eating normally for 5 days a week and reducing calorie intake for 2 days.

On fasting days calorie intake should be around 600 calories for men and 500 for women which is about 25% of your normal intake. Now the catch is eating normally for 5 days.

Most people interpret it as eating whatever you want during the 5 days but that is not it. It involves no calorie counting for 5 days but at the same time doesn’t give you a free pass to eat junk food.

The 2 fast days are generally non-consecutive days and the convenient pattern is Monday and Thursday.

For example, if your last meal is on Sunday evening then you are not going to be eating normally till Tuesday morning. That would be 36 hours.

Or you can fast from Monday 2pm to Tuesday 2pm. That would be 24 hours.

How does 5:2 fast diet help in weight loss?

A quick answer would be eating less than what you require would create a calorie deficit and leads to weight loss. A short period of fasting enables your body to utilize your resources efficiently.

During the fasting period the body repairs damage that has been done and due to little carbohydrate intake it makes use of fat as a source of energy to meet your daily requirements.

What does research have to say about 5:2 diet?

Although there is a lot of hype and support for 5:2 diet, frankly there aren’t many scientific studies conducted on this pattern of eating.

Nevertheless, scientists have studied intermittent fasting in great detail and they give a thumbs up for it.

Harvie et al conducted a study comparing the effects of intermittent fasting and daily calorie restriction. Why these two techniques were compared was because dieting is rather difficult to follow.

Individuals were randomly assigned to either of the two groups:

  • Intermittent fasting: 25% of the calorie restriction 2 days a week
  • Calorie restriction: 6276 kJ/day for 7 days/week

The study lasted for 6 months. The intermittent fasting group lost around 6.4kg while the calorie restriction group lost around 5.6kg.

Both groups experienced a reduction in cholesterol, blood pressure, and insulin resistance.

Researchers concluded that Intermittent fasting is as effective as calorie restriction for weight loss.

This conclusion is also supported by other studies.

Additionally intermittent fasting also prevents loss of lean mass which might occur during dieting.

In his interview , Dr. Mark P Mattson from America's National Institute on Ageing who is testing this diet on animals shed some more light on 5:2 diet.

Coming to his own experience this is what he had to say:

‘On a Monday, I get up and I have some scrambled eggs for breakfast because the protein keeps you fuller.

That’s about 180 calories, then I skip lunch and in the evening, I have a pile of vegetables and say, a bit of fish.

That’s probably about another 300 calories.  So, the whole lot adds up to maybe 500 calories.

So, I do that Monday, Tuesday – eat normally, Wednesday normally, and on Thursday, I kind of do the same thing again.

I did that initially for 12 weeks and in the course of that, I lost around 9 kilos.

What was really good is, almost all of it was fat.  So, my body fat went down from 28% to 21%.’

It is great to know that 5:2 diet specifically targets fat and weight loss is more of fat loss.

Scientists at the University of Florida have studied the effects of a modified 5:2 diet on aging and metabolism.

Actually, this diet is more of a 4:3 diet and works on the fasting ( 25% of normal calorie intake) and feasting (175% of normal calorie intake) every alternate day.

Results showed an increase in the sirtuin gene which highly regulates aging process and a decrease in insulin levels was observed.

Overall intermittent fasting was found to be a safe weight loss tool.

Other research studies also show that alternate day fasting causes significant weight loss and lowers lipid levels.

Additional benefits with intermittent fasting include improvement in heart health, reduced risk, and improvement in metabolic disease and beneficial effects on brain health.

What does this mean? There is very little scientific evidence on 5:2 diet in particular but this technique is as effective as calorie restriction when it comes to weight loss. Additionally it positively affects metabolism and prevents loss of muscle mass.

5:2 Fast Diet

What to eat when on 5:2 fast diet?

On the normal days, the calorie intake should be around 2,000 calorie for women and 2,500 calorie for men.

On fasting days it is around 500 calorie for women and 600 calories for men.

You can have these as two separate meals or even split them to three.

The plan is to have low-calorie food rich in protein or fibre to control your appetite.

That would include a lot of vegetables, fish or lean meat, soups etc. Beverages would be coffee and tea and no alcohol.


There aren’t any such side effects of 5:2 fast diet. The body has enough reserves to supply energy so you won’t feel weak on fasting days.

However, in some cases you should not fast:

  • Children and adolescents
  • Pregnant or lactating women
  • Type 1 diabetics or those taking anti-diabetic medication
  • Anyone suffering from any medical condition or are unwell
  • People suffering from an eating disorder
  • People recovering from surgery
  • Patients taking warfarin


5:2 fast diet is an attractive variant of intermittent fasting.

It provides a simple option of fasting for 2 days where your calorie intake is 500-600 calories and it leads to a significant fat loss in a short time.

Despite the lack of scientific evidence, this eating pattern is recommended by many scientists and celebrities.

And to us, it seems perhaps the easiest way to incorporate intermittent fasting in your daily routine. To get started with 5:2 fast diet check out this .

Those who have tried it please share your experience with us.

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