Many fans of the 5:2 intermittent fasting diet have experienced weight loss success, and preliminary scientific studies into the diet are validating their results. But there is still a lot to learn about what intermittent fasting means for long-term health and eating habits. Today we take a look at the pros and cons of the 5:2.
Studies have shown intermittent fasting can fend off illnesses including cancer, diabetes, heart disease and neurodegenerative disorders and may improve insulin sensitivity - but there is still a lot more to learn.

Some studies have shown intermittent fasting can fend off illnesses including cancer, diabetes, heart disease and neurodegenerative disorders and may improve insulin sensitivity – but there is still a lot more to learn.

This blog was originally published on the Total Wellbeing Diet website. 

Fans of intermittent fasting programs – think the 5:2 diet – often find they have success with weight loss, so today we are taking a look at the pros and cons of this kind of diet.

While fasting technically refers to not consuming any food or liquid at all, intermittent ‘fasting’ diets, like the 5:2 diet, do involve very minimal calorific intake on the fasting days – we’re talking around 2000 kilojoules all day, compared to the daily recommended intake of around 10,000 for men and 8,700 for women.  These diets run on the premise that you fast for 2 days of the week and consume as many kilojoules as you like on the non-fasting days.

While 5:2 is the most popular configuration, others find they have more success following a 4:3 or 6:1 ratio of non-fasting to fasting days.

The surprising news is, studies are suggesting these diets are successful in achieving weight loss. Even more surprising, Dr Manny Noakes, Research Director of our Food and Nutrition Flagship, says research is revealing people don’t eat more than they usually would on the non-fasting days – which was what many experts expected to see.

The research is still limited, but Dr Noakes says animal studies have been optimistic. Some of these animal studies have shown intermittent fasting can fend off illnesses including cancer, diabetes, heart disease and neurodegenerative disorders and may improve insulin sensitivity.

Dr Noakes says she herself would not discourage someone following such a diet that was seeing success, though she cautions there is still a lot to learn before it gets the seal of approval.

“If people who are overweight have struggled to lose weight following other diets, and they find this works for them, then that is great. Weight loss, particularly belly fat, has many health benefits – visceral fat is involved in disrupting blood-sugar regulation and is associated with high cholesterol levels. It’s also a risk factor for developing Type 2 diabetes and heart disease.”

On the flipside, Dr Noakes says what we don’t yet know about intermittent fasting is what these diets mean for long term health.

If the person is simply losing weight because they are effectively cutting a lot of kilojoules from their weekly intake, but they are still eating poorly, then I’d have to argue they still need to address their eating habits for longer term health gain.

She says while restricting your kilojoule intake is a guaranteed way to lose weight, cutting back indiscriminately can lead to an unbalanced, unhealthy diet, and recommends a more balanced approach. “It’s important not to cut key food groups including dairy, grains and cereals – you’ll be missing out on some important nutrients essential for good health.”

To summarise the pros and cons:


  • Loss of body fat/ weight for overweight people is of health benefit in general.
  • Early research shows contrary to what scientists expected to see, people do not consume more kilojoules on the non-fasting days.
  • Intermittent fasting diets seem to be as effective as calorie restricted diets for weight loss.
  • There is early research to suggest it is effective in curbing cravings.
  • It provides an easier weight loss plan than standard kilojoule restricting diets – there is no weighing or ‘forbidden’ foods to worry about – on the fasting day, the limited calories will be accounted for very quickly and there are no restrictions on non-fasting days.


  • Fasting diets don’t change the way you eat – there is no evidence at this stage that suggests people eat healthier food than they did prior to starting the diet. While maintaining a healthy body weight is important for good health; a nutritious diet offers important vitamin and minerals.
  • There is limited research on the long term effectiveness – or any long term health issues related to intermittent fasting.
  • This lack of research means we don’t know who the diet works for and who it might not – for example, what medications or illnesses it may interact badly with.
  • Unlike diets that make healthy lifestyle changes – like the Total Wellbeing Diet – fasting diets do not provide advice on how to eat for optimal health, in a way that is sustainable in the long run.

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  1. I tried the 5:2 diet last year but was a bit half hearted about it. Despite that I went from 91.3 down to 86.2 over 3 months. I found it relatively easy and started to think more carefully regarding portion size and snacking. I have Just reread the Dr Michael Mosley book and can now see a few points I previously missed. So I have started again and now target 16 hours without food on the so called “fast days”, which what I have been reading about the gut can be beneficial. I have found no loss of energy and the meal suggestions helpful and nutritious.


  2. I can’t believe you are still pushing dairy as essential for humans. it’s 2016…. let’s talk animal experiments… what other animal consumes dairy its whole life?

  3. My husband and I used the 5:2 diet to loose 25 and 12 kgs respectively. We have always had a good diet but have obviously over consumed…we find we are now more conscious of portion size and of when we are over eating. If the scales go back up a kg or 2 we use the 5:2 diet to rapidly come back down. Interestingly we have quite a lot of energy on the calorie restricted days.

    1. that´s great Virginia!

  4. So, in fact, there are no REAL cons………….

  5. A long time ago, T S Chang (Div of Animal Genetics) did an experiment with a lot of sheep. Overlayed on the genetic differences and to work out the best way to obtain the weight of a small ruminant, one third were weighed (monthly?) without feed deprivation, one third were deprived of feed for one day and the remaining third were deprived of feed for two days before weighing. When they were slaughtered (Wt.?) the 2-day feed -deprived group had much less sub. cutaneous fat. So, may be starvation does work??

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