Intermittent Fasting

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Intermittent fasting is trending right now, and I get a lot of questions about it, hence I wanted to share this blog piece about it to help explain it. It is particularly popular in the keto and fitness space for a handful of reasons that i will go into further in the post.


So what is intermittent fasting?

Well naturally, most of us fast everyday (intermittently) without consciously thinking about it. We finish eating around 8/9pm each day, and break fast around 6-9am, meaning we have fasted for about 9-13hrs each day (unless you are getting up during the night and eating or do shift work - split shifts).

To get some of the benefits of intermittent fasting, it usually means fasting for a little longer than this. It’s believed that fasts need to go for at least 12 hours and preferably over 14 hours to get some of the benefits.

Depending on what works for you, you might choose to delay your first meal until 11am or midday, or you might have an early dinner around 5-6pm. This 12-20hr break from eating allows our body time to utilise the energy from the food we’ve eaten and begin to break down stored energy in the form of glycogen from carbohydrates or triglycerides from fat cells. It also means that there is a smaller window of time that you are eating. Hence for people who struggle with over consuming food it might mean that their overall food intake is less, for example 2 meals a day or 3 smaller meals and less snacking.


Some of the types of Intermittent Fasting:


12 hour fast, 12 hour feeding period (e.g. eating between the hours of 7am - 7pm)


16 hour fast, 8 hour feeding period (e.g. eating between the hours of 12pm - 8pm)


20 hour fast, 4 hour feeding period (e.g. eating between the hours of 1pm - 5pm)


5 days of eating whatever you like and 2 days of calorie restriction. 


A day of normal eating followed by a day of fasting (<500cal)


Of course there are many types, you don’t need to follow a strict protocol and you can choose whichever window of time fits in with your lifestyle most. Some of these are more restrictive then others and may make you feel like you are becoming too obsessed with what you are eating. 

Why is it popular in the keto and fitness realms...

I am about to publish along side this blog my 3 week vegan-keto experiment blog part 1 where I go into depth about the keto diet and will explain in more depth why intermittent fasting and the ketogenic diet work synergistically together. To summarise this here, during your fasting period your body will begin to metabolise triglycerides stored in fat cells to produce energy (aka fat burning), hence pro-longing this on a keto diet will mean you are burning additional fat and of course this interests the fitness industry as fasted exercise will mean you burn more fat while working out.

What about your morning coffee? Well, the jury is still out on this one! Some Dr’s believe that even black coffee will break your fast, yet others say a black coffee is fine and so is a dash of milk or fat (MCT oil/Butter). I would definitely steer clear of any sugars and no milky coffees like lattes and cappuccino’s. 

My personal experience...

I have been personally practicing intermittent fasting for the past 9-12 months. I don’t do it 100% of the time as when travelling I often find it really difficult as we are getting up and going out to do activities, not knowing when we will get a chance to have some lunch. However when I am home and in a routine I like to practice 14-16 hour intermittent fasts (~8pm-12pm) as it works for me to break my fast after my workout around 11am or 12pm. I don’t like working out after a meal and I like working out in the mornings so this timeframe works for me. I also don’t find I feel hungry or weak while I am fasted. I do however have a coffee before the gym as a pre-work out supplement (with a dash of unsweetened coconut milk/almond milk/ coconut oil in it for a little bit of energy). After my workout I sometimes have another coffee while I plan out my day of work and then I break my fast around mid-day with a breakfast (usually my 5 Minute Vegan KetoBircher or Balinese Dragon Smoothie- in my cookbook). I personally do believe I feel best when doing this. My digestion feels better, and I feel strong and full of energy. This is totally anecdotal evidence/my opinion and what works for me will not always work for others.


Now lets look at some of the evidence...

There has been some interesting research coming out on the benefits of fasting. Some of which only apply to longer fasts of 1-5 days, however intermittent fasting is gaining popularity as its the easiest kind of fast. One study found Intermittent Fasting caused increased BDNF (brain derived neurotrophic factor) which is involved in serotonin metabolism regulation, synaptic plasticity, improvements in cognitive function and prevention of neuro-aging (Araya et al. 2008: Chung et al., 2002; Fontan-Lozano et al., 2008; Stanek et al., 2008).

