Intermittent Fasting (IF) has gained significant attention in recent years as a lifestyle approach that involves cycles of fasting and eating. IF is promoted for longevity (human studies are lacking), weight loss, diabetes remission, improved cardiovascular markers, and as part of cancer treatment. Let’s learn about the reported benefits, different protocols, and the existing evidence supporting its metabolic effects.
What is Intermittent Fasting?
Intermittent Fasting is a type of calorie restriction that involves abstaining or significantly restricting food intake for a set period of time.
Intermittent Fasting – Eating Patterns
While there are many alterations of IF, the following protocols are the most common:
Alternate Day Fasting (ADF)
Eating every other day. Alternating between fasting days (no calories are consumed), and “feasting” days (no calorie restriction).
Alternate Day Modified Fasting (ADMF) (5:2 Diet)
Consuming 500-600 calories (20-25% of regular calorie intake) two days a week and eating normally on other days.
Time-Restricted Feeding (Time-Restricted Fasting)
Restricts food intake to specific periods of the day, typically between 8 to 12 hours a day. E.g. if you eat all your meals between 10 am and 6 pm, your feeding window is 8 hours, and your fasting window is 16 hours.
What is the Idea behind Intermittent Fasting?
Reduced calorie intake will induce ketosis and potentiate weight loss. - Not necessarily.
During fasting, the body undergoes metabolic switching from glucose to fatty acid-derived ketones, tapping into fat stores for energy. The body switches to ketosis (starts using fat for energy) around day 2 or 3. That means that while this is true for prolonged fasts, it is not always true for IF. Why? Because IF does not typically last longer than two days.
IF will potentiate Autophagy and that will lead to DNA repair. - Not necessarily.
Autophagy (“self-eating”) is the body’s way of cleaning old or damaged cellular components and maintains cellular homeostasis. Just like ketosis, autophagy begins when glucose and insulin levels drop considerably, after about 24 hours of fasting, peaking at around 48 hours of fasting. While IF is often linked to autophagy, it's essential to note that other methods, such as exercise, quality sleep, exposure to hot temperatures, acupuncture, and consuming certain foods (e.g. coffee, green tea, broccoli etc.) can also induce autophagy.
IF as a strategy for increasing chemotherapy effectiveness and tolerability in cancer treatment. - True.
Several studies have shown that IF throughout chemotherapy was well tolerated and decreased the toxicity of chemotherapy.
Sample Intermittent Fasting Menu: 5:2 Diet
5 days a week - no food restrictions
2 days a week - 500–600 calories
Total calorie intake per day: 525
Breakfast: 1 cup cooked oats with banana (255 calories)
Lunch: 1 small bowl of veggie soup (170 calories)
Dinner: 1 cup of grapes (100 calories)
What are the effects of Intermittent Fasting on Health, Aging, and Disease?
“It is crucial to note that the long-term sustainability of IF and its applicability to diverse age groups remain uncertain. Clinical studies have predominantly focused on overweight young and middle-aged adults, limiting the generalization of observed benefits and safety.”
In conclusion...
The main benefit of IF lies in cancer treatment, potentiating chemotherapy. However, it may not be justified for everyone unless an individual prefers a short eating window. Sustainability remains a concern for most people, as IF can interfere with normal life, social events, and daily activities. The reported benefits, such as calorie reduction and weight loss, can be achieved through alternative means.
Since IF does not prescribe or restrict specific foods, but rather emphasizes when to eat, a healthier strategy would be to fast for 12 to 16 hours a day and then eat a health-promoting diet. This way the purported benefits of IF would be more pronounced, and our social life would not be negatively impacted.
References:
Omar EM, Omran GA, Mustafa MF, El-Khodary NM. Intermittent fasting during adjuvant chemotherapy may promote differential stress resistance in breast cancer patients. J Egypt Natl Canc Inst. 2022;34(1):38. Published 2022 Sep 12. doi:10.1186/s43046-022-00141-4
de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease [published correction appears in N Engl J Med. 2020 Jan 16;382(3):298] [published correction appears in N Engl J Med. 2020 Mar 5;382(10):978]. N Engl J Med. 2019;381(26):2541-2551. doi:10.1056/NEJMra1905136
Omar EM, Omran GA, Mustafa MF, El-Khodary NM. Intermittent fasting during adjuvant chemotherapy may promote differential stress resistance in breast cancer patients. J Egypt Natl Canc Inst. 2022;34(1):38. Published 2022 Sep 12. doi:10.1186/s43046-022-00141-4
Tiwari S, Sapkota N, Han Z. Effect of fasting on cancer: A narrative review of scientific evidence. Cancer Sci. 2022;113(10):3291-3302. doi:10.1111/cas.15492
Zhou J, Farah BL, Sinha RA, et al. Epigallocatechin-3-gallate (EGCG), a green tea polyphenol, stimulates hepatic autophagy and lipid clearance [published correction appears in PLoS One. 2014;9(5):e96884]. PLoS One. 2014;9(1):e87161. Published 2014 Jan 29. doi:10.1371/journal.pone.0087161
Herman-Antosiewicz A, Johnson DE, Singh SV. Sulforaphane causes autophagy to inhibit release of cytochrome C and apoptosis in human prostate cancer cells. Cancer Res. 2006;66(11):5828-5835. doi:10.1158/0008-5472.CAN-06-0139
Tian T, Sun Y, Wu H, et al. Acupuncture promotes mTOR-independent autophagic clearance of aggregation-prone proteins in mouse brain. Sci Rep. 2016;6:19714. Published 2016 Jan 21. doi:10.1038/srep19714
Zhang M, Jiang M, Bi Y, Zhu H, Zhou Z, Sha J. Autophagy and apoptosis act as partners to induce germ cell death after heat stress in mice. PLoS One. 2012;7(7):e41412. doi:10.1371/journal.pone.0041412