The concept of fasting is not new. Restricting food intake for certain periods of time has long been practiced by hunter-gatherer populations where food wasn't easily available and fasting has also been associated with various religious practices as well. The practice of fasting is in contrast to the current modern lifestyle of foods that are easily available 24/7. There are many different variations of fasting practices and it has been associated with several health benefits which will be outlined below.
Types Of Fasting
12:12
This is the most common type of fast where you fast for 12 hours. It is typically done through an overnight fast where you finish dinner e.g. at 7.00 p.m. and don't eat again until the next morning e.g. breakfast at 7.00 a.m.
16:8
This is an extension of the 12:12 type of fasting where you fast for 16 hours and eat within an 8-hour window. Again, this can be achieved through an overnight fast and skipping breakfast the next morning where your first meal of the day would be lunch.
Fasting Mimicking Diet (FMD)
The Fasting Mimicking Diet was developed by Dr. Valter Longo. As the name implies, the FMD mimicks a true fast by restricting the number of calories consumed in a day while still obtaining the benefits of a fast. It is typically done through a 5-day cycle initially per month, where the average calories consumed each day is around 800 calories. The FMD program is done through the purchase of specific meal kits that provides meals over the 5 days.
5:2
This approach is similar to the FMD but is less restrictive. In the 5:2 approach, you are able to eat as normal for 5 days of the week, and restrict your caloric intake typically to around 600 calories for the remaining 2 days of the week. A benefit of the 5:2 approach is that the calorie restricted days doesn't have to be done consecutively.
Intermittent Fasting
This is a true fast where you are not consuming any food and only consuming beverages e.g. water-only fast for a period that can range from 1-3 days. This type of fast would be the most challenging in comparison to the other types of fasts listed above.
Potential Applications Of Fasting
Anti-Aging / Longevity
During the period of fasting where there is a restriction in the calories that you are consuming, it induces a process called autophagy where old and damaged cellular components and debris in your body are removed and recycled to make way for new and healthy parts. Think of it as a home renovation or spring cleaning for your body. Research predominantly in animal models have indicated that a dysregulation of autophagy is implicated in the aging process. Therefore, fasting / calorie restriction may be a promising tool that can be used for anti-aging / longevity purposes although more research needs to be done in this area.(1)
Cancer
The practice of fasting has been explored as an adjunct therapy used in conjuction with conventional cancer therapies such as radiation and chemotherapy. During fasting, the body switches from using carbohydrates as its predominant fuel source to using fats. Normal cells can adapt to this change in fuel source but most cancer cells can't adapt as easily, making them more vulnerable to conventional cancer treatments. This has the potential to further increase the effectiveness of conventional cancer treatments. Besides that, fasting also helps to reduce the severity of side-effects commonly experienced with radiation and chemotherapy treatments.(2)
Weight Loss
Traditional approaches to weight loss has been to eat less in order to introduce a caloric energy restriction. This approach may be unsustainable for some people. Recent studies have suggested that various forms of fasting such as time-restricted feeding (e.g. 12:12 and 16:8), 5:2 approach, and intermittent fasting are equally as effective in comparison to the traditional continous calorie restriction approach for weight loss.(3)
Precautions of Fasting
There are several populations for whom fasting is not suitable such as individuals with eating disorders, pregnancy / breastfeeding / children, individuals with moderate to severe stages of adrenal fatigue, and those who are underweight.
How To Get Started
For most people, fasting is generally regarded as a safe practice. A good way to ease into a fasting practice is to ensure that you are sticking to 3 main meals per day and avoid snacking in-between meals. Additionaly, try to have an early dinner so that you will be able to fast overnight until breakfast the next morning using the 12:12 approach. Other variations of fasting that are listed above should ideally be done under the guidance of a healthcare professional; especially if you have any chronic health conditions.
References
1. Chung, K. W., & Chung, H. Y. (2019). The Effects of Calorie Restriction on Autophagy: Role on Aging Intervention. Nutrients, 11(12), 2923. https://doi.org/10.3390/nu11122923
2. Tiwari, S., Sapkota, N., & Han, Z. (2022). Effect of fasting on cancer: A narrative review of scientific evidence. Cancer science, 113(10), 3291–3302. https://doi.org/10.1111/cas.15492
3. Elortegui Pascual, P., Rolands, M. R., Eldridge, A. L., Kassis, A., Mainardi, F., Lê, K. A., Karagounis, L. G., Gut, P., & Varady, K. A. (2023). A meta-analysis comparing the effectiveness of alternate day fasting, the 5:2 diet, and time-restricted eating for weight loss. Obesity (Silver Spring, Md.), 31 Suppl 1(Suppl 1), 9–21. https://doi.org/10.1002/oby.23568