Fasting has been around for centuries, and was no doubt a normal state of affairs for our ancestors. Without grocery stores, restaurants and convenience shops, or with the structured routine of schedules and lunch breaks – they would have gone for long periods of time between meals, and even days with very little food. But does this mean that intermittent fasting (IF) is right for everyone?
The most commonly practiced IF today is time restricted eating – usually something like 16/8 – where you eat within an 8 hour window, then consume zero calories for 16 hours.
Most people do this by “skipping” breakfast – though in reality it not skipping breakfast, it is just delaying it. (breaking the fast later in the day!)
For other options for IF are outlined here in this great article:
www.healthline.com/nutrition/6-way-to-do-intermittent-fasting
What are the benefits for 16 hour fasting?
- Improved blood sugar control: In a fasted state, your cells will switch from using glucose as the primary source of energy to using fat. The advantage of this is that your body can learn to switch between the two and allow even energy levels – without “crashes’ from insulin spikes and low blood sugar often seen people who rely on processed sugar all day or run on adrenalin and cortisol (stress hormones). Please note that that is does not work for everyone, as I will explain below.
- Enhanced longevity and delay aging– there is some evidence in animal studies to suggest that fasting can increase your lifespan
- Increased weight loss and fat loss – this is due to a calorie deficit that is achieved by limiting the times you eat. There is no “magic” for weight loss, it occurs due to calorie deficit no matter which diet you follow.
There may be other benefits to fasting such as increased production of growth hormone, reduced inflammation, enhanced heart health, prevention of neurodegenerative disorders. However, most of these are only seen in very small studies, animal studies, and for prolonged fasting of 24+hrs or more.
What are the disadvantages?
- Elevated cortisol levels. If a person has underlying cortisol dysregulation (which is very common in people who have very busy schedules, high levels of stress, or hormone imbalances) the increase in cortisol due to fasting can lead to elevated blood sugar. This in turn leads to an insulin spike, subsequent blood sugar drop, then encourages even more cortisol to be produced to manage the state of stress that the body feels. Regulation of cortisol is paramount for athletes.
- Decreased insulin sensitivity for women. Many studies have shown that women do not respond as well to IF as men. In one study, after practicing fasting for 3 weeks, the women’s glucose response to a meal worsened, whereas for men it improved insulin sensitivity. A further complicating factor to consider in women is the fluctuating hormones estrogen and progesterone. Both hormones impact the bodies response to glucose. Calorie restriction (such as fasting) can lead to changes in the monthly menstrual cycle. Please note that a regular cycle is not only important for fertility, but also important for bone health, and long term thyroid and metabolic health.
A better option for women would be to adopt a 12 hour fasting cycle – say 7pm to 7am. This is something that I often recommend to my female clients. It is a great way to cut out the post dinner snacks, but it doesn’t compromise exercise recovery or hormone regulation.
Conclusion:
16/8 Time restricted eating has some significant benefits: weight loss, improved blood sugar control and delayed ageing – awesome !! … more years to keep on running
however… it is NOT for everyone.
If any of these apply to you, then IF is most likely not going to be of benefit
- Highly stressed and/or not getting enough sleep
- Underweight or a very lean female
- Already insulin resistant or have blood sugar regulation/cortisol issues
- Have hormonal imbalances, a thyroid condition or missing monthly menstrual cycle
What about for fat adaption or metabolic efficiency for running? I thought fasting helped with this?
Yes it is true that fasting can help with teaching your body to utilise fat more efficiently during endurance exercise. The key benefit of this is that you do not need to take on board as much fuel (carbohydrates) during endurance exercise without the risk on “bonking” or complete glycogen depletion. This can be useful if you are someone who suffers from tummy upsets during training and events. It is very useful for people who are undertaking multi-day events.
Please note that utilising fats more efficiently does not have any relationship to improved performance (ie speed) in fact the opposite is true – the more you can teach your body to absorb carbohydrates during endurance exercise the faster you will be able to go.
If you would like to learn more about what is suitable for you, I am available for personal appointments, you can book online.
