How the Body Adapts During a 25-Hour Fast
Translated & summarized from Now 14 by baba
During Yom Kippur's 25-hour fast, the body shifts from using food energy to internal fat and glycogen stores. Individual experiences of hunger, thirst, fatigue, and headaches vary based on personal health and habits.
The story in 5 lines · by baba
- The body gradually shifts energy sources during a 25-hour fast.
- Initial hours use food energy, then glycogen, then fat.
- Ketone bodies are produced for brain energy.
- Fasting symptoms like thirst and fatigue vary individually.
- The body adapts by utilizing internal reserves.
Yom Kippur, a significant Jewish holiday, involves a complete cessation of eating and drinking for approximately 25 hours. During this period, the human body undergoes a series of gradual metabolic shifts to maintain function.
In the initial hours after the pre-fast meal, the body primarily utilizes energy from consumed food, with blood sugar levels rising and the body using glucose. Simultaneously, it begins to tap into glycogen stores, mainly in the liver and muscles. As the fasting continues and no new food is ingested, the body progressively reduces its reliance on dietary glucose.
The body then transitions to using its internal reserves. Liver glycogen helps maintain blood sugar levels, and subsequently, fat becomes a more significant energy source. The liver also produces ketone bodies from fatty acids, which the brain can use as an alternative energy source during prolonged fasting. However, the body continues to produce glucose internally to supply tissues that require it.
Physical sensations experienced during the fast vary greatly among individuals, influenced by hydration habits, diet, and overall health. Fluid deficiency can lead to thirst, dry mouth, headaches, and dizziness. For regular coffee drinkers, caffeine withdrawal can also contribute to headaches. As the fast progresses, the lack of food and water becomes more pronounced, manifesting as fatigue, weakness, or difficulty concentrating for some, while others may primarily feel hunger and thirst.
Ultimately, a 25-hour fast represents a substantial deviation from normal routine, but the body is equipped to adapt by shifting from external food energy to internal stores. The subjective experiences during this time differ from person to person, highlighting the individual nature of physiological responses to fasting.
