Nutritionist Explains Benefits and Risks of 24–72 Hour Water Fasts

Water fasting, the practice of consuming only water for 24 to 72 hours, has emerged as a trending health and wellness method. Nutritionist Nmami Agarwal explains that this extreme fasting approach triggers unique metabolic processes in the body, including fat-burning, cellular repair, and mental clarity. While popular for weight management and detoxification, water fasting carries both benefits and risks that are important to understand.

During the first 12 hours of a water fast, the body relies on stored glucose for energy. Between 12 and 24 hours, it enters ketosis, a fat-burning state where stored fat is converted into energy. After 24 hours, a process called autophagy begins, where the body cleans and recycles damaged cells, contributing to cellular rejuvenation and improved organ function.

One of the main advantages of water fasting is improved insulin sensitivity. By making hormones like insulin and leptin more effective, fasting helps regulate blood sugar levels, lowers hunger signals, and reduces the risk of obesity and type 2 diabetes. Additionally, the calorie deficit created during fasting forces the body to utilize fat stores, potentially leading to fat loss over time.

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Beyond weight and metabolic benefits, water fasting may lower the risk of chronic diseases. It can reduce high blood pressure, cholesterol levels, and systemic inflammation, which may help prevent heart disease, diabetes, and certain cancers. Fasting also gives the digestive system a break, allowing energy to shift toward cellular repair and regeneration, ultimately supporting overall health.

Many people report enhanced mental clarity, reduced brain fog, and a sense of calm or heightened willpower while fasting. However, the practice comes with notable risks, including dizziness, headaches, fatigue, muscle loss, dehydration, and nutritional deficiencies. Water fasting is not recommended for everyone, particularly pregnant or breastfeeding individuals, underweight persons, or those with certain medical conditions like type 1 diabetes or heart disease.

“Fasting is a metabolic tool, not a magic solution,” Agarwal emphasizes. Anyone considering water fasting should do so under medical supervision to maximize benefits while minimizing potential harms. With careful planning, even a short fast can offer profound physiological and psychological effects—but safety must always come first.

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