Fasting can stimulate the immune system and help to fight infections. At the same time, it reduces chronic inflammation, which increases the risk of many conditions, such as heart disease, diabetes, and cancer.
One of the main reasons why people fast is weight loss. However, an additional potential benefit of most fasting practices is its stimulation of the immune system. In addition, fasting can lead to improvements in health conditions such as obesity, diabetes, cardiovascular disease, cancers and neurological disorders.
When fasting, our cells start a recycling process, which also takes place in the white blood cells (lymphocytes, a key component of the immune system). During this process, the body breaks down some immune fighting white blood cells.
During the periods of non-eating, our white blood cell count is reduced, which in turn stimulates the immune system to begin producing new white blood cells (1). The body instinctively knows to start saving energy and one way it does this is by killing off old or damaged immune cells. Once eating starts up again, the immune system jumps into high gear to replenish the cells that were recycled.
Some cells in the body support the immune response by attacking invading pathogens. They leave the bloodstream during fasting when nutrients get low.
They migrate to bone marrow, which is full of nutrients. They can regenerate there and can then better protect the body from infection (2).
While the initial depletion of white cells may take 24-48 hours to set off, it seems that it is only necessary to do this once or twice a year to rip the benefits of this process. It is likely that similar benefits can be obtained with shorter forms of fasting, such as 16/8 fasting.
An increasing body of evidence proposes that eating in a 6-hour period and fasting for 18 hours may trigger a metabolic switch from glucose-based to ketone-based energy, with augmented resistance to stress, greater longevity, and lower incidence of chronic diseases, such as cancer and obesity.
Intermittent fasting periods do more than burn fat. Intermittent fasting can reduce inflammation in the body (3). This should have benefits against aging and development of numerous diseases. Chronic inflammation has been linked to numerous negative health conditions such as heart disease, diabetes, and certain types of cancer (4). Over time, chronic inflammation can trigger the immune system to attack healthy tissue and organs in the body. Because intermittent fasting reduces inflammation, it may also improve symptoms of arthritis and even rheumatoid arthritis (5).
A key benefit of fasting is autophagy, meaning the recycling of the old, damaged, molecules within the cell.
An autophagy-related process, called xenophagy, helps to break-down pathogens within the cell. Because fasting promotes autophagy the cell already has everything on hand to destroy pathogens (6).
Apart from a reduction in energy intake, it is important to remember that when we fast we are also (ideally) leaving out additional triggers that may not be so beneficial for health, including sugars, highly processed foods, and alcohol. While these may not represent a problem when consumed in moderation, if they are regularly taken in in large amounts they promote damaging processes in our bodies such as inflammation and oxidative stress with all of their corresponding effects.
Fasting may give the immune system a boost, especially if this practice is supported with healthy and balanced choices when breaking the fast. However, it is important to keep in mind that fasting may have different effects on different people. Informing your healthcare professional that you wish to pursue a fasting practice is as important as finding a form of fasting that works for you.
1. Cheng CW, Adams GB, Perin L, et al. Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression. Cell Stem Cell. Jun 5 2014;14(6):810-23. doi:10.1016/j.stem.2014.04.014
2. Nagai M, Noguchi R, Takahashi D, et al. Fasting-Refeeding Impacts Immune Cell Dynamics and Mucosal Immune Responses. Cell. Aug 22 2019;178(5):1072-1087 e14. doi:10.1016/j.cell.2019.07.047
3. Faris MA, Kacimi S, Al-Kurd RA, et al. Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects. Nutr Res. Dec 2012;32(12):947-55. doi:10.1016/j.nutres.2012.06.021
4. Pahwa R, Goyal A, Bansal P, Jialal I. Chronic Inflammation. StatPearls. 2021.
5. Venetsanopoulou AI, Voulgari PV, Drosos AA. Fasting mimicking diets: A literature review of their impact on inflammatory arthritis. Mediterr J Rheumatol. Dec 2019;30(4):201-206. doi:10.31138/mjr.30.4.201
6. Kim HJ, Lee S, Jung JU. When autophagy meets viruses: a double-edged sword with functions in defense and offense. Semin Immunopathol. Dec 2010;32(4):323-41. doi:10.1007/s00281-010-0226-8
Brushing teeth while fasting will not break the fast. Combined with intermittent fasting, brushing will improve oral health and hygiene.
Eating at the end of your fast is something you've been waiting for, here is how you can do it the right way.