Research in animals and humans has uncovered several potentially health-promoting physiologic responses to fasting including ketogenesis, hormone modulation, reduced oxidative stress and inflammation, and increased stress resistance, lipolysis, and autophagy. Clinical research in humans also indicates that fasting improves hypertension, rheumatoid arthritis, cardiovascular disease, metabolic syndrome, osteoarthritis, fibromyalgia, chronic pain, and quality of life. (Finnell et al. 2018). Some of these benefits may only apply to longer fasts (e.g. 1 or more days).

The production of ketone bodies could be involved in improving mood, decreasing pain sensation, and promoting neuro–neuronal protection against hypoglycemia and different types of brain damage (Brown, 2007; Maalouf et al., 2009; White et al., 2007) possibly through anticonvulsant properties (Gasior et al., 2007; Hasebe et al., 2010; Likhodii et al., 2003; Zarnowska et al., 2009). Of course, further studies are needed to determine the role of ketone bodies in neurobiological effects of fasting.

Fasted Mimicking Diet (FMD):

FMD (Fasting Mimicking Diet) is another style of fasting I have just learnt about and find super interesting. FMD is where you fast for 5 days, similar to a water fast however you still eat a calorie restricted and ketogenic diet for the 5 days. This tricks (mimicks) your body into fasting, therefore allowing you to gain more of those longer fast benefits such as neuroprotection, serotonin regulation, improved insulin sensitivity, blood pressure control and autophagy.

I recently learnt about an interesting program developed over in the states by Dr Valter Longo called ProLon. Dr Valter Longo is the Director of both the Longevity Institute at the University of Southern California and The Program on Longevity and Cancer at IFOM in Milan. ProLon is a 5 day plant based FMD, once a month for however many months you would like to do it. It is fully plant based and the meals/snacks are provided to you for the 5 days, providing enough micronutrients and 800cal/day meals to safely do a 5 day fast at home. During the first 1-2 days you begin to improve metabolic health by going into a fasted state where fat cells are metabolised and autophagy begins (which means cells are being cleaned up and recycled) this continues until day 3 where most people are in full ketosis. During the 4th & 5th day stem cells are released (stem cell based rejuvenation) and have been shown to work on cleaning up and repairing damaged cells.

For the purpose of this blog I wont be discussing in any more detail here on longer fasts (e.g. 24hrs to 5 days) however after reading up on some of the research, It's probably going to be something I will try to learn more about, experiment with and share with you information about it in the future.

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What if its not for you?

You are not used to working out fasted, you may feel like you don’t have enough energy.

You start your working day really early and are feeling out of energy early in the day because you haven’t had breakfast yet.

Your work (or workouts) are very high exertion. 

You just don’t feel good going for long periods without food (e.g. low blood pressure or low blood glucose).

Then intermittent fasting may not be suitable to you. Which is totally fine!! It is definitely not the be all and end all of health. Everyone is different and something that works for one person just may not work for another. 

I hope you found this nutrition blog interesting and helpful! I’ve placed my resources below.

Leave a comment below if you have any Q’s or any recommendations for articles and resources for me and my readers to check out.


Elsa, xx

Dietitian & Nutritionist





If you want to learn more about intermittent fasting here are some articles and links.

Blog post - I went vegan-keto for 3 weeks Part 1

Podcast - Rich Roll & Dr Joel Khan

Ketogenic Diet vs Plant Based Diet - 349

Fasting for Longevity - 367

These go for over 2 hours but really really recommend you invest 2 hours into listening to at least one of them.

Netflix - Explained - Can we live forever? (Longevity) 


Finnell et al. BMC Complementary and Alternative Medicine (2018) 18:67 Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting. John S. Finnell1, Bradley C. Saul2, Alan C. Goldhamer3,4 and Toshia R. Myers

Fasted Mimicking Diet

Fasting in mood disorders: neurobiology and effectiveness. A review of the literature.

Water-only fasting and an exclusively plant foods diet in the management of stage IIIa, low-grade follicular lymphoma


*If you suffer from any medical conditions, you should always consult with your practitioner before making any dietary changes.

*Its also important to note that intermittent fasting may not be ideal for people who struggle with disordered eating behaviours and restrictive eating. For example if you are someone who restricts yourself from eating and then ends up binge eating unhealthy foods, following a strict protocol like this may encourage unhealthy habits.*