Intermittent Fasting and Exercise

Article by Jemma Walsh, Blog Editor for Study Active.

Disclaimer – this article will explore the concept of intermittent fasting and exercise by collating views of those that advocate this. The content of the article is not intended as, and should not be interpreted as, nutritional advice.

Introduction to Intermittent Fasting & Exercise

At Study Active we often come across different trends in the sector. From the wired to the wacky we always like to explore these to see what the fuss is all about, and more importantly to see if it’s something that we should (or should not!) be recommending!

In recent months, the combination of intermittent fasting and exercise has gained significant attention especially surrounding claims for its potential to enhance overall health and achieve fitness goals. This dynamic duo, when implemented correctly, is said to lead to numerous benefits, including weight loss, improved metabolic health, and increased strength. But is this safe? Does it work? And is it something that we should recommend? And what exactly is a 16 8 intermittent fasting morning workout? Lets explore all of this further.

Firstly, a little disclaimer - our Study Active trainers are regularly asked about intermittent fasting and working out, its benefits for health, and how it all works. We always explain that intermittent fasting is not part of the qualification syllabus so is not something that our students cover in their course.

See our blog on What nutrition advice a PT should be giving

Further any type of fasting should only be carried out with the supervision of a qualified dietician (sorry PT’s -we are not dieticians so we can’t do this!). However this does not stop us taking a look at what intermittent fasting is and seeing what all the hype is about. Still with me? Lets read on…

What is intermittent fasting?

Well, from my research (which has included desk-based research and speaking with those who advocate this approach) I have found that Intermittent fasting is not a diet; rather, it is an eating pattern that cycles between periods of eating and fasting. The most common approach seems to involve a daily fasting window, this will typically include 16 hours of fasting, followed by an 8-hour eating window. The theory is that, during the fasting period, the body depletes its glycogen stores and begins utilising stored fat for energy. This process, known as ketosis, whilst not part of Government healthy eating guidelines,  is said by its advocates to contribute to weight loss and other health improvements. (Disclaimer – remember we are not advocating or endorsing this, just exploring it!)


How does intermittent fasting Work?

Good question, right? Well form my research, it seems that it’s all about switching to fat-burning mode: When in a fasted state, the body's insulin levels drop, prompting the shift from using glucose for energy, to burning stored fat. This metabolic switch is said to aid in weight loss by tapping into your fat reserves.

Another element to consider seems to be that of cellular repair and something called autophagy (don’t worry, I hadn’t heard of this either!): Fasting is said to trigger autophagy, which is a cellular repair process, where the body removes damaged cells and regenerates new, healthy ones. This process has been linked by its advocates to longevity and a reduced risk of chronic diseases. Though I must make clear, before anyone tries to jump on this bandwagon, this is not routinely recommended by the NHS – so speak to a qualified dietician if you want to explore any possible merits of this.

Another mechanism that keeps coming up is improved insulin sensitivity: Apparently, intermittent fasting has been shown to enhance insulin sensitivity, which is crucial for maintaining stable blood sugar levels. Improved insulin sensitivity can reduce the risk of type 2 diabetes and support overall metabolic health. Again though (without sounding like a broken record) – always consult a qualified Dietician!

What are the Benefits of Intermittent Fasting and Training?

This is the question we are always being asked. There are certainly many claims out there that when working out while intermittent fasting, the synergistic effects can be powerful (or so advocates claim!). So let’s take a deeper dive into this topic and see how intermittent fasting and exercise may complement each other.

