Intermittent Fasting - a fast way to lose weight or just another fad?

Continue to eat the foods you like, lose weight and improve your health markers. If Intermittent Fasting (IF) really can offer all these benefits, then why isn't everyone doing it?

Intermittent Fasting was introduced to the public at large by the British Dr Michael Mosley and his 2012 BBC Horizon programme. Since then there has been a wealth of copycat diet plans and books on the subject.

But despite the explosion of diet plans one of the main problems with the diet is that it is still relatively new - if you ignore wandering around in the desert for 40-days - and as such there isn't an abundance of scientific studies backing it up. Indeed at the time of writing the NHS still doesn't recommend the diet, citing a lack of evidence behind it.

However the conclusions of existing studies are really quite positive.

In her 2010 study British fasting expert Dr Michelle Harvie found that intermittent fasting was as good as general calorie restriction for reducing leptin, total LDL cholesterol, triglycerides and blood pressure.

Harvie later found that intermittent fasting potentially lowered the risk of obesity-related cancers such as breast cancer.

In a more recent animal fasting study Dr Valter Longo concluded that fasting led to greater insulin sensitivity, and reduced levels of blood pressure, body fat, insulin, glucose and inflammation.

Longo also found that fasting regimes could help prevent heart attacks, diabetes and strokes.

According Longo these benefit arise because IF triggers the body's 'adaptive stress response' which results in an enhanced ability to cope with more severe stress and counteract disease processes.

Dr Jason Fung believes the true benefit of IF it is the effect of the diet on insulin and insulin resistance is the real benefit of IF.

He says: "The short answer is that the beneficial hormonal changes that happen during fasting are entirely prevented by the constant intake of food."

Referring to Harvie's study Fung points out: "There is a clear, substantial improvement in insulin levels favouring the IER (Intermittent Energy Restriction" group. Even more impressive is the change in insulin resistance.

"This is the long term problem of weight loss. It is the intermittency of the diet that makes it effective."

It is worth pointing out that both Harvie and Longo note that studies have so far focussed mainly on overweight people and so the jury is still out on whether IF can be recommended to the entire population.

Some have argued that the positive effects seen with fasting can be attributed to simply the general restrictions of calories, as a reduced calorific intake brings weight loss which then brings a raft of health benefits.

Others say that this thinking has things the wrong way round and that the weight loss and the improved health markers are actually because of the act of fasting.

Interestingly there are splits within the fasting camps itself. Dr Krista Varady, one of the IF experts Dr Mosley uses to substantiate his diet, has demanded Mosley remove her work from his book after claiming that her studies focus only on every other day fasting and her work offers no direct evidence in favour of the 5:2 diet.

She says: "The fast diet is about {Mosley's] experience. But unfortunately he actually used all of my research on alternate day fasting to support all of his points. Scientifically you can't take studies that look at three or four days fasting a week like mine and say it's the same thing and that you're going to get the same health benefits when you just fast two days a week"

When we consider both Varady and Mosley have diet books to promote perhaps this squabbling shouldn't appear surprising.

There are also some researchers who suggest that the 5:2 diet is unhealthy.

In an experiment on mice, researchers at Norway's National Institute of Nutrition and Seafood research (NIFES) in Norway, found that mice who were subjected to intermittent fasting while having access to an obesity-inducing diet, i.e those who were allowed to pig out on non-fasting days, put on more weight than those who didn't fast but had access to the same diet.

Varady also questions Mosely's claim that fasting allows you to eat whatever you want on non-fasting days. She contends this isn't true and that it's not soley how many calories you eat but from what source that is important.

So should you go on the 5:2 diet or some other form of fasting?


I've tried both the 5:2 and Alternate Day fasting and had mixed success with both.

In both cases I have lost fat at a fast rate. This is, of course, a good thing.

On the other hand I found that I soon allowed myself to fall into a 'famine and feast' pattern in which my low calories fasting days were followed by indulgent days where I allowed myself the treats I knew I should be trying to give up.

Consequently I found that when I stopped following an IF diet I now wanted to continue eating my calorie laden treats.

I was surprised at how easy it was to skip breakfast or lunch and the hardest part of missing these meals is knowing that you don't have some nice food to break up your day.

The flip side of this is that it's surprising at how much more time there is in a day when you don't have to worry about making food or eating.

As such, contrary to Mosley's claim's I would only recommend IF as a short-term weight loss system, adding the caveat that it might lead to weight gain when one stops following it.