intermittent fasting

A lot of our members have been asking us about Intermittent Fasting and if it works.  As fitness professionals we refrain from prescribing fad diets but we have done some research into this trending topic and liaised with nutritionists for their thoughts so that we might share it with you.

The magic of the 12-hour fast

Twitter CEO Jack Dorsey fasts for 22 hours in the day and has regular “water only” days as he claims this hones his ability to focus and work harder.

Because Iconic Health Club members are not billionaire techies obsessed with productivity (well most of them anyway!) we won’t be discussing that kind of fasting here but rather take a look at more sustainable options for people with lives to lead and spinning classes to get to.


I met up with a friend last week I had not seen in months and she looked fantastic. Her skin was glowing and had she lost weight?

She told me she had lost half a stone since she had decided to fast for 12 hours a day and, as she is asleep for most of it, there is little pain involved.

She said it had made her re-examine her attitude to food and realised the evening for her was prime time for unhealthy snacks.

That night we were tucking into tapas at 10pm and she was lowering her second glass of red wine so was she breaking her diet?

No, tomorrow she won’t have breakfast until 11am and then is back on track.

Most evenings she would not eat anything after dinner at 7pm until breakfast twelve hours later and had lost the weight without changing her diet ; apart from cutting out the 11pm toasted cheese sandwich.

Many ways to fast

Intermittent Fasting (IF) is everywhere but until now I had filed it away as drastic behaviour but now I was not so sure. So, what is it exactly?

Well, it is simply only letting yourself eat for a certain window each day.

For instance if you do IF for 12:12 this means you fast for 12 hours and the other 12 is when you eat all your meals.

If you are fasting for the much more unsustainable 16:8 you have to squeeze in all your meals into an eight hour window.

That means no calories from drinks during your fasting window. So water, herbal tea or black coffee is ok but, sadly, no alcoholic beverages.

The good news is you can take a flexible approach (within reason), and say if you do have a glass of wine and hit the crackers and cheese at 11pm one night,  then it’s black coffee for breakfast and you would delay eating anything until 11am.

You can also do the 5:2 diet which means you eat fairly normally for five days and then have two where you only consume 500 calories for women and 600 for men.

Dr Michael Mosley’s Fast diet is a well known example and if you think you could manage the two days where you are very strict with your food, this could be for you.

Eating window not a free-for-all

Irish dietitian Conor Kerley says there are many ways to fast intermittently but remember that to maintain good health you can’t just eat anything you like when you get the green light.

“There are many ways to fast intermittently for example skipping breakfast, or eating breakfast late, which means fasting since dinner the previous day. Another example is having an early evening meal. Intermittent fasting can be beneficial (for weight management) if it suits your schedule and preference but remember, the amount and type of food eaten when not fasting will always be important!”

Kerley would advocate trying to lower red meat consumption, as there is evidence that eating a lot of red meat can lead to health problems, and instead increase plant sources of protein such as legumes (such as lentils, peas), beans and nuts.

He would also recommend including enough fibre in your diet which makes sure your body releases energy slowly and will keep you fuller for longer.

Foods high in fibre are not processed, and as you do not actually digest fibre it means you can eat quite a lot, but still keep the calorie count low.

We need 30 g a day but many of us don’t get that.

This looks like an apple and a banana at 4g each, a cup of raspberries which is 8g, the same amount of broccoli will get you 5g and a cup of peas 8.8g.

Could you hack two meals a day?

The food we eat is broken down by enzymes in our gut with refined carbohydrates quickly broken down into sugar which our fat cells use for energy. If our cells don’t use all of this we store it as fat.

Sugar can only enter our cells with the hormone insulin so between meals if we don’t snack our insulin will go down and fat cells will release stored sugar as energy.

I know the approach of eating twice a day would not work for me as I would not be able to cope without either lunch or breakfast, but many health professionals, such as running guru Eric Orton, swear by this and say not snacking gives your body a chance to burn fat.

The Wyoming based running coach trains runners for marathons and ultramarathons and told me he believes fasting is very good for you and having your blood sugar constantly elevated is not a good thing.

He suggests you skip breakfast and eat only two meals a day.

