Many people begin weight loss by " fasting " rather than " diet control " because they believe it's the fastest shortcut. However, this shortcut can lead to greater harm to the body than expected. Each day, our body gets energy from the food we eat. Prolonged fasting means no energy intake, which can impact the digestive system. Initially, when energy from nutrients is lacking, the body compensates by using energy from other sources. Normally, the body uses glucose as fuel to provide energy so muscles can move, the brain can think, and the heart can pump.
Normally, when we eat, excess energy is stored as "glycogen," mainly in the liver and muscles, to be used when blood sugar drops or during nutrient deficiency. The liver converts glycogen back to glucose for energy.
Once glycogen stores are depleted, the body breaks down fat, producing "ketones," molecules similar to sugar. If fasting continues and all reserves are used up, the body then begins breaking down muscle protein for energy.
Prolonged fasting not only causes nutrient deficiency but also impacts mental health. Hormonal changes can lead to depression, reduced hunger, and diminished desire to eat.
A person can survive without nutrients for about 6-8 weeks. However, this depends on hydration status because without water, survival is only 1-2 weeks. Dehydration impairs urination, causes waste buildup, which can lead to kidney failure, low blood pressure, or even shock and death.
When resuming eating, choose easily absorbable foods like gels that can help adjust the intestines and be absorbed immediately. Continue this for 4-7 days to allow the body to adapt by creating new cells and restoring digestion and absorption functions. Food types and amounts should be limited and gradually increased step by step, avoiding overly strong flavors. Monitor for diarrhea, which indicates the body is not ready to digest and absorb food.
Also, after prolonged fasting, beware of "Refeeding Syndrome," which happens when the body suddenly receives nutrients after deprivation. Cells simultaneously repair and consume energy, which can overwhelm the body’s adaptation and cause numbness, cramps, seizures, or spasms. Vitamin B1 is needed during this process to prevent complications.
If fasting continues or is too severe, the body adapts by lowering metabolism to save energy, resulting in " the harder it becomes to lose weight the more you fast." This can cause intense hunger, leading to uncontrolled overeating. Risks include nutrient deficiency, fatigue, dizziness, insomnia, mood swings, constipation, and long-term muscle and hormonal damage. If food restriction is necessary for weight control, it should be done safely by not cutting calories too drastically, choosing adequate protein and fiber, staying hydrated, eating balanced meals, and incorporating muscle-strengthening exercise to preserve muscle mass. Most importantly, aim for gradual, sustainable weight loss rather than extreme fasting, which may reduce scale numbers quickly but not improve shape or health.
Information provided by the Center of Excellence for Endoscopy, Gastrointestinal and Liver Diseases, Phyathai 2 Hospital.