More Information


Intersections in Science was founded by the outreach team of UCLA’s science libraries. The group brings students and librarians together to publish research connecting science to the humanistic realities of our world. The team’s annual Science as Art competition encourages members of the campus community to share the beauty of science through artistic submissions.

As the holy month of Ramadan comes to an end, we wanted to explore the science behind fasting, its historical origin and the research that shows its health effects. Fasting has been around for many centuries and is well documented in several major world religions. Fasting looks different for each religion but many share similar characteristics: to repent, to reflect on a person’s spiritual journey and to heighten their spirituality. It can also serve as a way to experience sacrifice as a collective and generate solidarity within communities. While religious fasting focuses on spiritual journeys and community solidarity, a number of health effects have been uncovered through modern scientific research on fasting. We will be discussing some of the science behind fasting, religious practices that involve fasting, and modern diets such as caloric restriction or intermittent fasting.

The Science Behind Fasting

A report from the CDC states that approximately 42% of Americans were obese, and that obesity was associated with several chronic or preventable diseases such as heart disease, stroke, type-2 diabetes and certain types of cancer (CDC 2020). Over the past few decades, scientists have sought to understand the health effects of religious fasting and to identify if some forms of fasting can serve as a potential non-pharmacological intervention for improving health and increasing longevity (Trepanowski and Bloomer, 2010). Trepanowksi and Bloomer describe the three most common forms of fasting which are “caloric restriction (CR), alternate-day fasting (ADF) and dietary restriction (DR)” (Trepanowski and Bloomer, 2010:1). Caloric restriction is a decrease in calories between 20% and 40%. Alternate-day fasting is alternating fasting every 24-hours. Lastly, dietary restriction is the exclusion of specific foods from the diet like meat or dairy. In studies of these common fasts, some health benefits were observed such as a decrease in the incidence of cardiovascular disease, some cancers and even an increase in lifespan in animals.

In a literature review written by Trepanowski and Bloomer in the Cardiorespiratory/Metabolic Laboratory of the University of Memphis, the authors break down the benefits of Ramadan, Greek Orthodox fasting and the Daniel Fast. In this review, Trepanowski and Bloomer were able to conclude that the overall benefits of religious fasting are a decrease in body mass, total cholesterol and LDL-C/HDL-C ratio, key factors that indicate the risk for cardiovascular disease. The authors also identified confounding variables that could explain some of the variability between studies focused on health effects of fasting for Ramadan. These included differences in smoking rates, medication consumption a variability in overall diet, which can interfere with the efficacy of fasting and the beneficial effects that usually accompany fasting. In all, studies of religious fasting have been correlated with a decrease in chronic illnesses and improved lifespan.

Another review conducted by Persynaki et al. has arrived at similar conclusions relating to the benefits to religious fasting. In this review, Persynaki et al. compared results from non-religious fasting, religious fasting and fasting on animals. They have found that religious fasting has “beneficial effects on body weight and glycemia, cardiometabolic risk markers and oxidative stress parameters” (Persynaki et al., 2016:14). Persynaki et al. have found these benefits extend even to animals that experience fasting, showing benefits like weight loss and less insulin resistance. Some researchers, focusing on model organisms such as the nematode C. elegans and fruit fly D. melanogaster, have gone so far as to claim that “Calorie restriction is the most reasonable anti-ageing intervention” (Liang et al. 2018). Collectively, the scientific community seems to acknowledge that there are at least some health benefits of fasting from worms and flies all the way to humans.

Fasting in Religious Practice

A number of popular religions engage in some form of fasting. Many Christians practice Lent, in which they eliminate something from their daily life or diet such as TV or sugar. Other things that are eliminated are fish and meat on Fridays (Ali, 2020). There are several fasts that Jewish people take part in throughout the year. Yom Kippur, a particularly significant fast in the Jewish calendar, requires a 25-hour fast for men, women and children above 13 years old who are not medically exempt. On this day, Jewish people abstain from food and beverages while praying for forgiveness. Once the 25 hours have ended, the community gathers to have a feast together (Ali, 2020). Then there’s Ramadan, a one-month journey in which Muslims around the world refrain from eating and drinking between sunrise and sunset. It begins with Sahur, a morning prayer and a small breakfast before sunrise and ends with Iftar, an evening feast. The timing of Ramadan changes every year given that it is based on the lunar calendar but the timing of Ramadan is marked by a crescent moon (Ali, 2020). Buddhism requires a vegetarian-like diet that removes all animal products from the diet except milk or soybeans (Persynaki et al., 2016). The Buddhism fast typically occurs throughout the year in comparison to Lent, Ramdan, Yom Kippur and the Daniel Fast. Lastly, the Daniel Fast is based on the Bible’s Book of Daniel. It’s a 21-day fast where the only thing consumed is water, fruits and vegetables – almost like a vegan diet (Persynaki et al., 2016). All of these periods of fasting are concluded with some form of celebration, acknowledging the importance of community, spirituality and celebrating the completion of a period of sacrifice (Ali, 2020). Greek Orthodox fasting covers the holidays of Nativity, Lent and Assumption, covering about 180-200 days a year (Trepanowski and Bloomer, 2010). During these fasts, meat, dairy products, olive oil and alcohol are restricted primarily on Wednesdays and Fridays. Additionally, there is an increase in vegetables, bread, fruits, legumes and nuts as their primary diet. (Trepanowski and Bloomer, 2010).

