Not so Fast - obesity expert Dr Nick Fuller weighs in on the latest trend for dropping the kilos

Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.

New research says that fasting – a practice whereby you don’t eat for a certain window of time – is the latest and greatest way to improve our health and lose weight.

It's proponents, who include Dr Michael Mosley, say that as well as losing weight, fasting clears our minds, reduces inflammation and even delays the ageing process. 

They are big promises, but is fasting actually a good thing? 

1. It’s difficult to sustain

The latest research published in Cell Metabolism suggesting that fasting will help us lose weight follows a clinical trial in which healthy people in a normal weight range were asked to refrain from eating for 36 hours, followed by a 12-hour window of unlimited eating. 

It's based on evolutionary principals - our ancestors would go long periods without food and then gorge when food was available. However, in the modern-day environment whereby high-calorie, nutrient-poor but delicious food is on every corner, we have a difficult time saying ‘no’. 

It's hard enough to refuse a piece of office birthday cake or a sliver of brie before dinner at the best of times, imagine if you were 34 hours into starving yourself! You might be able to do it once, but over time, it wears thin. 

This is what scientists refer to as an ‘evolutionary mismatch’; our genes haven’t changed over time, but our environment has. Abstaining from food for 36 hours every second day is not sustainable, despite any health benefits we might gain from such a fasting approach.

2. It’s a quick fix

Much like all the current, popular fasting methods, whether it be 5:2, 16:8 or any other time-restricted feeding, we like the concept of this dieting approach because it’s easy to digest, so to speak. It's a quick fix and doesn't require long bursts of willpower - just 36 or however many hours at a time.

But all these approaches are simply a fancy way of cutting calories from the diet to achieve the quick drop on the scales we hope to see. Much like the improvements in health you will experience short-term when the weight drops, it’s all downhill when the body starts to fight the weight loss and you end up fatter than before you began. This is because our bodies learnt to shut down and store fat during times of deprivation, so whenever you impose a calorie restriction, your body will fight the weight loss and ensure you go back to your starting point (and store a little extra fat for the next bout of starvation you will impose).

3. You’re likely to binge on non-fasting days

Whenever we go long periods without food, we seek out calorie-rich foods that are high in fat and high in sugar. Again, this is engrained in our biology and leftover from our time as hunter-gatherers. The biggest caveat of this new study was that it was only four weeks duration. We can all stay disciplined for a short period of time, especially when under the scrutiny of clinical researchers, but eventually we will seek out those foods that make us feel good.

About Dr Nick Fuller

Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.