Does the Fast Diet live up to the hype?

May 13, 2014

in diet, healthy eating, lifestyle, naturopathy, weight loss

As a naturopath and health coach I cringe every time a diet book hits the headlines. One day there’s a book spruiking a low carbohydrate diet, the next it’s high protein, no fat or high fat.

In the past year Dr Michael Mosley’s Fast Diet, also known as the 5:2 diet, attracted a lot of attention. As so many credible professionals have endorsed it, I thought I’d take a closer look. So how does it rate?

What’s it all about?

This is essentially a weight loss program, borrowing the psedoscience of the intermittent fasting regime. There is a belief that if you eat significantly less than the average daily recommended kilojoules you will live longer. With the intermittent fasting-based Fast Diet, instead of eating less every day the week is broken into two severely food restricted days (2400 kilojoules /600 calories) and five days when you can eat and drink anything you wish.

Intermittent fasting is not a novel concept – animal studies on it begun in 1945. Nor is the 5:2 model new. MD Bert Herring published The Fast 5 diet in 2005, describing it as “one approach to a weight-reduction dieting”.

Whose spruiking it?

Mosely is a psychiatrist turned television producer/presenter who set himself up as a guinea pig following the 5:2 diet for the sake of an Horizon documentary. His co-author Mimi Spencer is a fashion journalist. Neither have had any significant  nutritional training.

The claims

Mosley has claimed intermittent fasting has the following benefits:

  1. As well as offering a fresh approach for people trying to lose weight, intermittent fasting has been developed by scientists wanting to help people reduce their risk of developing diabetes, dementia and cancer.
  2. The concept has been most extensively studied in volunteers who are obese or overweight. In a recent study of 115 overweight women, those who restricted their calories two days a week lost more fat and had a greater improvement in biomarkers related to breast cancer risk than women who were conventionally daily dieting.
  3. The benefits in people who are not overweight are less clear because there have been fewer studies. In one experiment, a number of fit young men were asked to practice intermittent fasting without losing weight for a few weeks. During that time they saw improved insulin sensitivity, a marker for reduced diabetes risk.
  4. Animal studies have shown that intermittent fasting reduces risk of dementia. Human studies have just begun.
  5. Fasting also has a spiritual dimension and has been advocated by most of the great religions

Source: Fast Diet FAQ

Demystifying the claims

In an era of evidence-based medicine, health claims framed in fuzzy language tends to trigger alarm bells

Looking at the claims:

  • The first point doesn’t actually claim that the diet reduces the risk of dementia, diabetes and cancer. Rather it’s devised by scientists “wanting to help people” reduce those risks.
  • The second, omits the fact that obese women are at greater risk of breast cancer and that any significant weight loss, regardless of regime, will reduce those markers. Furthermore there are no studies that can demonstrate that intermittent fasting lowers a woman’s risk of developing breast cancer.
  • The third point at least admits there’s a paucity of hard evidence that people of average weight have any prolonged health benefits from intermittent fasting. Also testing for diabetes markers in non-diabetics is irrelevant and doesn’t necessarily correlate with those who have the disease.
  • The fourth point alludes to a mouse study, showing reduced calorie intake delayed the onset of dementia in mice that are bred to develop the condition. There is no evidence of this being replicated in humans with or without the gene
  • And lastly, is religion the best endorsement for a diet? Are they promoting the Fast Diet as a spiritual practice, for weight loss, health prevention or longevity?


“Every fool can fast, but only the wise man knows how to break a fast.”

G.B. Shaw

What you eat, rather than just the total kilojoules, needs more scrutiny. Three foods that reoccur in almost every suggested 5:2 diet plan are eggs, bacon and smoked salmon. The first two are high in saturated fat. Bacon, with or without the fat trimmed, is a low in good nutrition and high in salt and cancer-causing nitrosamines. Almost all smoked salmon in Australia is from farmed salmon which has a different fat profile to wild.

It might encourage binging

It could encourage participants to see the non-restricted intake days as a free pass for five days, when nutritious food choices go out the window. This may lead to some less-than-healthy binging. As an experienced health practitioner, I’m skeptical about the foods some people choose to compensate for the fasting days.

Are you using the diet to live longer or for weight loss?

The majority of  questions I’ve had about the diet have been from women, under (or just on) normal weight, with a history of dieting and over-exercising.  To date, no one has asked about longevity or healthy living in relation to following the plan. This suggests, whatever the intentions, it’s perceived by the public as another diet book, rather than a health plan.

Adapting the Fast Diet: a healthier option

Rather than focusing on the energy count two days a week, how about having a day of raw or steamed plant-based food each week? Then for the other six days be conscious of serving sizes and follow more of a ‘points’ approach – looking for a balance of lean good quality protein, true wholegrains, masses of vegetables, some fruit and only a little added sugar and animal fat.

In most cases weight-loss comes down to tweaking the ratio of energy in (what you eat) with energy out (how you move your body). Any diet that results in burning more fuel than you consume should lead to weight reduction. On that basis, the 5:2 diet should work as a weight loss plan, depending on the food choices you make on the five non-fasting days and if you continue to exercise.

But is this intermittent fasting the healthiest way to loose and maintain weight? My nutritional training questions the counter-intuitive nature of potentially consuming unrestricted animal products and not changing unhealthy eating (and drinking) patterns.

Always bear in mind it’s not just the number of kilojoules you consume but the quality of the food it’s in that impacts your health and longevity.

The Fast Diet: The Secret of Intermittent Fasting  -  Lose Weight, Stay Healthy, Live LongerConsider a therapeutic fast rather than a ‘diet’

A ‘fast’ traditionally means going without food for a period of time, consuming only water or medicinal liquids instead. The idea is to give your digestive system some time out for recuperation and repair.

But fasting was always done in conjunction with other therapies, usually massage, hypdrotherapy and physical rest. It was never solely about not eating. It’s rare to find someone who wants to spend their holiday taking on such a regime.

Another option is a modified fast, or as I call it ’spring cleaning’. You can read more about it here.


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