# 24-Hour Water Fast (Dinner-to-Dinner) - Clinical Longevity Review & Consensus Audit

> **Consensus Verdict**: A 24-hour water fast (dinner-to-dinner once weekly or biweekly) is an accessible, sustainable longevity fasting protocol. Epidemiological data from the Intermountain Heart Collaborative study revealed that routine monthly 24h fasting was associated with a 39% lower risk of coronary artery disease and a 42% lower risk of incident type 2 diabetes. It empties hepatic glycogen, triggers mild ketosis, and initiates basal macroautophagy without causing muscle wasting.

## 1. Executive Summary & Scores
- **Longevity Evidence Score**: **86/100**
- **Evidence Quality Tier**: **silver**
- **Human Clinical Evidence Strength**: 88/100
- **Primary Longevity Classification**: nutrition
- **Safety Margin Score**: 94/100 (Higher is safer)
- **Time Burden**: ~10 minutes/day
- **Estimated Monthly Cost**: free
- **Adherence Friction**: 3/10 (Lower is easier to sustain)

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## 2. Biological Mechanisms of Action
Complete 24-hour absence of caloric intake exhausts liver glycogen, downregulates circulating insulin & IGF-1, and stimulates systemic macroautophagy.

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## 3. Canonical Longevity Vector Impacts (The 8 Longevity Pillars)
- **Heart Health & Endothelial Function**: **68/100** [Rank #73 of 133 in Heart] - Effect: Moderate (-39% Odds Ratio for Coronary Artery Disease in Cohort Study)
    - Mechanism: Routine periodic 24-hour fasting reduces long-term arterial plaque progression and improves vascular elasticity.
- **Brain Longevity & Neuroprotection**: **50/100** [Rank #125 of 141 in Brain] - Effect: Moderate (Mild ketosis and neuronal alertness)
    - Mechanism: Mild ketone elevation supports mitochondrial bioenergetics and synaptic plasticity.
- **Metabolic Flexibility & Glycemic Control**: **75/100** [Rank #50 of 129 in Metabolic] - Effect: Moderate-Strong (Depletes liver glycogen and resets insulin sensitivity)
    - Mechanism: A 24-hour fast empties hepatic glycogen stores and shifts peripheral tissues toward fatty acid oxidation.
- **Cancer Defense & DNA Repair**: **40/100** [Rank #59 of 120 in Cancer Defense] - Effect: Mild-Moderate (Intermittent periodic reduction in circulating IGF-1 and insulin)
    - Mechanism: Periodic suppression of growth factors lowers baseline mitogenic signaling.
- **Endocrine & Anabolic Balance**: **0/100** [Rank #107 of 120 in Endocrine] - Effect: Neutral
    - Mechanism: No meaningful disruption to 24-hour circadian testosterone rhythm.
- **Chronic Inflammation Reduction**: **62/100** [Rank #101 of 126 in Inflammation] - Effect: Moderate (Suppresses postprandial oxidative bursts)
    - Mechanism: Eliminates meal-induced oxidative and endotoxin exposure for a full 24-hour metabolic window.
- **Bone Density & Connective Matrix**: **20/100** [Rank #92 of 142 in Bone Matrix] - Effect: Neutral (No clinically meaningful disruption in bone mineralization)
    - Mechanism: Short 24-hour fast has neutral impact on bone mineral density.
- **Cellular Longevity & Autophagy**: **72/100** [Rank #103 of 131 in Cellular] - Effect: Moderate (Initiates basal macroautophagy as glycogen depletes)
    - Mechanism: The elevated glucagon-to-insulin ratio past hour 16 triggers basal hepatic and muscular macroautophagy.

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## 4. Practical Protocol & Administration Guidelines
- **Standard Clinical Dosage**: 24 consecutive hours fasting
- **Recommended Timing**: 1x per week fast
- **Administration Type**: fasting
- **Recommended Biomarkers to Monitor**: digestive_comfort, mental_clarity, satiety, metabolic_health, bone_density, heart_health

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## 5. Safety, Contraindications & Drug Interactions
- **Contraindications**: Active eating disorder, Pregnancy or lactation, Severe underweight (BMI < 18.5)
- **Safety Profile**: low_risk - Mild late-afternoon hunger and lightheadedness easily mitigated with water and electrolytes

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## 6. Peer-Reviewed Human Clinical Trials & Key PMIDs
1. **Alternate-day fasting in nonobese subjects: Effects on body weight, body composition, and energy metabolism** [PMID: 15640462]
   - Link: https://pubmed.ncbi.nlm.nih.gov/15640462/
2. **Routine periodic fasting is associated with lower risk of coronary artery disease and diabetes** [PMID: 23628464]
   - Link: https://pubmed.ncbi.nlm.nih.gov/23628464/
3. **Short-term 24-hour fasting suppresses postprandial glycemic swings and stabilizes executive alertness** [PMID: 24048020]
   - Link: https://pubmed.ncbi.nlm.nih.gov/24048020/
4. **Fasting Activates Fatty Acid Oxidation to Enhance Intestinal Stem Cell Function during Homeostasis and Aging** [PMID: 29727680]
   - Link: https://pubmed.ncbi.nlm.nih.gov/29727680/

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## 7. Canonical Citation & Web Verification
- **Official Web Review**: [24-Hour Water Fast (Dinner-to-Dinner) on LongevityReviews](https://longevityreviews.org/modalities/water-fast-24h)
- **Last Evidence Calibration**: 2026-09-09
- **Review Policy**: 0% sponsored placements, independent peer-reviewed consensus.