TOPIC REVIEW….Fasting and Performance
What are the various approaches to intermittent fasting?
There are many different approaches to intermittent fasting all of which are divided into three categories:
- Intermittent calorie restriction (ICR)
- Alternate Day Fasting ADF)
- Time Restricted Feeding (TRF)
ICR includes the 5:2 and the FAST 800 approaches:
- 5:2 where you eat 500-600 calories on 2 days a week and eat to normal energy requirements on the other 5 days
- FAST 800 – where you eat 800 calories every day for up to 12 weeks until ideal body composition is reached
ADF is when one day you eat to normal Energy requirements and the next day eat 25% of energy requirements only. For example 2000 calories vs 500 calories
TRF is when you fast during a set number of hours each day and eat during the remainder of daily hours. For example 14.10 16:8 or 18:6 or 20:4 – 16:8 possibly being the easiest to implement
What are the PROs and Drawbacks of Intermittent Fasting?
There are potentially many PROs and possible drawbacks to intermittent fasting. The choice is very individual and this approach to eating may not be suitable for everyone, especially endurance runners.
Positive aspects of Intermittent Fasting:
- Promotes weight loss and supports optimal body composition
- Helps improve energy
- More efficient recovery from training
- Trains the body to switch from glucose use to utilising fat as fuel – supportive on long endurance runs
Potential Drawbacks of Intermittent Fasting:
- May lead to STRESS and LOW BLOOD sugar levels, which could have a knock-on effect on cortisol levels
- Cortisol manages energy by supporting blood sugar balance. If no food has been eaten for several hours and blood sugar drops too low the adrenal glands produce cortisol to signal production of glucose to bring blood sugar balance back into balance
- Following an overnight fast blood sugar levels, in some people, may be TOO low. This could lead to cortisol being activated to bring glucose form the body’s store to help provide energy and balance blood sugar
- Sometimes this can lead to overall cortisol levels being higher than they need to be (or should be) during the day. This can have a further knock-on effect on other hormones including sex hormones, neurotransmitters etc
FEMALE FACTORS – see below
What is the Current Research Saying About Fasting for Sports Performance?
There hasn’t been very much new data released since early 2020, however some factors worth mentioning include:
Exercising in a fasted-state (which is generally following an overnight fast and before eating the first meal of the day) allows higher levels of fat oxidation (so using fat as fuel) BUT this is only beneficial during exercise performed at low-to-moderate intensity. Overtime, exercising in the fasted-state could help increase the relative intensity at which maximal fat oxidation occurs.
5’AMP-activated protein kinase (AMPK), which is a compound that acts as an energy sensor at cellular level, regulates cellular and whole-body energy balance and is activated during exercise. Activation of AMPK can lead to a range of metabolic adaptations including:
- Increases in glucose uptake
- Fat oxidation
- Mitochondrial biogenesis – so more mitochondria being synthesized – they are our energy powerhouses – so vital for runners
Some studies have shown that FASTED-state running results in greater increases in the activity of AMPK (following a 1h steady-state endurance exercise session at 65–70% VO2max). Studies have also noted that exercise performed with “normal” muscle glycogen levels plus additional CHO intake has a blunting effect on AMPK activity – in other words, AMPK is less effective. These effects appear to occur during low-moderate exercise levels only and performed for 90mins or less.
Tips on Including Fasting in YOUR Daily Life and Running Training
- To get the best outcome make some compromises will need to be made. For instance; will you build your food timings around your run training or vice versa? Something to consider
- Consider starting with TRF first – this may be the best approach to support a running training schedule
- Possibly complete your run following an overnight fast then delay breakfast (following the 14:10 approach). This may encourage the use of fat as fuel and efficient AMPK activity both of which could help with optimal body composition, sparing glycogen and increasing mitochondria production
- Get everyday nutrition optimal CONSISTENTLY before fasting – aim for healthy good quality food and plate balance (reduce carb portion if you are wanting WL) plus good hydration and limit stimulants like caffeine and limit alcohol/soft drinks
- If required or if you think it may suit your lifestyle better, add Calorie Restrictions or Alternate Day Fasting once you have adjusted to this new way of eating
- Start slowly and make adaptations/adjustments – you don’t have to do everything at once. As with everything you have to practice