Intermittent fasting is not without risks: Here's what happens to the body during 36 hours without food

Intermittent fasting has surged in popularity, often promoted on social media as a simple path to weight loss and improved health. However, extending fasting periods to 24, 36 hours, or longer, represents a more demanding form of restriction that can profoundly affect the entire body. An animated medical simulation illustrates how the body gradually adapts to a 36-hour fast, transitioning from glucose reliance to increased fat burning.

Despite these metabolic shifts, experts warn that such regimens are not risk-free. Professor James Betts, a metabolic physiologist at the University of Bath, highlights that many assumed health benefits of this metabolic state remain unconvincingly confirmed by human research. He notes that dramatic health advantages, sometimes promised on social media, are not clearly visible in the short term.

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numerous assumed health benefits of such a metabolic state have not yet been convincingly confirmed by research on humans

Extended fasting can quickly lead to unpleasant consequences. Common side effects include intense hunger, fatigue, low energy, headaches, dizziness, irritability, and mood swings. Other issues may arise, such as constipation, bloating, bad breath, sleep disturbances, frequent urination, and dehydration. Repeated or prolonged strict food restriction also increases the risk of insufficient nutrient intake, potentially leading to nutritional deficiencies and malnutrition in more extreme cases. The Emily Program, an organization focused on mental health and eating disorders, points out that high-quality long-term data on intermittent fasting is still limited, with many studies being short-term, involving small numbers of participants, or having high dropout rates, making it difficult to draw firm conclusions about long-term benefits and risks.

Furthermore, the relationship between fasting and eating disorders is sensitive. While intermittent fasting itself is not an eating disorder, the constant disregard for hunger and strict control over eating times can contribute to an unhealthy relationship with food for some individuals.

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the amount of quality long-term data on intermittent fasting is still limited