To fast or not to fast

Last update: May 15, 2023
Reading time: 3 minutes
By Brain Matters

What is intermittent fasting?
Fasting has been part of human history for millennia. During our hunter-gatherer ages, we would run into times where food was scarce, we then had to fast till the next successful hunt. Later, fasting became a religious activity, to cleanse the body or increase sobriety. Since the 1800s fasting has been rediscovered to treat a variety of ailments. Nowadays fasting is often used to lose weight quickly. Intermittent fasting is an umbrella term for a group of fasting methods, to give some examples: Time-restricted feeding (TRF) is a fasting method where we go without caloric intake for 12 to 20 hours per day. Other methods are related to reducing caloric intake to a level between 0-25% for consecutive days, for example 5 days of fasting and 2 days of non-fasting (periodic fasting), or to fasting on alternating days (alternating day fasting). 

Studying the effects of fasting
That intermittent fasting (IF) is such a broad concept also makes it difficult to study. Benefits of the different methods may depend on very specific parameters such as duration of the fasting period, amount of restriction etc. Most of our knowledge about intermittent fasting is translated from animal studies. Early studies indicated that the life span of rats could be prolonged by up to 80% when the right caloric restriction (CR) was applied. However, more recent analyses that looked at many CR studies showed that lifespan prolongation might be between 14-45% in rats. However, to what extent this can be translated to humans remains unclear, as even within mice the lifespan prolongation is significantly smaller at 4-27%. Furthermore, animal models indicate that intermittent fasting upregulates a protein called brain-derived neurotrophic factor (BDNF), which is important for neuronal survival and growth.

While data in humans is lacking, there are some findings that showcase benefits of intermittent fasting. Intermittent fasting might be beneficial over caloric restriction, as it yields more benefits for insulin sensitivity. Furthermore, while effects are small to mixed in healthy participants, there might be a bigger benefit in people who are developing neurological disorders. Mild cognitive impairment (MCI) is the stage in between the impairment of a neurological disorder such as dementia and the expected decline from healthy aging. A study in people with MCI revealed that intermittent fasting can lead to broad improvements in metabolism which might modulate cognitive improvements, as the group which underwent IF showed. 

While it’s hard to reveal the mechanisms of each different form of intermittent fasting, there is one overlapping mechanism. The mechanism that triggers while practicing intermittent fasting is a switch in metabolism. Where the body normally extracts its energy from glycogen into glucose, it will now gain energy from stored fat.

Author's note
I was quite skeptical about intermittent fasting before diving into the topic again. I think that people making strong claims without scientific evidence made me more pessimistic about it than I should be, because it seemed too good to be true. Overall, I think it’s a field where further research needs to be done to get a better understanding, at the moment there is too much still unknown. However, the effects in animal studies and the promising findings of human studies are exciting. Who knows, I might even try fasting sometime. 

Author: Kobus Lampe


  • Duregon, E., Pomatto-Watson, L. C., Bernier, M., Price, N. L., & de Cabo, R. (2021). Intermittent fasting: from calories to time restriction. Geroscience43(3), 1083-1092.
  • The article by Gudden et al. (2021) is interesting as it reveals benefits of intermittent fasting in different target groups (such as neurological disorders).
  • Gudden, J., Arias Vasquez, A., & Bloemendaal, M. (2021). The effects of intermittent fasting on brain and cognitive function. Nutrients13(9), 3166.
  • Harding, S. (2021). Intermittent Fasting: Clinical Considerations. The Journal for Nurse Practitioners17(5), 545-548.
  • Ooi, T. C., Meramat, A., Rajab, N. F., Shahar, S., Ismail, I. S., Azam, A. A., & Sharif, R. (2020). Intermittent fasting enhanced the cognitive function in older adults with mild cognitive impairment by inducing biochemical and metabolic changes: a 3-year progressive study. Nutrients12(9), 2644.
  • Seidler, K., & Barrow, M. (2022). Intermittent fasting and cognitive performance–Targeting BDNF as potential strategy to optimise brain health. Frontiers in Neuroendocrinology65, 100971.
  • Xu, S., Jiang, Y., Zhang, Y., Xu, W., Zhang, H., Yan, Q., ... & Shang, L. (2022). Dietary recommendations for fasting days in an alternate-day intermittent fasting pattern: a randomized controlled trial. Nutrition, 111735.
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