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Intermittent fasting – what’s all the fuss about?

Intermittent fasting – what’s all the fuss about?


The media loves a bit of controversy. No diet has caused as much controversy recently as intermittent fasting (IF). This type of eating protocol can also go under the names of the 5:2 diet, warrior diet, alternate day diet etc. but what’s the nuts and bolts of IF? How do you do it? And is it really as good as everyone says. Let’s take a closer look.

IF is defined by Wikipedia as ‘a pattern of eating that alternates between fasting and non fasting’. This seems a little vague to me, as it seems like saying; IF is not eating followed by eating… That’s what I do everyday???

I’ll try my own spin on the definition by saying it is; ‘an eating protocol of periodised non-eating followed by eating’. Although I’m not sure that sounds much better. Let’s try and get a feel for what it is.

The infamous 5:2 diet.

Whereas the research surrounding the 5:2 diet is still somewhat light, there is plenty of other research on different forms of IF out there. Some have positive improvements on reported hunger and cognition, while some have reportedly improved blood markers body composition. We must listen to the actual research and not simply the media though. The original idea behind the 5:2 made clients stick to 600kcals per day and eat a controlled Mediterranean type diet on the off days. Hardly a ‘fast and eat what you like’ protocol. Sounds like if something’s too good to be true, it usually is! Having said that, plenty of people have anecdotal success with it, and I haven’t tried this method of IF so I can’t really comment…

What does the research say?

Research does tend to suggest that IF improves health markers and body composition in overweight or obese individuals, although actual studies are thin on the ground, it’s also worth noting that these results have been shown in healthy normal weight adults too. It’s hard to really draw wider conclusions on the efficacy as it’s still a growing body of research, and there in lies the problem…

 The problem with IF research

IF research in mice and rats is quite common, as is research on Muslims in Ramadan. While IF we are talking about does somewhat pertain to Muslims who train with us, we certainly don’t train any rats!!! I will say this though – much can be drawn from animal models of research, and we should not be too hasty to discard the evidence that suggests improved cholesterol, insulin sensitivity, fat mass and other such markers of health are common in IF animal research. After all, our medicines are developed from animal studies – why not our nutrition? So if you like the idea of IF let’s debunk some of the myths…

Breakfast is the most important meal of the day. Skipping breakfast / meals will slow your metabolism.

No it won’t. In a review by the International Society of Sports Nutrition on meal frequency they found no relation between meal frequency and metabolism. Stoking the furnace to keep metabolism up is just another gym-myth. One I will say I have been guilty of perpetuating from time to time. So what does this mean for you? Well, three meals or six – it’s up to you. If you want to skip breakfast go ahead. It won’t slow your metabolism.

 You will lose muscle ‘go catabolic’.

Fasting in obese and non obese subjects hasn’t shown this. Although more research is needed, there appears to be no cause for concern. Cortisol increases in fasting Ramadan athletes have not been reported greatly in research, in fact most reviews find metabolic changes insignificant.

You’ll lose concentration / be hungry all the time or be very tired.

Well the literature here is mixed. While some neurobiologists seem to agree that IF and calorie restriction improve brain health and cognitive function, the research on Ramadan athletes appears to show a slight reduction in cognition. However, it should be noted that hydration is key to concentration, and during a Ramadan fast no water is allowed. This might be a reason for the loss of concentration. As other studies on IF have shown increases in cognition while fasted. As far as feelings of hunger go, a study by Varady actually noted a decrease in reported hunger in participants using an alternate day fasting protocol.  Try it for yourself and see, personally I feel that it has improved my alertness, and I don’t feel hungry –  but that might just be me.

You’ll store fat as you go into starvation mode.

Turns out this is utter rubbish. In actual fact fasting will increase lipolysis (fat burning) and breaking the fast – especially with carbohydrate will turn off your fat burning energy pathway. As already stated we know that meal frequency has no effect on metabolism or fat storage. It’s again an unfortunate myth that’s perpetuated through the ages!

 It will effect your performance.

Again the research here is inconclusive. While common sense (we all know how dangerous that can be) tells us fasting will effect performance, the research often suggests otherwise. However we do know that nutrient timing is key to develop our strength and body composition long term so could this be effected by IF? Hard to say really. This is a measure  that hasn’t really been put into any long term practice yet. While IF could potentially effect levels of muscle glycogen, and therefore potentially effect high intensity performance, it’s worth noting that ketogenic diets do this anyway and have no reported effect on strength or power performance in the long term, only in the early stages of adaptation to the new diet. Food for thought.

Different protocols of IF

We could be here all day… Some people follow 16:8 (16 hours fast, 8 hour eating window) some follow 5:2, some alternate day fasting (ADF) basically there are many forms of IF and which one suits you and gets you the best results is probably the one that you should stick to. It takes experimentation and time to get used to. Remember – hunger isn’t necessarily a bad thing from time to time! Don’t panic if you start feeling hungry, those feelings eventually subside (so says the research and my experience).

Here’s the take home…

IF appears to be a way of improving your body composition and health. However, it’s one of many ways. Whether you prefer eating 3 square meals, six meals or simply doing a form of IF, your body composition and health goals can be met using any form of dietary protocol. So is it the next big thing?

 Newsflash – you might already be doing it

When I listen to my clients it turns out some of them have been doing it for years… How many people do you know that skip breakfast? This turns out to be IF. So the truth is this – it’s not so much the way you eat, but probably what you eat and when you eat it! Eating crap is going to effect body composition, whether you IF or have your six meals per day. In terms of you athletes out there, many have been doing IF by accident. Up early, train fasted and then eat later in the day. No big deal, their performance hasn’t waned nor have they lost all muscle from going catabolic.

It’s essentially just another tool in the toolbox. If it suits you, use IF. It maybe best as a form of quick and easy calorie restriction or simply a tool to use when you have particularly busy days. My advice is this – monitor calorie intake, monitor (more importantly) macronutrient intake, reduce carbs for you fat burners and choose to only eat when you have access to good food. When we all sit down and think about it, the answers were there all along.

Thanks for reading.


 *If you want to learn more about IF and how it might fit into your training regime, email Brett and book in for a nutritional consultation today. 



Bounty et al. International Society of Sports Nutrition position stand: meal frequency Journal of the International Society of Sports Nutrition. 2011

Chaouachi et al. Effects of Ramadan Intermittent Fasting on Sports Performance and Training: A Review. International Journal of Sports Physiology and Performance, 2009, 4, 419-434

Chennaouia et al. Effects of Ramadan fasting on physical performance and metabolic, hormonal, and inflammatory parameters in middle-distance runners. Applied Physiology, Nutrition, and Metabolism. 2009

Heilbronn et al. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. American Society for Clinical Nutrition. 2005

Maarten R et al. Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism. American Society for Nutrition. 2009

Maughan et al. Ramadan and sport: The effects of fasting on metabolism and performance. British Journal of Sports Medicine 2010

Stote, et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. American Society for Clinical Nutrition, 2007.

Varady & Hellerstein. Alternate-day fasting and chronic disease prevention: a review of human and animal trials.  American Society for Clinical Nutrition 2007

Varady et al. Effect of exercising while fasting on eating behaviors and food intake. Journal international society of sports nutrition. 2013