• Katie Chaplin

Intermittent Fasting

Is fasting ever a good idea? You might be surprised!

I will start with the most common questions I get regarding this topic :

· Does it breed binge eating?

· Don’t you need to eat little and often to keep your metabolism high?

Photo cred: HIIT Kitchen

To answer the second question first, it is always calories in versus calories out that dictates whether you lose weight, gain weight, or stay the same. If you choose to have all 2500 calories in the evening, or spread it across 3 meals and 2 snacks, you are still eating 2500 calories per day, and this will have the same effect on your weight.

Hunger hormones are actually released into response to routine- so if you eat a snack at 11am- you will feel hunger pangs at this time regardless of whether you are hungry or not. So initially fasting can be difficult to begin with but quickly ease as your body gets used to the change- and will adjust hormones accordingly.

With regards to binge eating- there are some people that should never consider intermittent fasting, and that is those with a history of eating disorders- the nature of the diet could easily trigger the binge-restrict cycles classical of certain disorders.


· The psychological aspects may help you lose weight. They can eat large meals- e.g. two 900 calorie meals for someone that is on an 1800 calorie diet, rather than 5 360 calorie meals, that :

1. Feel more satisfying- not feeling like you are missing out, which decreases the likelihood of making poorer choices or generally eating more later

2. The meals are so large you may find it difficult to finish-so you may end up consuming less calories

· Convenience- for example

1. If you are a mum and have to get a million and one things ready in the morning- this may be perfect for you, as simply it is one less thing to do, and can wait until you have more time to yourself and enjoy your food- this should also ensure you make better food choices- poor choices in food are more common if they are made in a rush or if you are stressed out.

2. It also may be an excellent option for those that travel for work- it means you can have larger meals with clients and colleagues at lunch or in the evening- as you have effectively ‘saved up’ calories, and saves the hassle of having to find something to eat for breakfast – the choices on offer in airports and service stations are typically poor.


· Anyone that has had a difficult relationship with food would likely struggle on this diet, mainly for the reasons mentioned above about those with eating disorders.

· Highly stressed individuals- fasting increases levels of stress hormones, so might prove too much for someone who is naturally that way inclined anyway!

· Some people like breakfast- everyone is different- deprivation can massively impact adherence

· Many overestimate how much food they would usually eat in the day- this is explained below , where I touch on the 5:2 diet.

· Willpower once tired and hungry shoots down-which may result in poor food choices once you do get to eat.

· For Muscle Gain- majority of evidence suggests maximising this requires 4-5 evenly spread doses of protein, so in this case, where you are going to be eating maximum period of 8 hours a day, typically across two meals- this protocol wouldn’t be suitable

· Those working out more than once a day- typically these sessions will be spread out as much as possible, and will need carbohydrates ASAP after each session in order to recover for the next- this wouldn’t be possible if for example the first training session is first thing in the morning, but the person cannot eat until midday.

· Those that need to eat a lot- will be a struggle to get all the calories you need in a small feeding window!

Photo cred: Farmacy

Is the 5:2 diet the way to go?

There are several protocols you can follow, the most well-known being the 5:2 diet, where you eat without restriction for 5 days per week, and only 500-600 calories on the other two. The problem is that it is actually very easy to ‘undo’ the deficit produced in the two days, across the other 5.

In my opinion, if you want to try fasting, the 16:8 diet – fast for 16 hours, with food being consumed in an 8 hour ‘window’- is the protocol I recommend , as the fasting window is not substantial ( for many this would the equivalent of not eating breakfast). I would also advise continuing to track calories ( bearing in mind the calories in vs calories out principle above)

Does it affect performance?

The majority of studies available say no (1)- if you are eating properly during the eating window , your levels of stored carbohydrate should be sufficient to get you through the session. That said, as you get a peak in muscle synthesis and glycogen storage in muscles if you eat post workout, it is advisable to train just before the eating window.

Training fasted might be beneficial in certain circumstances- it is popular with some endurance athletes as body can start using fat for fuel more efficiently and at a higher intensity of work, sparing glucose use until later on in the session , so in theory will be able to keep going for longer , as stored glucose ( known as glycogen) will take longer to run out ( 2).

If you have any questions about this or any other diet protocol ( or anything else!) , please do not hesitate to contact me-I am easily reached via social media (links at the top of the page) or via email ( please visit my contact page)


1. Chaouachi et al (2009) Effects of Ramadan intermittent fasting on sports performance and training: a review . Int J Sports Physiol Perform, 4(4) 419-34.

2. Van Proeyen et al (1985) Beneficial metabolic adaptations due to endurance exercise training in the fasted state. Journal of Applied Physiology, 110 (1) 236-245, doi: 10.1152/japplphysio.00907.2010

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