Once a niche practice, fasting is now part of the mainstream health conversation. One of the more extreme forms is water fasting, where only water is consumed for a set period. The practice has gained attention as a way to potentially reset the body, support metabolic health and improve overall wellbeing. Still, it comes with its risks and isn’t for everyone.
Health and wellbeing coach Janine McKenzie-Minifie works with clients in their 50s and 60s to build habits that prevent chronic disease and support a healthy, active retirement. She says that while water fasting can be powerful, it must be approached carefully.
When the body isn’t processing food, it shifts how it produces energy. On the first day, it burns stored sugar called glycogen. McKenzie-Minifie finds the first day hardest, as this is when hunger signals are strongest. “It’s a wonderful phase for using mindset processes to clean up stored emotions that are always there, but usually covered up with eating.”
The body undergoes a metabolic switch known as ketosis. Instead of relying on glucose from recent meals, it begins to draw on stored fat for fuel. This shift is the first phase of a water fast and normally occurs after around 12 hours. “This is when headaches, nausea, and body aches can occur.”
The second phase is autophagy, a natural cellular process where the body breaks down and recycles damaged components. It’s thought to kick in after 24 to 48 hours of water fasting. While much of the research on autophagy comes from animal studies, early human evidence suggests it may play a role in reducing inflammation and supporting metabolic health.
She compares autophagy to being snowed-in and needing to burn a fire to keep warm. “Once the firewood (the glucose) is burned through, you’d throw unwanted items like the broken chair and other junk onto the fire. The body sacrifices its damaged cells and weak muscle fibres to supply you with energy.”
However, McKenzie-Minifie is clear that not everyone has the metabolic flexibility to shift into this phase. “It can be dangerous for some people to water fast, so make sure you talk with your doctor first.”
Experiences during a water fast vary widely. In the early stages, people often report hunger, fatigue, irritability and headaches as the body adjusts. Some say these symptoms ease after a few days, replaced by more stable energy and mental clarity, though this is not universal. For others, symptoms persist or worsen, so they stop.
With years of experience and careful preparation under her belt, McKenzie-Minifie sometimes undertakes extended water fasts lasting over a week, using prior dietary adjustments to ease the transition. She says these longer fasts are only safe when built up to and approached gradually and undertaken with careful planning and close monitoring.
In her personal experience, she sometimes undertakes extended water fasts lasting over a week. By preparing with a low-calorie, plant-based diet to enter ketosis first, she reduces early fasting symptoms and describes the deeper phase, around day five onward, as feeling lighter, more energetic, and mentally clear, a state she calls a ‘faster’s high’.
Perhaps what happens before and after a water fast is more important than the fast itself. McKenzie-Minifie says water fasting can be dangerous without preparing properly or if the fast is broken without following safe refeed steps.
She recommends easing into a fast with a simplified, plant-based diet, reducing processed foods and lowering overall calorie intake. This approach can help the body transition more smoothly into ketosis, potentially reducing symptoms like dizziness, headaches and fatigue that often accompany the early stages of fasting.
Breaking a fast also requires care. After an extended period without food, the body becomes more sensitive to sudden increases in calories, especially carbohydrates, and metabolism slows. A large amount of food after a fast can overwhelm the body. “After a longer fast, the danger is refeeding syndrome, which can be fatal.”
While interest in water fasting continues to grow, the evidence remains mixed. Some studies suggest fasting can improve insulin sensitivity, support weight loss and reduce inflammation. Others highlight risks such as nutrient deficiencies, dehydration, muscle loss and hormonal disruption.
It is generally not recommended for pregnant or breastfeeding women, people with eating disorders, or those with certain medical conditions unless under medical supervision.
The liver and kidneys already work continuously to remove waste and toxins, regardless of diet. While fasting may influence metabolic processes, it does not replace the body’s built-in detoxification systems.
For those interested in water fasting, McKenzie-Minifie suggests a gradual introduction. She also advises everyone to consult with health professionals before participating in any physical or dietary changes.
“I like people to start slowly, by intermittent fasting by reducing the eating window, introducing a healthier diet and lifestyle, and eating foods that support the organs of detoxification before trying your first one-day fast.”
Water fasting isn’t a one-size-fits-all solution. Individual responses to fasting can differ significantly. Those considering it should focus first on sustainable life changes such as balanced nutrition, regular movement, quality sleep and stress management. Fasting is best viewed as one tool among many, as opposed to a cure-all.
Water fasting can disrupt electrolyte balance, particularly sodium and potassium levels, increasing the risk of serious complications such as heart rhythm disturbances. Prolonged fasting can also lead to significant muscle loss, including the breakdown of essential lean tissue, even in otherwise healthy people.
As interest continues to grow, experts agree on one thing: if water fasting is to be explored, it should be done with care, credible guidance and a clear understanding of both its potential benefits and its risks.
Janine McKenzie-Minifie has worked in the health and wellbeing sector for more than two decades, with a background spanning pharmacy, neuromuscular therapy and high-performance sport.
