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The 5:2 or Intermittent Fasting Diet

Hadyn Luke posted this on Tuesday 17th of September 2013 Hadyn Luke 17/09/2013

Tags: Nutrition weight management


The 5:2 or Intermittent Fasting Diet – does it work

This blog investigates the 5:2 Diet – a relative newcomer to the world of weight loss diets, but one that is becoming more widely known.

Jennifer Lopez, Gwyneth Paltrow, Dom Joly and Philip Schofield are all said to have followed this diet and achieved results, bringing it to further prominence, and many personal trainers may have clients following this diet. 

Also known as the Intermittent Fasting Diet, this is essentially a regime in which a person will eat their usual diet for five days of the week and either fast or follow a low-calorie diet for the other two days. The low-calorie part of the diet is normally up to 500 calories a day for women and up to 600 calories for men, although some people choose to fast on those two days instead. 

The 5:2 Diet has been featured in the media and has been the subject of several diet books in the past year, following an investigation of the phenomenon on Eat, Fast and Live Longer, a BBC Horizon documentary broadcast in August 2012.

What does the 5:2 diet consist of?

As the diet is becoming more popular, it’s useful for a personal trainer to understand what it comprises. 

The average daily calorie intake needed to maintain weight is around 2,500 for men and 2,000 for women, according to the NHS Choices website. Men following this diet would eat up to 600 calories and women up to 500 calories on the two low-calorie days of this diet, which is significantly less than on the other five days. However, it is possible to eat two healthy meals within this lower calorie count.

While it’s possible to use up the whole day’s allowance of 500-600 calories on a chocolate bar and a sugary drink, a fitness instructor would, of course, recommend healthier options to ensure that the client has a good intake of nutrients and to help them feel as full as possible through the low-calorie days. A good example might be scrambled eggs, fruit or porridge for breakfast followed by an evening meal of grilled fish or chicken with steamed vegetables. 

Anyone following a reduced calorie diet or fasting day should also be aware of what they drink on that day, ideally restricting their intake to water, green tea and/or fruit teas. Coffee should be drunk black without sugar.

Alternative diet programmes involving intermittent fasting include week-long fasts followed by the gradual reintroduction of foods and restricted calorie juice diets.

Does the 5:2 Diet work?

The Horizon documentary reported studies that found that after a fasting day subjects ate slightly more the next day than usual but not significantly more; in other words, their overall calorie count over the week was lower than previously. 

The NHS Choices website says that: “Champions of the 5:2 diet claim that other than helping people lose weight, 5:2 diet can bring other significant health benefits.” It lists these as:

  • Increased life span
  • Improved cognitive function and protection against conditions such as dementia and Alzheimer’s disease
  • Protection from disease 

However it also points out that there is as yet limited evidence about the diet, when compared with other weight-loss regimes, including whether it is sustainable as a long-term diet option.

There are also concerns that fasting and calorie restrictions could impact on an individual’s ability to exercise, whether with a personal trainer or in a fitness class or sports team. Considering that exercise is recommended as part of a healthy lifestyle, anything that restricts exercise could be considered negative.

Studies investigating the 5:2 Diet

A 2010 study found that the 5:2 Diet allowed a group of women to lose a similar amount of weight to another group on a calorie controlled diet. A later study, in 2012, suggested positive results when looking into the diet’s effect on lowering the risk of cancers related to obesity. 

Other studies on whether intermittent fasting increases life span and reduces cognitive decline have been limited in scope and size; more research is needed to draw further conclusions.

What are the potential side effects of the 5:2 Diet

Although there hasn’t been a great deal of research on side effects, a fitness instructor would expect a client who is fasting or restricting their calorie intake to have less energy, with a potential knock-on effect on their sleeping patterns.

They should also be careful to keep hydrated by drinking plenty of water and anecdotal evidence has pointed towards a risk of irritability, anxiety and bad breath as side effects.

The 5:2 Diet is also unsuitable for:

  • Pregnant women
  • People with eating disorders
  • Those with specific health conditions, eg diabetes


If a personal trainer is working with a client looking for advice on using this diet, they will need to ensure that they are in general good health. The fitness professional should also be made aware of any calorie restrictions or fasting on days the client is exercising.

Ideally the client should consult their GP first and follow a diet plan devised by a dietician. Alternatively, a fitness instructor could recommend a programme of exercise for weight loss, coupled with a healthy balanced diet including five or more portions of fruit and vegetables a day.

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