How do intermittent fasting diets work for weight loss?

A diet that gives the “best results” for the “least amount of effort” has become the holy grail, and according to Dr Zac Turner it actually exists.

Welcome to Ask Doctor Zac, a weekly column from news.com.au.

This week Dr Zac Turner looks at whether intermittent fasting works for weight loss.

Question: Hi Dr Zac, I know I’m getting old when each day there is a new thing young people do that makes me confused, and sometimes cross. One of my young co-workers has just started a ‘fasting diet’ and it doesn’t make any sense to me – how can not eating for two days make up for normal eating the other five?

I hate to be that person but, back in my day, our diets didn’t involve starving ourselves, we simply ate meals with less calories.

Is a fasting diet actually beneficial to losing weight or is it another sham in the long list of popular diets? – Cheryl, Perth

Answer: Hi Cheryl, Thanks for your question. To put it simply, yes. Intermittent fasting, when done correctly, can be extremely beneficial to losing weight because it trains the body to not store fat.

The human body is a lazy machine, it is always trying its best to use the least amount of energy as possible. Intermittent fasting is all about changing our physiology from storing to utilising calories consumed, or in other words, increasing your metabolic rate.

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Intermittent fasting can be used to change your body’s physiology.

Science has evolved further than the traditional diet. Bio-Medical scientists, like myself, have discovered an ongoing calorie deficit trains the body to store fat, not burn it. The first time you diet, you will lose weight. But now your body is on the lookout for another extended period of calorie deficit, and when you diet again, it will be alerted and store as much fat as possible. Very frustrating, I know, but it all has to do with our origins.

Fasting diets may seem ‘modern’ but, believe it or not, the science behind it goes all the way back to our hunter-gatherer ‘caveman’ times.

Back at the start of our evolution, we would go-out and hunt for food to grow, and more importantly reproduce. It would drive our ancestor’s evolution as their bodies developed mechanisms to cope with unsuccessful hunts.

Some days our ancestors wouldn’t have caught any food, and so their bodies evolved to deal with that dilemma by storing fat and using it in times of scarcity. By fasting for a short period of time, you activate the ancient processes of your body. Any stored calorie and what you consume on non-fasting days are more effectively burned on fasting days. Essentially, the least amount of effort for the best results.

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Fasting can be used to burn calories from non-fasting days.

Nearly all the positive effects of intermittent fasting derive from the process of metabolic switching. After 10-12 hours of fasting, the body depletes its supply of glycogen and ketones. Glycogen is stored glucose, or sugar, and ketones is a type of fat. This switch in levels triggers immune signals, hormones, and other chemicals in our body.

By fasting, your blood insulin levels drop significantly which, you guessed it, facilitates fat burn. Your cells begin to repair themselves and remove waste. Human growth hormone (HGH) levels will rise which helps burn fat and gain muscle.

There are three popular methods for intermittent fasting:

16/8 method – This involves skipping breakfast and restricting daily eating to eight hours. An example would be 1-9pm. You fast for sixteen hours in between, hence ‘16/8’.

Eat-Stop-Eat: Fasting for 24 hours, once or twice a week. For example, by not eating from dinner one day until dinner the next day.

5:2 diet: You consume only 500-600 calories on two non-consecutive days of the week but eat normally the other five days.

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Dr Zac Turner says intermittent fasting is not for everyone.

It’s important to say that intermittent fasting is not for everyone. If you are underweight or have a history of eating disorders, you should not fast without consulting with a health professional first. A limited number of studies have indicated women do not benefit from fasting as much as men do, with some registering menstrual problems and worsened blood sugar control.

Cheryl, I recommend you speak with your doctor to check to see if fasting is right for you. Pick a method and stick to it for a while, and hopefully you will see great results. Ask your co-worker for tips.

Dr Zac Turner has a Bachelor of Medicine and Bachelor of Surgery from the University of Sydney. He is both a medical practitioner and a co-owner of telehealth service, Concierge Doctors, and is also a qualified and experienced biomedical scientist.