Fasting is often seen as a powerful tool for improving health, but the effects it has on the body remain underappreciated. Understanding what happens inside the body during a fast can shed light on why it has garnered attention for its potential benefits. Dr. Maneendra, consultant and head of the critical care department at Gleneagles Hospitals in Hyderabad, shared insights on how the body responds when it goes without food for up to 24 hours.
In the first four hours after eating, the body’s focus is on digesting food and absorbing nutrients. This is the period when blood sugar and insulin levels rise. These spikes are essential as they provide energy to the body’s cells. During this time, the body relies on carbohydrates, especially glucose, which is broken down from the food consumed. Dr. Maneendra explained that the surge in blood sugar fuels daily activities, keeping the body energized and functioning smoothly.
As the hours progress, between four and eight hours after eating, digestion finishes and the body begins a shift in its energy sources. Blood sugar and insulin levels drop back to normal as the body starts using stored glucose, or glycogen, in the liver and muscles. Glycogen is the body’s way of keeping extra energy in reserve, and this process allows for sustained energy without the need for additional food intake. At this stage, people generally don’t feel hungry yet, as their bodies are still accessing their glycogen stores.
After eight to twelve hours without food, glycogen stores begin to run low. At this point, the body begins to transition into a state known as ketosis, where it turns to fat as its primary source of energy. During ketosis, fatty acids are broken down and converted into ketones, which are used to fuel the brain and muscles. This is often referred to as a fat-burning state and is one of the reasons why intermittent fasting has gained popularity among those looking to lose weight. According to Dr. Maneendra, the body’s ability to switch from burning glucose to burning fat for energy helps prevent muscle breakdown, preserving lean tissue while relying on fat stores.
The benefits of fasting are not just limited to weight loss or energy shifts. Dr. Maneendra pointed out that prolonged fasting, especially beyond the twelve-hour mark, may lead to more profound physiological changes. As the body continues to rely on fat stores, it triggers autophagy, a process in which the body breaks down and removes damaged cells, making room for newer, healthier cells. Autophagy has been associated with a host of health benefits, from improved immune function to a reduced risk of certain diseases, including cancer and neurodegenerative conditions.
As the fast extends beyond twelve hours and approaches the twenty-four-hour mark, the body remains in ketosis. Some individuals may experience heightened mental clarity and focus, which Dr. Maneendra attributes to the brain’s efficient use of ketones as a fuel source. Additionally, insulin levels continue to stay low, which can be beneficial for individuals with insulin resistance or those looking to improve metabolic health. The prolonged absence of food also lowers inflammation in the body, which is often linked to chronic diseases such as heart disease, diabetes, and arthritis.
It’s important to note, however, that while fasting has its benefits, it may not be suitable for everyone. Dr. Maneendra emphasized the importance of listening to the body and consulting with a healthcare professional before starting any fasting regimen. Fasting can place stress on the body, particularly in individuals with underlying health conditions or those who are pregnant, breastfeeding, or have a history of disordered eating.
For those able to safely fast, understanding the body’s natural response to fasting can provide a greater appreciation for the physiological benefits it offers. Whether for improved metabolic health, weight management, or general well-being, fasting may offer a promising approach. Yet, as with any dietary practice, moderation and individual consideration remain key.
As fasting extends beyond the 24-hour mark, the effects become even more pronounced. The body, still in a state of ketosis, becomes highly efficient at burning fat for fuel. This extended fasting period may enhance insulin sensitivity, which could be particularly beneficial for individuals at risk of type 2 diabetes. Dr. Maneendra highlighted that reduced insulin levels during prolonged fasting help the body respond better to insulin when food is eventually consumed, potentially lowering blood sugar levels more effectively.
Furthermore, the process of autophagy intensifies as fasting continues. The body becomes more adept at breaking down damaged cells and regenerating newer, healthier cells. This process is believed to have anti-aging effects as it rejuvenates the body from within, clearing away cellular debris and promoting overall longevity. The link between fasting, autophagy, and reduced inflammation is increasingly being studied, with promising results that suggest fasting could play a role in preventing or mitigating age-related diseases like Alzheimer’s and Parkinson’s.
As fasting continues, human growth hormone (HGH) levels may also rise, particularly after 24 hours of fasting. This hormone plays a critical role in tissue repair, muscle growth, and overall metabolism. Higher levels of HGH, combined with the body’s reliance on fat stores for energy, help preserve lean muscle mass during fasting. This is why many athletes or fitness enthusiasts incorporate fasting into their routines for both fat loss and muscle maintenance.
Despite these benefits, Dr. Maneendra reiterated that fasting beyond 24 hours should be approached cautiously. Prolonged fasting can lead to side effects such as dizziness, fatigue, irritability, and nutrient deficiencies if not managed correctly. For individuals considering extended fasts, proper hydration and electrolyte balance are crucial, as the body loses fluids and essential minerals while fasting. It’s also important to ease out of fasting by gradually reintroducing food to avoid overwhelming the digestive system.