This article presents several human studies that show that exercise promotes autophagy independent of intermittent fasting.
Autophagy is when the body recycles old, dysfunctional, precancerous, and previously damaged cells to make new proteins.
After exercise, autophagy replaces damaged skeletal muscle cells during strenuous physical activity. That facilitates muscle adaptation to that exercise, whether it is weight lifting or endurance training.
The past years have shown interest in autophagy due to its other health benefits. It improves cardiovascular health, prevents muscle loss, limits intraabdominal adhesions, strengthens the immune system to counter infections like COVID-19, and has utility in Post -COVID-19 vaccine syndrome.
I only included human studies because autophagy processes are different in humans compared to animals. [4]
Interestingly, not all research shows that intermittent fasting is necessary for autophagy.
Exercise without fasting induces autophagy
Møller and colleagues conducted a cross-over study where a group of men exercised for 60 minutes after fasting for 36 hours. One month after, the same group performed the same exercise in a non-fasting mode.
After the exercises, skeletal muscle biopsies were obtained to look for proteins that initiate autophagy. (Unc-51 like autophagy activating kinase (ULK1) and Adenosine 5′ monophosphate-activated protein kinase (AMPK).
The result showed that autophagy is activated in human skeletal muscle after 60 minutes of exercise, whether they fasted or not. [1]
The study showed that 36 hours of fasting did not add to the increase in the level of AMPK induced by fasting.
In another experiment, Brandt et al. had two groups of men matched in physical fitness perform two sets of exercises differing in intensity for eight weeks.
One group performed at moderate intensity and the other at a higher intensity. No group fasted in this study.
Both groups’ autophagy markers (AMPK and ULK) were elevated immediately after exercise.
They concluded that exercise increases autophagy markers in human skeletal muscle within the first two hours of recovery. Additionally, eight weeks of exercise training increases autophagy and mitophagy regulation capacity in moderate and high-intensity exercises.[2]
Mitophagy is the autophagy of the mitochondria. Essentially, the old dysfunctional mitochondria are replaced with brand new ones. Well-functioning mitochondria use glucose better, improve insulin resistance and prevent oxidative stress by reducing free radical formations.
Mitophagy also happens in intermittent fasting.
Effect of fasting on autophagy in trained and untrained groups
The third study examined the impact of 36-hour fasting on trained and untrained men. The two groups were differentiated into trained and untrained using parameters from their muscle biopsies.* No exercise was done during the experiment.
Both groups fasted for 36 hours. After the fast, they had a standardized meal (42% carbohydrate, 12% protein, and 46% fat). Next, muscle biopsies were obtained at 2, 12, 24, and 36 hours.
The study showed that both trained and untrained have increased in the markers for autophagy, but only the trained showed autophagy initiation in their muscles.
This shows that exercise is necessary for autophagy to happen when doing intermittent fasting.
In summary, the three studies show that exercise can induce autophagy. And for people who do intermittent fasting, adding physical activity can boost autophagy.
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*The trained and untrained subjects in the third study were differentiated using the following parameters in their muscle biopsies. (maximum oxygen uptake, muscle citrate synthase activity, and oxidative phosphorylation protein level)
Related:
- Exercise alone can induce autophagy
- Intermittent fasting for Post COVID Vaccine Syndrome: Autophagy
- Autophagy – How to Recycle Yourself
- The 20/80 Rule for Health
- No Time to Exercise? Let’s Fix That.
References:
- Møller AB, Vendelbo MH, Christensen B, Clasen BF, Bak AM, Jørgensen JO, Møller N, Jessen N. Physical exercise increases autophagic signaling through ULK1 in human skeletal muscle. J Appl Physiol (1985). 2015 Apr 15;118(8):971-9. doi: 10.1152/japplphysiol.01116.2014. Epub 2015 Feb 12. PMID: 25678702.
- , , , . Exercise and exercise training-induced increase of autophagy markers in human skeletal muscle. Physiol Rep, 6 ( 7), 2018, e13651, https://doi.org/10.14814/phy2.13651
- Dethlefsen MM, Bertholdt L, Gudiksen A, Stankiewicz T, Bangsbo J, van Hall G, Plomgaard P, Pilegaard H. Training state and skeletal muscle autophagy in response to 36 h of fasting. J Appl Physiol (1985). 2018 Nov 1;125(5):1609-1619. doi: 10.1152/japplphysiol.01146.2017. Epub 2018 Aug 30. PMID: 30161009.
- Sanchez, A.M.J. (2016), Autophagy regulation in human skeletal muscle during exercise. J Physiol, 594: 5053-5054. https://doi.org/10.1113/JP272993
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