Intermittent Fasting – Is It Right For You?


Intermittent fasting – a topical and somewhat controversial lifestyle choice embraced by many big name CrossFitters in recent months. (Rich Froning to name one) So, what’s the big deal? What is fact and what is fiction? We’ve partnered with Liam Holmes, performance nutritionist and owner of pH Nutrition to bring you a comprehensive guide on the topic. Liam has worked in elite sport for 12 years and now coaches CrossFit games athletes, beginners and everyone in between, alongside his nutrition business.

Scroll down to get clued up and get to grips with what’s myth and what’s science.

Intermittent fasting (IF) is a pattern of eating that alternates between predetermined times of fasting and feeding. 


It doesn’t specify which foods you should eat but rather when you should eat them. 

The reason it has become more and more popular is due to the proposed weight loss, longevity, increased concentration levels and lowered inflammation. 

With it becoming a tool that some athletes are now implementing the question is should you start following intermittent fasting? 

Firstly, let’s just cover a few of the basics.

There are numerous different protocols, but these are the most popular:

  • The 16/8 method: Also called the Leangains protocol, it involves skipping breakfast and restricting your daily eating period to 8 hours, such as 12-8pm. You then you fast for 16 hours in between.
  • The 5:2 diet: With this method, you consume only 500–600 calories on two non-consecutive days of the week, but eat normally the other 5 days.
  • Eat-Stop-Eat: This involves fasting for 24 hours, once or twice a week, for example by not eating from dinner one day until dinner the next day.


Why fast?

When you fast, several physiological things happen in your body. Hormone levels are altered and cells initiate important repair processes and can change the expression of certain genes.

Here are some changes that occur in your body when you fast: 

  • Human Growth Hormone (HGH): The levels of growth hormone can increase. This is one of the leading reasons people fast as it aids muscle retention and fat loss.
  • Insulin drops, thus improving insulin sensitivity. Lower insulin levels can make stored body fat more accessible.
  • When fasted, your cells initiate cellular repair processes (the main being autophagy), and aid the bodies own antioxidant systems. This can help lower overall inflammation in the body.
  • Gene expression: There are changes in the function of genes related to longevity and protection against disease  

What you have to be very wary of is that these things do not happen in isolation. For example, insulin sensitivity may be improved during the fast but it doesn’t automatically equate to weight loss! 

Some of the main reasons people use fasting are for -

  • Weight loss - it is a method that allows you to get in a calorie deficit and as there less restriction on what you can eat, it can help to increase compliance. 
  • Lowered inflammation - less chronic inflammation in the body is always a positive thing! Great for health and for improving recovery from exercise.
  • Brain health - Intermittent fasting increases the brain hormone BDNF and may aid the growth of new nerve cells. Anecdotal evidence, my clients feel more switched on and focused during periods of fasting.
  • Gut health. Simply allowing more time between meals can lower the stress on the gut that is placed on it by snacking, poor food choices and excess calorie intake.
  • Improving hormone levels. As I mentioned earlier, HGH can be increased and there is some evidence that it can help increase testosterone levels (don't take what you see on YouTube as gospel). 

Fasting is one part of the jigsaw. Saying that it improves one specific area in isolation has no real practical application. Be very wary of people saying “if you fast you will definitely [insert your goal] ”

Common issues I see with people fasting

Fasting can be challenging to do, and I encourage anyway thinking about doing it to slowly build-up to the protocol you are following. If you fast for 15 hours that is fine, do not think you have to dive straight in and get things 100%.

There are a few common issues that the research and my own anecdotal experience have identified: 

  • Unhealthy approach to food - used as a way to offset poor diet choices
  • Reliance on coffee
  • Reduction in athletic performance
  • Frequent diarrhoea
  • Binge eating during the feeding window
  • Some women who try Intermittent Fasting claim to experience missed periods, metabolic disturbances and early-onset menopause. Women’s reproductive hormones are highly sensitive to energy intake.

Fasting and training

Here’s the key: IF isn’t all about eating less, but rather eating within a specific time window. With one of the key determinants of athletic performance being energy availability, it doesn't matter if you fast or not, if you are not eating enough to fuel the volume and intensity of your training you won’t be maximising your performance.

But what about fasted training improving aerobic capacity?

Exercising in a fasted state forces the body to use its energy systems more efficiently. Fat oxidation increases following a fasted workout (i.e. an easy aerobic exercise session done first-thing in the morning following an 8-12 hour overnight fast). 

Essentially, fasting helps your body become better at metabolising fat rather than relying on the carbohydrates that are readily available in a non-fasted state. So it could provide benefits in sports where being efficient using fats is an advantage (running, triathlons etc)

So what about CrossFit? 

The issue I see with Intermittent fasting and people who train regularly is it causing low energy availability, resulting in a reduction in performance. 

If done correctly then it is absolutely fine!

CrossFit is predominantly fuelled by the ATP-PC and A-lactic energy systems, meaning that carbohydrates are the main fuel source. However, there is still a requirement for people to have a good level of aerobic fitness. 

Fasting (or training in a fasted state) can help improve the mechanisms required for aerobic energy production. 

There is also a huge body weight element to CrossFit so having a good power to weight ratio is beneficial. Fasting is a method that can help people lose weight, resulting in an improvement in performance.

** Liam’s tip - people that do CrossFit / HIIT training early in the morning - using the 16/8 protocol where you fast until lunchtime often results in compromised recovery and a drop in performance. I would suggest to only use on rest days or maybe during a de-load week **

Final thoughts 

Do not think that you need to do IF 100% or not at all. It is a method that can be used at specific times. 

Make sure that your feeding is structured. Ensure you are eating enough to fuel your training and work towards your goal.

Do not think you can eat whatever you want. Calories and food quality still matter!

Personally, I use it once or twice a week when I am resting, sleep in a little later and have a lower output that day. I encourage you to try it, be aware of how you feel and make small changes to find a way of doing it that works for you.