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Beyond Tradition: The Science of Intermittent Fasting for Longevity and Health

Photo by Viktoria Slowikowska

What is Fasting?

Put simply, “fasting means a restriction of the intake of solid foods” (Wang & Wu, 2022).

Globally there are numerous iterations of intermittent fasting practices, predominantly rooted in established ancestral, sociological, or theological frameworks (Michalsen, 2010). For example, fasting during Ramadan involves a time-restricted intake of food and drink for religious purposes, which can be compared to intermittent fasting (Sydor & Engin, et al., 2024).

Types of Fasting

The application of intermittent fasting has extended beyond purely religious observance and has become a popular intervention to promote health.

Intermittent fasting requires the subjects not to consume any calorie-containing food during the fasting period. “Intermittent” highlights the characteristics of an alternating fasting time (Wang & Wu, 2022).

Intermittent fasting can include:

  • Alternate-day fasting: the fasting day and the feeding day alternate each day. The caloric intake on the fasting day is 25% of the daily caloric intake (approximately 2090 kJ), and the subjects can eat freely on the feeding day (Trepanowski & Kroeger et al. 2017).
  • Time-restricted feeding: involves fasting for a specified time each day and eating freely during the rest of the time. Common time allocation methods are 16/8 (16 h fasting, 8 h free eating), 18/6 (18 h fasting, 6 h free eating), and 20/4 (20 h fast, 4 h free eating) (Malinowski & Zalewska et al., 2019).
  • Whole-day fasting: fasting for 24 hours, usually from the time of waking until same time the following morning.
  • Modified fasting methods: involves fasting on specific days each week; the intake of calories on the designated day is only approximately 1672~2508 kJ, and free eating occurs during the rest of the week. Specific examples include the 5 : 2 (2 days of limited calorie intake) and 4 : 3 (3 days of limited calorie intake) diet plans (Malinowski & Zalewska et al., 2019).

Dry Fasting vs Water Fasting

“Ramadan fasting is a special type of time-restricted feeding; during Ramadan, people are not allowed to eat, drink, smoke or take medication during the daytime but are allowed to eat or drink from sunset until dawn [5, 6]. ” (Wang & Wu, 2022).

“Compared with the Mediterranean diet or continuous caloric restriction (CR), IF does not restrict calorie intake during the ad libitum period, so it has better compliance and tolerance. This article demonstrates the effects of fasting on human metabolism and psychological health.” (Wang & Wu, 2022).

References

Wang Y, Wu R. The Effect of Fasting on Human Metabolism and Psychological Health. Dis Markers. 2022 Jan 5;2022:5653739. doi: 10.1155/2022/5653739. PMID: 35035610; PMCID: PMC8754590. Retrieved at: https://pmc.ncbi.nlm.nih.gov/articles/PMC8754590/

Michalsen, A. Prolonged Fasting as a Method of Mood Enhancement in Chronic Pain Syndromes: A Review of Clinical Evidence and Mechanisms. Curr Pain Headache Rep 14, 80–87 (2010). https://doi.org/10.1007/s11916-010-0104-z Retrieved at: https://link.springer.com/article/10.1007/s11916-010-0104-z

Svenja Sydor, Ender Engin, Samantha Wittek, Peter Lemmer, Jan Best, Martin Steinmetz, Anja Figge, Andreas Jähnert, Mustafa Özcürümez, Martina Broecker-Preuss, Wing-Kin Syn, Ali Canbay, Paul Manka,
Religious intermittent fasting: Effects on liver health, metabolic markers, and gut microbiota in type 2 diabetes patients, Clinical Nutrition Open Science, Volume 58, 2024, Pages 370-383, ISSN 2667-2685, https://doi.org/10.1016/j.nutos.2024.11.001. Retrieved at: https://www.sciencedirect.com/science/article/pii/S266726852400113X

Trepanowski J. F., Kroeger C. M., Barnosky A., et al. Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese Adults. JAMA Internal Medicine . 2017;177(7):930–938. doi: 10.1001/jamainternmed.2017.0936. Retrieved at: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2623528

Malinowski, B., Zalewska, K., Węsierska, A., Sokołowska, M. M., Socha, M., Liczner, G., Pawlak-Osińska, K., & Wiciński, M. (2019). Intermittent Fasting in Cardiovascular Disorders—An Overview. Nutrients, 11(3), 673. https://doi.org/10.3390/nu11030673 Retrieved at: https://www.mdpi.com/2072-6643/11/3/673