What prolonged fasting can do to the human body | Explained - The Hindu
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Activist Sonam Wangchuk is on an indefinite hunger strike at New Delhi’s Jantar Mantar, seeking resignation of Union Education Minister Dharmendra Pradhan over alleged examination irregularities and NEET paper leak. | Photo Credit: Shashi Shekhar Kashyap
The story so far: As Sonam Wangchuk’s indefinite fast entered its 21st day on Saturday (July 18, 2026), concerns have emerged about his health. As the 59-year-old Mr. Wangchuk protests the continuation of Education Minister Dharmendra Pradhan in his position, in solidarity with the protests organised by the Cockroach Janata Party (CJP), and the central government is yet to engage with them, experts have flagged serious concerns about his health and the impact of prolonged fasting on the human body.
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Fasting is not new to humans. Multiple groups of people undertake fasts frequently, for religious, health or other cultural reasons. Those acclimatised to the process of fasting have developed the ability to stay without food for the specific period of the fast. In some Indian health systems, fasting is also counted as part of the therapy. However, concerns emerge as age and duration of the fast advances.
New findings from controlled studies across the world reveal that the body undergoes significant, systematic changes across multiple organs during prolonged periods of fasting.
Primarily, during fasting, the body changes its source and type of energy, switching from consumed calories to using its own fat stores. Prolonged fasting for 5-20 days produces weight loss — mild to moderate — of 2% to 10% and potent increases in circulating ketones, concludes a study published in the peer reviewed journal Nutrition Reviews.
A study published in Nature Metabolism, for instance, which recruited 12 healthy volunteers to take part in a seven-day fast, where they were allowed to drink water but could not consume any food, showed fluctuations in different blood proteins. This included an increase in coagulation factor XI, thus potentially heightening the risk of thrombosis events.
In a Chinese study published in Nature, during a 21-day complete fasting trial, there was a significant decrease in body weight, a reduction in blood glucose, an increase in blood ketones and blood uric acid, a continuous decline in resting energy expenditure, and the respiratory quotient tending towards fat metabolism, meaning the body is shifting its primary energy source away from carbohydrates and toward burning fats.
The adverse effects from the breaking down of muscle protein could range from headaches, insomnia, hunger, and sometimes metabolic acidosis (where the body accumulates too much acid). Of course, experts point out that a lot of the impact depends on how long the fast lasts, how well hydrated they are, and their health condition before they started the fast.
While mild imbalance can cause headaches, dizziness, cramps, fatigue, palpitations, constipation, continuing the deficit calorie situation leads to weakness, disorientation, numbness, or fainting.
Severe electrolyte imbalance during fasting can disrupt the electrical and chemical processes that keep the heart, brain, nerves, and muscles ticking. In extreme cases, it could cause cardiac rhythm disturbances, profound weakness, confusion, seizures, and, also fatal, if the fasting continues.
The most immediate long-term risk is loss of lean mass, not just fat. In prolonged catabolic (the process of breaking down complex food molecules to simpler units, in order to generate chemical energy) states, the body enters a negative nitrogen balance, which reflects ongoing protein breakdown and can lead to reduced strength, poorer mobility, and impaired physical function over a longer period.
Doctors also factor in an immune and infection risk, because protein-calorie malnutrition is linked to dysfunction of the immune system, which in a chain reaction, opens the door for infections and can prolong illness, ultimately once again impacting on catabolism.
Extended catabolic stress, they say, means the body stays in a breakdown state for too long, using muscle and other tissues to meet energy needs. Over time, this can cause muscle wasting, weakness, immune dysfunction, slower recovery, and higher overall illness risk. It can cause a multitude of other impacts – including affecting bone health and the capacity for rehabilitation, hormonal and metabolic strain, and the depletion of the body’s reserves.
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Refeeding should be initiated in a slow and structured process, because the body, after a prolonged fast, is vulnerable to fluid and electrolyte shifts when food returns. The main medical concern at this stage is refeeding syndrome, which can cause dangerous drops in phosphate, potassium, magnesium, and thiamine, leading to heart, nerve, and breathing problems. During fasting, insulin stays low and the body runs on fat and ketones.
When food is reintroduced, insulin rises, cells rapidly pull in glucose and electrolytes, and that shift can overwhelm a depleted system if feeding is too aggressive. Medically supported refeeding with a view to keeping the electrolytes on balance would be ideal.
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