“This intermittent fasting will do wonders for your body to recruit fat burning capabilities for your running and your marathon performance”, he said.

His other diet suggestions for good health include eliminating all refined sugars and carbohydrates, with a focus on lots of fish, vegetables and good fats.


Proponents of the aforementioned 5:2 diet include increased life span and cognitive function and protection from chronic diseases such as type 2 diabetes.

Speaking recently on the Healthy Beast podcast Dr Micheal Mosley discussed how cutting your food intake could help those at risk from diabetes.

“Your body is constantly having to produce insulin and this ultimately causes insulin resistance. This causes your cells to rebel and you need to pump out more and more insulin and that takes you down the road to various cancers and particularly type 2 diabetes, “he said.

He also talked about the process of autophagy which is when your body starts to break down old cells and repair itself . This only starts to kick off 7-8 hours after you have stopped eating.

So the message here is the less often you eat, the less often you raise insulin levels. Insulin is the main hormone associated with fat storage so you are likely to lose weight.

Some diets such as the keto diet avoid insulin spiking foods and keep insulin low this way so the body switches to using stored fat as its main fuel source.

Fasting – the reality on the ground

As research for this piece I tried the 16 hour fast so had an early dinner one day at 6pm with no breakfast or any other food until 10am. This was not too bad. I did have a couple of coffees with milk (that was cheating). I did this for one day and it became way too much hassle and I didn’t like the fact that I had to eat my meals on my own.

I ended up snacking all day anyway and taking in the same calories. So that was that ; the 16 hour fast would never work for me.

The 12 hour fast was more sustainable as you could eat a late dinner at 9pm and then just delay breakfast until 9am the next day. Or eat dinner at 7pm and breakfast at 7am. That’s not too much hardship.

And if you do succumb to the popcorn and maltesers at 11pm then you have to skip breakfast and have eat again at 11am.

I tried this for a few days and actually it was nice to feel hunger for breakfast as previously I would unthinkingly eat a huge bowl of porridge no matter what time I had eaten the night before. It felt right to wait for 12 hours.

The 5:2 diet I could not manage for even one fast day. I had gone to a power pump class that morning, arrived home starving and gobbled up the 500 calories in minutes. There was no way I could not eat for the rest of the day.

In conclusion the 5:2 idea could be sustainable for you if it suits your lifestyle ; though it won’t be possible for many people to cope with the low energy on the two fast days.

The 16 hour fasts is quite drastic and I would suspect would be impossible for a lot of people to follow. But the 12 hour fast is quite doable and fits in easily with an active lifestyle.

Simple equation

Expert nutritionist Ian Marber is not convinced on the need for fasting and maintains it’s a question of physics – energy in and energy out and the reason fasting works is that you have less chance to eat.

“In my day not eating breakfast and having coffee instead was considered worrying, maybe dieting too hard.  But, call it fasting and suddenly it’s ok?  All these methods cut calories by creating an artificial window for eating, hence the success.  Fasting for 12 hours or 16 hours ; it’s all the same!”.

So it’s not the fasting that is making you lose weight but rather all those opportunities that present themselves outside of your allowed eating window.

Which makes me think perhaps the fasting 12 hour approach would work well for most people.

You still have your well balanced three healthy meals a day but it just cuts out the night time snacking which I suspect is a question of habit.

Are we getting so caught up in the dieting spin and the fitbits these days that it’s a distraction from calories in and calories out.

Figures show that nearly six in ten Irish adults are overweight or obese ; we are going wrong somewhere and perhaps giving your body a fast of 12 hours a day which will tackle the night time nibbles makes sense.

And with some flexibility once or twice a week as life is something that cannot be managed all the time and it’s important to give yourself a break.

Mary McCarthy is a freelance journalist writing for a number of publications. @maryknowsbees

All material in this document is for information purposes only and should not be construed as medical advice or instruction. These materials should not be relied upon as an alternative to any advice given by a medical practitioner or registered dietician or nutritionist. No action or inaction should be taken based solely on the contents of these materials and it is recommended that readers consult appropriate health care professionals on any matter relating to their health and well-being.