Dry Fasting for Health & Longevity - Quick Reference Sheet
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Dry Fasting for Health & Longevity

Created on 10/02/2026 – Quick Reference based on Evidence Review created using AI4L / Opus 5.5 – Audit

Dry fasting, going without food and all fluids for part of the day or, rarely, several days, is a religious practice also promoted for longevity. Daytime fasting brings modest, short-lived drops in weight, body fat and blood pressure, with headaches, tiredness, shorter sleep and, on certain diabetes medicines, dangerously low blood sugar. Nothing yet shows removing water adds benefit beyond water-permitted fasting; multi-day dry fasting remains high-risk and largely unexamined. (Full Review)

Protocol

Dawn-to-dusk intermittent dry fasting (Ramadan model)
12–18 h daily for 29–30 days
No food or fluid from dawn to sunset, with pre-dawn and post-sunset meals; the most studied form
Eating-window structure
2–3 L fluid overnight
Water and a light starter, then a full meal with protein, vegetables, fruit and moderate salt
Prolonged dry fasting
24–36 h fasts common
3–5-day fasts studied only as a supervised five-day protocol at a monastery hospital
Time to effect
Weight and waist
Weeks 2–3
Peak shortly after the fasting month; most revert within 2–5 weeks
Blood pressure
During the fasting month
Modest fall; durability after the fasting month is unknown
Well-being and mindfulness
Third week
Mindfulness still elevated three months later

Benefits

Contraindications
  • Pregnancy or breastfeeding
  • Type 1 diabetes, or type 2 diabetes on insulin or sulfonylureas (HbA1c above 9% or severe hypoglycemia within the past 3 months)
  • Chronic kidney disease stage 3b–5 (eGFR below 45), kidney transplant without specialist oversight, or two or more prior kidney stones
  • Heart failure NYHA class III–IV, or heart attack within the past 3 months
  • Prior cerebral venous thrombosis, known thrombophilia (inherited clotting tendency) or sickle cell disease
  • Gout with a flare in the past 12 months, or serum uric acid above 8 mg/dL
  • Age 75 or older, or frail older adults
  • Current or past eating disorder, or BMI below 18.5 kg/m²
  • Lithium therapy, or epilepsy with a seizure in the past 3 months
  • Dry fasts longer than 24 hours without medical supervision
    •
Key Interactions
  • Insulin and sulfonylureas (glimepiride, gliclazide, glyburide)
  • SGLT2 inhibitors (empagliflozin, dapagliflozin)
  • Diuretics (furosemide, hydrochlorothiazide, spironolactone)
  • ACE inhibitors and ARBs (lisinopril, ramipril, losartan)
  • NSAIDs, over-the-counter (ibuprofen, naproxen, high-dose aspirin)
  • Warfarin
  • Levothyroxine
  • Estrogen-containing oral contraceptives (ethinylestradiol combinations)
  • Multiple-daily-dose drugs (e.g., amoxicillin, levetiracetam)
  • Caffeine (coffee, energy drinks, caffeine supplements)
  • Glucose-lowering supplements (berberine, cinnamon extract, chromium)
  • Creatine and high-dose vitamin C (above 1 g daily)
  • Herbal diuretics (dandelion, horsetail, high-dose green tea extract)
  • Heat, sauna, alcohol and endurance exercise
    •

Risk & Side Effects

  • High: Hypoglycemia With Glucose-Lowering Medication
    •
  • Medium: Headache and Migraine Aggravation; Hypohydration Fatigue and Reduced Alertness; Shortened Sleep
    •
  • Low: Transient Kidney Strain; Kidney Stone Formation; Peptic Ulcer Complications; Hyperglycemia and Ketoacidosis in Diabetes; Uric Acid Elevation; Cerebral Venous Thrombosis in Predisposed People; Stress-Hormone and Lipid Surge in Multi-Day Fasts; Fat-Free Mass Loss; Reduced Exercise Performance; Accelerated Aging From Chronic Under-Hydration
    •
  • Speculative:

Monitoring

Marker Target Why
Serum sodium 137–142 mmol/L Hydration status
Creatinine & eGFR eGFR above 90 mL/min/1.73 m² Kidney strain
BUN 10–16 mg/dL Dehydration signal
Uric acid Below 5.5 mg/dL Gout and stone risk
Potassium 4.0–4.8 mmol/L Electrolyte balance
Fasting glucose 75–90 mg/dL Glucose control
HbA1c Below 5.4% Three-month glucose average
LDL-C, apoB, TG LDL-C below 100 mg/dL; apoB below 80 mg/dL; TG below 100 mg/dL Cardiovascular risk
hs-CRP Below 1.0 mg/L Inflammation
Hematocrit 40–50% (men); 37–45% (women) Blood thickening from dehydration
Urine specific gravity 1.005–1.020 on waking Overnight rehydration adequacy
Blood pressure Below 120/80 mmHg Cardiovascular effect and standing drop
TSH (levothyroxine users) 0.5–2.5 mIU/L Thyroid dose adequacy
Body weight, waist and body composition Improved weight and waist Success criterion

Cadence: Baseline panel before a first fasting month or any dry fast longer than 24 hours; weight and blood pressure weekly; laboratory tests in week three and two to four weeks after the fasting month, then annually; daily mid-day and pre-sunset glucose on glucose-lowering medication; daily weight, sodium and creatinine under clinical supervision in multi-day fasts

Qualitative Assessment

  • Energy and concentration in the last hours of the fast
  • Headache frequency and severity
  • Thirst intensity and urine color on waking
  • Dizziness on standing
  • Sleep duration and quality
  • Mood, irritability and sense of well-being
  • Exercise tolerance and recovery
Not medical advice. Educational distillation of a single evidence review. Confirm any decision with a qualified clinician, especially in the presence of prescription drugs or chronic conditions.