Fasting and the Human Mind

Author:  Dyna Rochmyaningsih
Institution:  Bogor Agricultural University, Indonesia

As a spiritual practice, fasting has been employed by many religious groups since ancient times. Historically, ancient Egyptians, Greeks, Babylonians, and Mongolians believed that fasting was a healthy ritual that could detoxify the body and purify the mind. In the modern era, three major religions in the world also advise fasting at certain times:, such as Judiasm during Yom Kippur, Christianity during the Lent period, and Islam during the festival of Ramadhan. Their beliefs are that fasting is a way to communicate with the Divine Being through the purification of the body and mind. The other major religions, such as Budhism and Hinduism also highly recommend this practice. In addition, the Natives Americans of Mexico and the Incas of Peru also observed fasting as the form of penance to their gods. Thus, throughout history, fasting has always been observed as a form of mind purification with a spiritual or religious intention and the act connotes spirituality.

This relationship is an abstract idea constructed by our collective historical experiences. Some fasting observers report that they have a sharper and more focused mind when they fast. But what do they mean? Is fasting truly mind-purifying?

Scientific realm defines the mind as cognition. It comprises of mental processes involved in gaining knowledge and comprehension, including thinking, knowing, remembering, judging, and problem solving. These are higher-level functions and encompass language, imagination, perception, and planning (Wagner 2009). Those functions are processed in the brain. The brain consists of billions of nerve cells. Just like other types of cells in the body, nerve cells need enough energy to work. This energy only comes from glucose. Therefore, to perform tasks such as memorization, the human brain needs sufficient glucose to meet its high energy demand.

Fasting is a condition when there is a temporary lack of glucose intake to the body. Glucose itself is the main fuel for the brain. Therefore it is logical to assume that humans have worse memory performance when fasting than when they are not.

However, evidence suggests that the lack of glucose while fasting does not hamper glucose availability in the brain. Our body is has v very sophisticated system of energy processing and has mechanisms to balance our physiological system via a process called homeostasis. So, when the body detects a lack of glucose, it tries to make glucose from other sources inside the body, such as glycogen and proteins. This new formation of glucose (gluconeogenesis) can balance glucose availability in the brain for 24 hours. This mechanism is also hard at work during day fasting, such as during Ramadhan.

In Indonesia, it is a common thing to hear that most Muslims attribute their lack of concentration at work to fasting. Workers are sanctioned fewer hours of work during Ramadhan for the same reason. Hunger is a sensation which indicates an empty stomach. It does not represent a lack of energy in the body. Hunger is a sensation that is processed in the brain and can be a distracting feeling. However, it is important to note that the sensation of hunger will only persist for short periods of time and will usually go away if we focus on other things.

Another interesting discourse about fasting is its spiritual phenomenon. Some religious people in the world state that they have visions while they are fasting and meditating. For example, some have had sensation of meeting God or achieving Nirvana. However, unlike Ramadhan, to achieve these states of being, severe fasting is often observed for a long period of time. Some people will not have meals for days or even weeks. Physiologically, this condition alters the body's system of providing to the brain. While for short periods of fasting, the body can maintain energy availability by producing glucose from glycogen and proteins, during severe fasting, energy demands of the brain are fulfilled by ketone bodies. Ketone bodies yield energy in the form of ATP, which is used by nerve cells to maintain the membrane potentials needed to conduct electrical nerve impulses.

In comparison with glucose, ketone bodies are very good energy stores (Salway, 2004). One hundred grams of ketone bodies (hydroxybutyrate) can yield 10.5 kg ATP, which is a few times higher than the 8.7 kg of ATPs that can be produced from one hundred grams of glucose. Thus, it is reasonable to infer that the use of ketone bodies as the main fuel may produce different metabolic effects in the brain from the use of glucose.

For example, the different metabolism used in severe fasting may produce different mental processes, particularly in image perception. As implied in Hebb's postulate, the molecular workings of nerve cells are the basis of mental processing. Nerve cells work to record and retrieve memory, manipulate information, think, imagine, and perceive the world. In addition, these cells function and perform these tasks through electrical impulses. Therefore, changes in electrical impulses which are produced by ketone bodies may produce different image perception compared with normal electrical impulses produced by glucose. This image could be something that the fasting observant has never experienced before.

This phenomenon can also be seen in some non-fasting situations, such as fatigue, epileptic seizure, or near-death situations, when patients claim to "see" images without any visual input. For example, some runners report that they scan "see" abnormal images after 30 to 40 minutes of running and many people often see "heaven" when they are near death (Mikami, 1997). The same phenomenon may happen in people who meditate while fasting for long periods of time. Most of them reportedly see divine images and may feel that their mind has been purified as a result of the experience.

However, despite these eyewitness accounts, there is still a lack of scientific evidence in the field of fasting. There are still many other areas other than physiological mechanisms, such as ketone metabolism and the sensation of hunger sensation, that need to be examined to determine the extent to which ideas such as mind purification and fasting can be linked. Currently, there are many cognitive areas of our mind that are still not completely understood to explain the many acts on spirituality that are happening in this world. Indeed, perhaps more attention needs to be paid to the intersection between human nature and science to a more concrete explanation to be found linking fasting and spirituality.


Mikami A. 1997. Possible neurophysiological basis of visual images seen in Shamanism.

Salway JG. 2004. Metabolism at a glance. Oxford : Blackwell Publishing.

Wagner KV. 2009. What is cognition.

Written by: Guest contributor Dyna Rochmyaningsihh

Edited and published by: Hoi See Tsao