Religious fasting falls under three types of fasting: caloric restriction, alternate-day fasting and dietary restriction. Each of these practices are incorporated in some form into religious fasting. Lent, Greek Orthodox fasting, the Daniel Fast and the Buddhism fast are focused more on diet restriction whereas Ramadan and Yom Kippur are more like caloric restriction. Religious scholars are aware of the health benefits of fasting – yet most religious texts and practices focus on the spiritual benefits. Interestingly, religious fasts hold some similarities to intermittent fasting, which is more popular than ever. Like religious fasts, intermittent fasting has helped some people with weight loss and establishing a healthy eating routine.

Modern Applications and Popular Diets

Through scientific studies, fasting has been shown to have physical benefits in addition to the spiritual benefits highlighted in religious traditions that involve fasting. These benefits are most readily apparent in populations suffering from weight- and diet-based morbidities. The studies highlighted above have indicated benefits including a decrease in body mass, cholesterol and risk of cardiovascular disease that have been backed by scientific experimentation. So what does fasting look like today?

A popular form of fasting is intermittent fasting, defined as “an eating pattern that cycles between eating and fasting” (Gunnars, 2020). There are many ways to practice intermittent fasting such as fasting for 16 hours and eating for 8 hours, fasting for 24 hours, and then eating for the next 24 hours, or even fasting every couple of days. The different ways of practicing intermittent fasting fall under the three types of fasting mentioned by Trepanowski and Bloomer, which are caloric restriction, dietary restriction and alternate-day fasting. Intermittent fasting looks quite similar to religious fasting in regards to the three common fasts they fall under mentioned earlier. The benefits still remain the same and even include insulin resistance and a boost in your metabolism. MedlinePlus has a page dedicated to answering five questions regarding the basics and potential research on intermittent fasting that can help you kick start intermittent fasting. There’s a scientific connection between religious fasting and intermittent fasting and all-in-all, both serve as means of bettering yourself, spiritually and healthily.


Fasting has been done for millennia and has been a way for people to connect with their spirituality and community. Recently, science has supported the benefits of all religious fasting that can increase lifespan and decrease risks for cancer and cardiovascular disease. Intermittent fasting has become a popular and go-to health tool to boost metabolism and create a healthy lifestyle. This form of fasting is similar to religious fasting minus the explicit spiritual effects, although that can be a boost for some. Religions such as Islam, Christianity, Buddhism and Judaism continue their traditions of fasting around the world, perhaps feeling some satisfaction that scientists now see they were also recalibrating their body’s health all along.

More information:


Ali, R. Lent, Ramadan, Yom Kippur: What do all these religious fasts mean? USA Today (2019).

Carroll, M.D., Fryar, C.D., Hales, C.M., Ogden, C.L., Prevalence of Obesity and Severe Obesity Among Adults: United States, 2017-2019. NCHS Data Brief No. 360. CDC (2019).

Gunnars, K. Intermittent Fasting 101 – The Ultimate Beginner’s Guide. Healthline (2020).

Liang, Y., Liu, C., Lu, M. et al. Calorie restriction is the most reasonable anti-ageing intervention: a meta-analysis of survival curves. Sci Rep 8, 5779 (2018). in a new tab)

Persynaki, A., Karras, Sp., Pichard, C. Unraveling the metabolic health benefits of fasting related to religious beliefs: A narrative review. Nutri J, 35 (2016). in a new tab)

Trepanowski, J.F., Bloomer, R.J. The impact of religious fasting on human health. Nutr J 9, 57 (2010). in a new tab)