The Intermittent Fasting diet - is the 5:2 diet the new way to get slim and healthy?
5:2, the Intermittent Fasting Diet

Intermittent fasting for weight loss is the latest diet claiming to get results. Here's how fasting to lose weight works.

The Intermittent Fasting diet - is the 5:2 diet the new way to get slim and healthy?

By Dietitian Lyndel Costain BSc RD

Intermittent fasting whipped up a storm of interest when the BBC’s Horizon programme Eat, Fast and Live Longer highlighting intermittent fasting’s (IF) potential health benefits.

Since then, an entire fasting diet industry has developed, mainly for weight loss.

IF claims to help us to not only stay slim and live longer but also ward off illnesses from diabetes to dementia, it certainly sounds impressive.  So should we give a fasting diet a go?

What is Intermittent Fasting?

There are different approaches, for example, alternating days of fasting and eating freely, or fasting on two days a week as in the 5:2 diet.

For our purposes, IF refers to eating ‘normally’ for 5 days the week, and on the other 2 'fasting days' eating between 500-1000 calories depending on the plan followed.

Does an Intermittent Fasting Diet Work?

Most of the evidence relating to the claimed health benefits of IF comes from animal studies.

This is a major reason why it’s currently very difficult to make clear statements about the diet's potential health benefits.  There needs to be more studies with humans, of longer duration.

There are some short term studies published regarding the weight loss potential of intermittent fasting. These studies only refer to a specific IF approach, popularised as the 2 day diet book.

A British study on Intermittent Fasting

Last year a British study amongst 107 overweight women (aged 30-45) was published in the 1American Journal of Clinical Nutrition.

The women were randomly assigned to follow one of two balanced weight loss eating plans. Either based on a Mediterranean diet (1500 calories) or an Intermittent Fasting diet for 2 consecutive days (650 calories) and the Mediterranean Diet for the other 5 days.

After 6 months researchers found that:

  • Weight loss was similar between the 2 diet groups (around 6kg) as was decrease in body fat and waist measurement.
  • There were similar reductions/beneficial effects on blood cholesterol, triglycerides, leptin, blood pressure, inflammation markers and indicators of breast cancer risk, and increases in ghrelin.
  • Both test diets led to modest improvements in fasting insulin levels and insulin sensitivity, with a greater effect for the 5:2 IF group.
  • At the end of the trial only 58% of those following 5:2 IF planned to continue compared to 85% of those following the Mediterranean style diet.


A second study used the same criteria but changed the 2 consecutive fasting days from being milk based to a low carb regime.  After 3 months, although the both groups lost a similar amount of weight, the 5:2 group lost a bit more body fat and better improvements in insulin.

More information can be found at:

Is Intermittent Fasting recommended?

The British study suggests that 5:2 IF can be as effective for weight loss (and for providing health benefits) as a more standard restricted calorie controlled diet, with no concerning side effects, over 6 months.  One point of difference (also found in some other studies) is the potential for additional benefits to insulin and blood sugar levels with intermittent fasting. (IF 5 2)

WLR Says:

If we are overweight, and lose some weight, then our overall body health will benefit – whichever approach we use.  

However, it isn’t healthy to follow unbalanced diets, or to greatly restrict what we eat one day, and then go mad eating whatever on other days of the week.

 Research does suggest that different approaches suit different people and trying out different approaches can initially be motivating. 

Remember however, that any dietary approach is only effective if it is nutritionally sound and can be sustained; studies comparing different popular and conventional dietary methods find that the most helpful ones are those that people can best keep to.

Whichever approach is used, remember these key tips:

  • Keep a diary
  • Structure and plan times for your meal and activity pattern
  • Learn what’s in the food you’re eating
  • Get support
  • Take responsibility
  • Stay on top of unhelpful thoughts or triggers such as ‘all or nothing’ thinking or stress/comfort eating.


1National Journal of Clinical Nutrition

Michelle N. Harvie, Mary Pegington, Mark P. Mattson, Jan Frystyk, Bernice Dillon, Gareth
Evans, Jack Cuzick, Susan A Jebb, Bronwen Martin, Roy G. Cutler, Tae G. Son, Stuart
Maudsley, Olga D. Carlson, Josephine M. Egan, Allan Flyvbjerg, and Anthony Howell
The effects of intermittent or continuous energy restriction on
weight loss and metabolic disease risk markers: a randomised
trial in young overweight women. 
Published in final edited form as:
Int J Obes (Lond). 2011 May ; 35(5): 714–727. doi:10.1038/ijo.2010.171

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