Fasting and only drinking water for three days is being rumored by many people as a way to detoxify the body, re-establish metabolism and lose weight quickly.
However, according to medical experts, what happens in the body after 72 hours without eating is much more complex and stressful than the commonly advertised benefits.
Dr. Sunil Rana, Deputy Director and Head of Internal Medicine at Asian Hospital, said that when a person only drinks water for three days, the body quickly runs out of reserve energy.
The amount of glycogen in the liver usually runs out within the first 24 hours, causing blood sugar to decrease. To compensate, the body increases the secretion of hormones such as glucagon, cortisol and growth hormones to mobilize energy from fat," Mr. Sunil Rana explained.
At this time, the liver will convert fatty acids into ketones to provide energy for the brain and muscles – a state called nutritional ketosis.
Although in healthy people, blood sugar can stabilize at a lower level, the body still bears great metabolic pressure.
“After 72 hours, ketosis is clearer, but this is still a stressful adaptive phase, especially dangerous for people with low nutritional reserves,” Dr. Rana warned.
Supporters of prolonged fasting often believe that this method helps detoxify, restore cells and improve metabolism.
However, scientific evidence in humans is limited. According to Dr. Rana, some studies show that short-term fasting can activate the autophagy, which is a mechanism for cell recycling, but most reliable data comes from animal studies or fasting-simulating diets, not fasting just drinking water for a long time in humans.
Metabolic improvements, if any, are usually only temporary and easily lost when eating and drinking returns to normal," said Sunil Rana.
Conversely, the risks of water fasting have been clearly recorded. Hypoglycemia, dizziness, dehydration, low blood pressure and electrolyte disorders are common side effects.
After three days of not eating, the loss of sodium, potassium, and magnesium can affect heart rate, neurotransmission, and muscle function.
Although the brain gradually adapts to ketones, many people still experience headaches, irritability and reduced concentration.
More worryingly, muscle decomposition begins early. When glucose is deficient, the body uses amino acids from muscles to maintain the production of necessary energy.
Although important organs such as the heart are relatively preserved, bone muscle loss after three days can leave significant clinical consequences.
Dr. Rana emphasized that fasting and only drinking water is unsafe for many groups of people. People with diabetes (especially those taking insulin), chronic kidney disease, heart disease, gout, eating disorders, people underweight, pregnant or breastfeeding women, the elderly and people taking blood pressure medication or anticoagulants are all at high risk.
According to experts, those who want to improve metabolic health or control weight should choose safer methods, such as intermittent fasting for 14-16 hours each day.
“Sustainable health comes from long-term lifestyle changes, not extreme measures,” Dr. Rana concluded.
(The article is for reference only, not for professional advice. Always consult a doctor or medical expert if you have questions).
