Water Fasting Safety: What You Need to Know Before You Fast

Drs. Joanna and Asa Frey, co-directors of the only Hispanic and bilingual clinical fasting center, located in a serene countryside oasis in the mountains of Puerto Rico.

Safety of Prolonged Water Fasting

Clinically supervised water fasting—periods in which only water is consumed, the patient remains at rest, and is under proper medical supervision—has gained attention for its potential metabolic and therapeutic effects.

However, water fasting is a powerful physiological intervention, not a wellness trend, and it carries real safety considerations that must be understood before attempting it.

Water Fasting Triggers Rapid Physiological Changes

During a water fast, the body undergoes significant metabolic changes, including alterations in:

• Blood glucose regulation

• Hormonal signaling

• Electrolyte balance

• Inflammatory and stress responses

  
  

These changes can occur within just a few days and affect multiple systems in the body at the same time.

Why Clinical Supervision Is Essential

A supervised water fast includes regular clinical monitoring to assess:

• Blood pressure and heart rate

• Blood glucose levels

• Electrolytes and hydration status

• Kidney and liver function

  
  

Without supervision, early warning signs can go unnoticed, increasing the risk of complications.

Is Water Fasting Safe for Most People?

Prolonged, supervised water fasting is a modality in which many people can safely participate. However, there are important exceptions. It is not appropriate for individuals who:

• Have a history of eating disorders such as bulimia or anorexia

• Are pregnant

• Have advanced kidney disease

• Are experiencing severe nutritional deficiencies

• Cannot safely discontinue or adjust certain medications

  
  

A free 5-minute consultation with Drs. Frey, professionals trained in therapeutic water fasting, can help determine whether fasting is appropriate or whether another therapeutic approach would be safer.

Refeeding After a Water Fast Is Critical

Safety does not end when the fast is over. Improper re-feeding after a water fast can trigger dangerous electrolyte imbalances and metabolic stress. For this reason, a structured, gradual, and professionally guided re-feeding process is a fundamental component of any safe fasting protocol. Many of the benefits of fasting continue for weeks after the fast ends. That is why supervised clinical fasting is so powerful:it is not an event — it is an advanced health intervention.

Why Preparation Before Fasting Is So Important

One of the most overlooked aspects of water fasting safety is what happens before the fast begins.

At our clinic, most patients do not fast immediately. Instead, they first enter a structured Health Program designed to prepare both the body and the individual for fasting.

Our Pre-Fasting Preparation Process

Before considering any fast, patients participate in a comprehensive program focused on restoring baseline stability and health. This process includes:

• Complete clinical evaluation and eligibility criteria

• Education on how fasting affects the body and what changes may occur

• Nutritional optimization recommendations

• Improvement of digestion, glucose regulation, and hydration status

• Lifestyle stabilization, including sleep, movement, and stress management

  
  

By improving health first, fasting — if and when it becomes appropriate — becomes:

• More comfortable

• More effective

• Lower risk

  
  

During this preparatory phase, patients experience clinically meaningful improvements across multiple domains of health, allowing them to begin fasting in a more stable physiological and psychological state. This prior optimization enhances tolerance to fasting and amplifies its restorative effects at the metabolic, neuroendocrine, and emotional levels.

Consistently, the vast majority of patients who complete the Health Program first report significant improvements in emotional well-being, greater cognitive clarity, and an increased sense of self-regulation and body awareness — key factors for adopting and sustaining healthy lifestyle changes long term.

Conclusion: Safety in Water Fasting

Water fasting can produce profound physiological effects, but those same effects create risks when undertaken without proper evaluation and supervision.

A safe water fast requires:

• Prior clinical evaluation

• Continuous clinical monitoring

• Structured refeeding and post-fast follow-up

If you are considering water fasting, education, preparation, and medical guidance must come before the fast — not after.

If you are interested in exploring supervised clinical fasting at Back to the Garden or learning whether you are a candidate, click here to learn more about the process, outcomes, and options.

Learn more about our fasting program here:https://www.backtothegardenpr.com/programa-de-ayuno-cl%C3%ADnico