You may have been hearing a lot about intermittent fasting and its potential health benefits over the last few years. If you have been wondering what it is and if it can indeed boost your immune system, you are in the right place. In this blog post, we will outline what intermittent fasting entails, what metabolic effects it has and if fasting is good for your immune system.
What is intermittent fasting?
Intermittent fasting is when food intake is restricted during certain time intervals, while resuming standard intake during other times. Common methods include fasting on alternate days, consuming all food in a short period of time of the day or fasting two times per week (1). There are several studies indicating that fasting regimens can help prolong lifespan, and have therefore become topics of intense conversation.
What effects does intermittent fasting have on my body?
In order to walk, run, eat, think or even leisurely sit on the couch and sleep, we require energy. This energy is derived from from food intake, which is then converted into usable buckets of energy inside our bodies. In humans and other mammals, there are different ways of harnessing this energy, through several interconnected metabolic channels. Fasting results in a metabolic switch from using glucose (sugar) in circulation or breaking down sugar stores, to using ketone bodies for energy (2).
Wait a minute, what are ketone bodies? Ketone bodies are molecules produced from fatty acids in the liver (including acetone, which gives nail polish remover its distinctive smell) (3). The ketone bodies are then delivered throughout the body as an alternative energy source to sugars. Ketone bodies can contribute up to 20 % of energy expenditure during periods of fasting, while they only make up 5 % of energy usage during fed periods (4). Utilisation of ketone bodies as an energy source also occurs after exercise, during pregnancy and following a low-carbohydrate diet (which you may have heard of as a ketogenic diet). Therefore, fasting results in the enhanced production and use of ketone bodies as an energy source, as opposed to the use of sugars.
What are some fasting routines?
Intermittent fasting can be undertaken in a number of ways, and we are providing the details of three of these (Table 1). These fasting routines have been shown to extend lifespan in animals, accelerate and promote weight loss and appear beneficial in a number of diseases (5). However, during these fasts, it is crucial to draw from a wide variety of food sources to maintain a diverse and healthy gut. The mission of RYH is exactly that: to improve gut health through a diverse diet, tailored to your needs, which you can start today!
Table 1. Three different types of fasting regimens and what each entails (5).
| Fasting regimen | What it involves |
| Alternate day | Fasting every other day |
| 5:2 diet | Fasting days interspersed with non-fasting days (5:2 refers to 5 non-fasting and 2 fasting days) |
| Time-restricted | Food intake within a specified timeframe and fasting for the rest of the time |
Is fasting good for your immune system and gut bacteria?
The gastrointestinal tract is full of bacteria, living in harmony with immune cells, until a detrimental bacterium is introduced or an external, environmental factor changes. The peaceful interactions between bacteria and immune cells are critical for a healthy gut, whereas perturbations in these interactions might result in disease. Various studies have focused on the effects of fasting on immune cells, bacterial diversity in the gastrointestinal tract and different diseases.
The effect of fasting has been investigated in human volunteers and mice, with one study highlighting that fasting reduces the numbers of an immune cell, called a monocyte, which can produce inflammatory signals (6). The authors ensured that the depleted monocyte numbers could still launch a fight against bacterial pathogens in mice. Therefore, fasting could diminish inflammation but preserve the combat abilities of monocytes. The potential benefit of intermittent fasting in various diseases has been interrogated primarily in animal models. For instance, in a mouse model of multiple sclerosis, a debilitating neurodegenerative disease, fasting ameliorated disease severity (7). Specifically, the authors found that this was mediated at least in part by the bacteria resident in the gastrointestinal tract. Additionally, a separate study on obesity in animal models revealed that alternate day fasting impacted the gut bacterial composition of mice (8). These changes resulted in different fermentation products being produced by the bacteria and an improvement in their obesity scores. While these studies have been performed on animal models, there may be benefits worth exploring in humans in several diseases. However, further research is required into long-term effects of fasting to draw a conclusion about its merits.
So, is fasting good for you?
In conclusion, there are multiple studies highlighting the positive effects of fasting, but these are based on a short timeframe. Further controlled studies over a longer period of time will give us a better understanding on the positive and potentially negative effects of fasting. Before embarking on a strict fasting routine, make sure you double check that this would be a healthy option for you with your GP.
References
1. de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019;381(26):2541-51. https://www.nejm.org/doi/full/10.1056/NEJMra1905136
2. Longo VD, Mattson MP. Fasting: molecular mechanisms and clinical applications. Cell Metab. 2014;19(2):181-92. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3946160/
3. Yang H, Shan W, Zhu F, Wu J, Wang Q. Ketone Bodies in Neurological Diseases: Focus on Neuroprotection and Underlying Mechanisms. Front Neurol. 2019;10:585. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6581710/
4. Puchalska P, Crawford PA. Multi-dimensional Roles of Ketone Bodies in Fuel Metabolism, Signaling, and Therapeutics. Cell Metab. 2017;25(2):262-84. https://www.sciencedirect.com/science/article/pii/S1550413116306556
5. Patterson RE, Sears DD. Metabolic Effects of Intermittent Fasting. Annu Rev Nutr. 2017;37:371-93. https://www.annualreviews.org/doi/abs/10.1146/annurev-nutr-071816-064634
6. Jordan S, Tung N, Casanova-Acebes M, Chang C, Cantoni C, Zhang D, et al. Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool. Cell. 2019;178(5):1102-14 e17. https://www.sciencedirect.com/science/article/abs/pii/S0092867419308505
7. Cignarella F, Cantoni C, Ghezzi L, Salter A, Dorsett Y, Chen L, et al. Intermittent Fasting Confers Protection in CNS Autoimmunity by Altering the Gut Microbiota. Cell Metab. 2018;27(6):1222-35 e6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6460288/
8. Li G, Xie C, Lu S, Nichols RG, Tian Y, Li L, et al. Intermittent Fasting Promotes White Adipose Browning and Decreases Obesity by Shaping the Gut Microbiota. Cell Metab. 2017;26(5):801. https://www.sciencedirect.com/science/article/pii/S1550413117305041