Is water intake really restricted during fasting, particularly for individuals with underlying medical conditions such as kidney disease, heart failure, or those taking diuretics?

Water Intake During Fasting: Context-Dependent Restrictions

Water intake during fasting is NOT universally restricted—it depends entirely on the type of fasting being practiced. For religious fasting (particularly Ramadan), water is completely restricted during daylight hours, while for intermittent/therapeutic fasting, water is typically encouraged and unrestricted. 1, 2

Key Distinction Between Fasting Types

The critical difference lies in the fasting methodology:

• Religious fasting (Ramadan): Complete abstention from all food AND fluids from dawn to sunset 1
• Intermittent/therapeutic fasting: Voluntary abstinence from food while maintaining fluid intake 1, 3, 2

This distinction is fundamental because the health risks and management strategies differ dramatically between these approaches. 1

Dehydration Risks During Water-Restricted Fasting

High-Risk Populations

Patients with certain medical conditions face substantial risks when water intake is restricted during fasting and should generally avoid it. 1

The following groups are at very high risk for complications:

• Patients on chronic dialysis - cannot compensate for fluid restriction 1
• Advanced heart failure patients - risk of volume depletion and hemodynamic instability 1
• Severe kidney disease - impaired fluid/electrolyte regulation 1
• Patients taking diuretics - compounded dehydration risk 1

Physiological Consequences

Limitation of fluid intake during prolonged fasting causes dehydration that may become severe, especially in hot/humid climates or with physical labor. 1 Hyperglycemia can worsen this through osmotic diuresis, contributing to volume and electrolyte depletion. 1 Orthostatic hypotension may develop, particularly in patients with pre-existing autonomic neuropathy, potentially resulting in syncope, falls, injuries, and fractures. 1

Specific Disease-Based Recommendations

Liver Disease and Transplant Patients

Liver transplant recipients can fast only under meticulous medical supervision with guaranteed plenty of fluid intake (>3 L/day during non-fasting hours). 1 In a prospective study, 82.2% of liver transplant recipients who maintained high fluid intake (>3 L/day) successfully completed Ramadan fasting, though 11.1% had to stop due to rising renal function parameters. 1

Patients with decompensated liver disease, ascites, hepatic coma, or hematemesis should avoid fasting entirely regardless of their Child class, as it can seriously affect their health. 1

Diabetes Management

Patients with diabetes face a fivefold increase in severe hyperglycemia during Ramadan fasting (from 1 to 5 events per 100 people per month for type 2 diabetes). 1 The 2025 diabetes guidelines emphasize spacing fluid intake from Iftar to Suhoor to prevent dehydration, recommending at least 1.5-2 L of water during non-fasting hours. 1

For post-bariatric surgery patients with diabetes, dehydration has been shown to be responsible for urinary stone formation, making adequate hydration during non-fasting hours critical. 1

Cardiovascular Disease

Patients with stable cardiovascular conditions (stable angina, non-severe heart failure) may fast if their medications and clinical conditions allow, but must be educated on dehydration risks. 4 However, those with advanced heart failure, poorly controlled arrhythmias, or recent myocardial infarction should not fast. 4

Heart failure patients require careful fluid management—while the 2022 ACC/AHA/HFSA guidelines note that fluid restriction benefit is uncertain in advanced heart failure with hyponatremia, overly aggressive restriction may reduce quality of life. 1, 5

Diabetes Insipidus: Critical Exception

Patients with diabetes insipidus should NEVER have water restricted—this is a life-threatening error. 6, 7 These patients must have free access to plain water or hypotonic fluids 24/7 to prevent severe hypernatremic dehydration. 6, 7 Their fluid intake should be determined by thirst sensation rather than prescribed amounts, as their osmosensors are typically more sensitive than medical calculations. 6

If intravenous rehydration is needed, 5% dextrose in water (D5W) should be used, NOT normal saline or electrolyte solutions, as normal saline delivers a high sodium load to kidneys that cannot concentrate urine. 7

Therapeutic/Intermittent Fasting Protocols

Water Intake Encouraged

For medically supervised water-only fasting or intermittent fasting protocols, water intake is not only permitted but actively encouraged. 3, 8 A comprehensive safety review of 768 medically supervised water-only fasting visits found that the protocol was safe when water was consumed freely, with only 0.002% experiencing serious adverse events. 3

Time-restricted eating and alternate-day fasting protocols specifically allow and encourage fluid intake during fasting periods. 1, 2, 8

Critical Monitoring Requirements

For Religious Fasting with Water Restriction

Patients choosing to fast with water restriction require:

• Pre-fasting assessment of surgical history, complications, and diabetes status 1
• Electrolyte monitoring every 2-3 months for high-risk patients 6
• Education on terminating the fast if becoming unwell 4
• Post-Ramadan review to reassess risk status 4

For Therapeutic Fasting

Patients undergoing therapeutic fasting with water intake should have:

• Serum electrolytes checked within 7 days and at 1 month after starting treatment 6
• Close observation of clinical status, neurological condition, fluid balance, and body weight 7
• Guidance from certified fasting therapists to ensure adherence to safety standards 9

Common Pitfalls to Avoid

1. Never restrict water in diabetes insipidus patients—this leads to life-threatening hypernatremic dehydration 6, 7

2. Do not use normal saline for IV rehydration in diabetes insipidus—use D5W instead to avoid sodium overload 7

3. Avoid recommending water-restricted fasting for patients on dialysis, with advanced heart failure, or decompensated liver disease—these patients cannot safely compensate 1

4. Do not assume all fasting restricts water—clarify the specific fasting protocol being followed 1, 2

5. For heart failure patients, avoid both excessive fluid restriction and excessive fluid intake—individualized monitoring of volume status is essential 1, 5