Can we really ‘eat, fast and live longer’?

School Of Nutrition Posted Sep 16, 2013 Future Fit Training

The science behind intermittent fasting and the 5:2 diet. This year saw the rise of the ‘5:2 Diet’ based on the concept of ‘intermittent fasting’. The diet advocates that by eating ‘normally’ for 5 days per week and ‘fasting’ for 2 days per week, you will lose weight...

Can we really ‘eat, fast and live longer’?

Each year, particularly post-Christmas, there seems to be some new fad diet that’s swamping the media endorsed by A-list Hollywood stars who apparently swear by it. This year saw the rise of the ‘5:2 Diet’ based on the concept of ‘intermittent fasting’.

The diet advocates that by eating ‘normally’ for 5 days per week (based on 2,000 kcal/day for women and 2,500 kcal/day for men) and ‘fasting’ for 2 days per week (500 kcal/day for women and 600 kcal/day for men), you will lose weight and may also experience a reduction in certain biological risk factors such as blood pressure, cholesterol levels and blood glucose readings. Here we explore the theories behind the hype and the pros and cons of eating in this way.

What’s it all about?

A BBC Horizon documentary called 'Eat, Fast and Live Longer' presented by Dr Michael Mosley (a journalist with a medical background), pushed the 5:2 diet into the spotlight. During the programme he experimented with intermittent fasting and there was no doubt that changes occurred to his body, both internally and externally.  However, the results were based on one person over a short period of time.

‘’Eat what you like most of the time” [1] is the tag line for Michael Mosley’s book that followed the programme and, of course, this does sound easy. The idea that you can eat and drink whatever you like for 5 days a week and still keep fit and healthy is appealing. However, the fact that you’re limited to 500-600 kcal a day for the other 2 days may not sound so attractive. You are advised to choose your ‘fast’ days carefully and use days where you have an ‘easy day’ planned, rather than days where you need to be busy with work, exercise or social occasions. This raises questions straight away about how you may feel on the ‘fast’ days!

What can you eat?

A typical ‘fast’ day menu might consist of ham and scrambled egg for breakfast, grilled fish and vegetables for evening meal and nothing in between except water, black tea or coffee and green tea. Reports of people having very low energy levels, becoming faint with hunger, irritable and unwell during the fast days are not surprising, but on the other hand some people have had more positive effects and report that they learn to embrace and even ‘enjoy’ the feeling of hunger and that their appetite decreases on the normal eating days [2].

The concern was posed that eating in this manner might trigger people to end up binge eating on the normal diet days, undoing the good of the fast days.  However, a study by the University of Illinois found that people only ate around 10% in excess of the calories they needed on normal days [3].

How can intermittent fasting benefit our health?

Much of the published research into the potential preventative effects of intermittent fasting involve measuring biological markers associated with chronic disease, such as insulin-like growth factor-1 (IGF-1) – known to be associated with cancer.

The National Institute on Aging in Baltimore, USA has been investigating and their studies reveal that going without food can lower IGF-1, which may help protect the brain from Parkinson’s disease, Alzheimer’s and other conditions [4] [5].

What do the experts say?

British Dietetic Association spokesperson, Rick Miller,indicated thata variety of research is currently being carried out on the effects of IGF-1 and long-term health. So far there is little real evidence with most studies being carried out on rodents and over short periods of time with no guarantee of transferrable application to humans and ‘real world’ health outcomes.

Others report that 5:2 diets will only be suitable for those who are in good physical shape and who do not have any underlying health conditions. The days of starvation can have a severe impact on daily life. This type of diet is not suitable for women who are pregnant or trying to conceive, people who suffer from diabetes, low blood pressure or any history of eating disorders [6].

The NHS does not recommend intermittent fasting as a viable method for losing weight. Medical opinion maintains that the only way to lose and manage weight successfully is a sensible, healthy diet and active lifestyle [7].

In the future it may be found that the reduction of IGF-1 will have positive effects on long-term health, but this diet is not a realistic method of weight loss for most people and more research is required to establish the effects of intermittent fasting [3].


So it’s fair to say that beneath the fierce marketing and media hype surrounding the 5:2 diet, for every person reporting success and wellbeing, there’s equally an opposite. Currently there is simply not enough good quality, long-term evidence to say whether following a 5:2 diet is beneficial or harmful. Only time will tell whether a growing body of research and continued interest will make this diet one that’s here to stay.  Or, like so many others that have gone before it, come next Christmas will there be a new craze to write about!?


1.    The Fast Diet: The Secret of Intermittent Fasting - Lose Weight, Stay Healthy, Live Longer by Dr Michael Mosley and Mimi Spencer


3.    Varady KA, Hellerstein MK, et al. Alternate-day fasting and chronic disease prevention: a review of human and animal trials (PDF, 118.6KB). American Journal of Clinical Nutrition. Published online 2007     

4.    Mattson, M.; Wan, R. (2005). “Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems”. The Journal of Nutritional Biochemistry 16 (3): 129–37

5.    Harvie M., Pegington, M., Mattson, M.P. et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomised trial in young overweight women. International Journal of Obesity. Published online October 5 2010

6.    Young, E.: Hunger games: The new science of fasting, New Scientist, 2 January 2013


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