  • Enhanced Fat Burning: It is claimed that intermittent fasting while working out can further stimulate fat burning (which is probably why this is such a hot topic!). The theory is that as glycogen stores are already depleted from fasting, the body relies on fat for fuel during exercise, promoting greater fat loss. A popular way to implement this seems to be a 16 8 intermittent fasting period along with morning workout which is claimed to be useful. You may of heard this referred to as the 16 8 intermittent fasting morning workout – now you know what they mean!. Indeed it is said that exercising towards the end of your fasting period (and overnight) may burn higher amounts of fat.
  • Preservation of Lean Muscle Mass: Whilst there is a school of thought that fasting can decrease muscle mass (due to the body eating away at protein as a fuel) intermittent advocate’s suggest that intermittent fasting and weight training when combined, can actually help preserve lean muscle mass. Some advocates even suggest that intermittent fasting and working out can help lose weight while maintaining or building strength at the same time. Always good to multi task I guess!
  • Optimised Hormonal Balance: It is said by some fasting advocates that both fasting and exercise influence hormone levels, such as growth hormone and cortisol, in ways that support muscle growth and fat loss. Due to this, it is claimed that hormonal synergy from intermittent fasting and training can contribute to improved body composition.
  • Increased Energy Expenditure: We all know that exercise burns calories but fasting advocates claim that the calorie deficit will be greater by exercising during a fast. Regular exercising while intermittent fasting is said to increase overall energy expenditure, contributing to such a calorie deficit. This synergy is claimed to be important for weight loss and some even claim that intermittent fasting without exercise will not be as effective in achieving overall fitness goals.

What is the best time to train during fasting?

Whilst we can see the proposed benefits of an intermittent fasting workout, but what time should intermittent fasting and working out be structured and is there a best time to train during a fast? Well according to the Atkins website (remember the Atkins diet?), if you are doing low to moderate intensity exercise then it is best for intermittent fasting exercise to occur towards the end of a fast as this way you would not have to wait long to refuel )as we know refuelling the body after exercise is important to help the muscles recover – see our blog on food for muscle recovery

What are the best exercises to do during fasting?

The Atkins website suggests opting for low intensity exercise during a fast and then save the higher intensities for feeding (as opposed to fasting) periods. Intermittent fasting and weight training may therefore not go so well together if the session is intense, as having some fuel in the tank for this may be of importance.

Some low to moderate intensity exercises that may be popular to do while intermittent fasting could include:

  • Walking – a gentle form of light aerobic exercise which can be done on a treadmill or outside.
  • Cycling – gentle cycling can be done on astatic exercise bike or outside.
  • Swimming – some low intensity swimming can be good aerobic exercise
  • Yoga – if unsure always consult a qualified Yoga professional for advice (such as Study Active’s in-house Yoga expert Chris Walsh!)
  • Pilates – should be with a qualified Pilates professional.

Summary of intermittent fasting & exercise

This has certainly been an insightful journey to understand what people’s views on what intermittent fasting is all about! It certainly seems that there are many fasting advocates out there who suggest that incorporating intermittent fasting and working out with regular exercise can be a useful strategy for achieving optimal health and fitness. We have seen how it is claimed that this combination offers benefits such as weight loss, improved metabolic health, and increased strength. We have also heard how a popular approach to fasting is using a “16 8 intermittent fasting morning workout and general exercise” approach, which fasting individuals claim can unlock their potential for a healthier and more resilient body.

As with any lifestyle change, it's important to consult with healthcare professionals or fitness experts to explore any interventions linked to individual needs and goals, there is a lot of information out there so seeking expert opinions from qualified professionals is always the best way.

We should point out that intermittent fasting is not part of the NHS nutrition guidance and should only be used under the jurisdiction of a qualified health professional such as a Dietician. This article has explored the theories and viewpoints that are prevalent in the sector at present – it must be stressed that this article is not nutrition advice and the views are not necessarily those of anyone at Study Active.

We hope that you have found this article on intermittent fasting and exercise an interesting read – certainly “food for thought”…..or not as the case may be!

Editor’s note

A final word from Study Active’s in house nutrition expert Heather Walker:

“It is acknowledged that intermittent fasting is becoming a popular buzz-term in the sector, however, as Fitness Professionals our remit is to advocate Government Nutrition advice only. This is what we teach on the course, and this is what a Personal Trainer should be adhering to when giving nutrition advice to clients. Anything outside of this, including intermittent fasting, should only be explored under the guidance of a qualified Dietician.”


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