What are the effects of fasting on the risk of Deep Vein Thrombosis (DVT) or other adverse clotting events?

Effects of Fasting on Risk of DVT and Adverse Clotting Events

Prolonged fasting may increase the risk of deep vein thrombosis (DVT) and other adverse clotting events due to dehydration-induced hypercoagulability, as demonstrated in recent case reports.

Mechanism of Risk

Fasting can potentially contribute to thrombotic risk through several mechanisms:

• Dehydration: Water-only fasting or prolonged fasting without adequate fluid intake can lead to significant dehydration, resulting in hemoconcentration and hypercoagulability 1
• Immobility: Prolonged fasting may be associated with reduced physical activity, especially during religious fasting periods or medically unsupervised fasting regimens
• Metabolic changes: Alterations in blood viscosity and coagulation factors during extended periods without food intake

Evidence on Fasting and Thrombosis Risk

The direct evidence linking intermittent fasting to DVT is limited but concerning:

• A 2023 case report documented a patient who developed lower limb DVT following a 2-week water-only fast that began with 5 days of complete food and water restriction 1
• The patient required 3 months of anticoagulation therapy with apixaban as recommended for provoked VTE events 1

Risk Assessment for Individuals Who Fast

When considering fasting regimens, the following risk factors for VTE should be evaluated:

• Age: Individuals over 60 years have increased risk 2
• Previous VTE history: Strongest predictor of recurrent events 2
• Immobility: Significant contributor to VTE risk (14.5% contribution to overall risk) 2
• Other factors: Active malignancy, acute infections, critical illness, and known thrombophilia 2

Recommendations for Safe Fasting Practices

To minimize thrombotic risk during fasting periods:

1. Maintain adequate hydration: Even during water-only fasts, ensure sufficient fluid intake
2. Incorporate regular movement: Avoid prolonged immobility; incorporate frequent ambulation and calf muscle exercises
3. Consider compression stockings: For individuals with additional risk factors, properly fitted below-knee compression stockings providing 15-30 mmHg pressure may help prevent DVT 2, 3
4. Medical supervision: High-risk individuals should consult healthcare providers before undertaking extended fasting regimens

Special Considerations for High-Risk Individuals

Individuals with the following conditions should exercise particular caution with fasting:

• Previous history of VTE
• Known thrombophilia
• Active malignancy
• Limited mobility
• Severe obesity
• Advanced age

Warning Signs During Fasting

Individuals practicing fasting should be vigilant for signs of DVT:

• Unilateral leg swelling
• Pain, redness, warmth, or tenderness in the leg
• Shortness of breath or chest pain (potential signs of pulmonary embolism)

Conclusion

While intermittent fasting may offer certain cardiovascular benefits 4, the potential risk of DVT due to dehydration-induced hypercoagulability should not be overlooked. The case report of DVT following prolonged water-only fasting 1 highlights the importance of maintaining adequate hydration and mobility during fasting periods. For individuals with pre-existing risk factors for VTE, medical consultation before undertaking extended fasting regimens is strongly advised.