What is extended water fasting?

Extended water fasting involves abstaining from all food for 72+ hours while consuming only water and essential electrolytes. This triggers autophagy, ketosis, and metabolic reset. Medical supervision is required for fasts exceeding 72 hours.

Is extended fasting safe?

Extended fasting carries significant medical risks including electrolyte imbalance, cardiac arrhythmias, and refeeding syndrome. It should only be undertaken with medical supervision and proper electrolyte supplementation. Not suitable for individuals with certain medical conditions.

What is refeeding syndrome?

Refeeding syndrome is a potentially fatal shift in electrolytes and fluids that can occur when reintroducing food after prolonged fasting. It requires careful protocol including B-complex vitamins, phosphorus supplementation, and gradual food reintroduction.

Fasting Calculator UK | BMR TDEE Weight Loss Projections

Your Metabolic Profile

Enter your details to calculate your Basal Metabolic Rate (BMR) and projected fasting timeline using the Mifflin-St Jeor equation—the most accurate method validated by medical research.

Biological Sex

Age

18 80

Weight

40 kg 200 kg

Height

140 cm 220 cm

Activity Level

Fast Duration

Your Metabolic Profile

Basal Metabolic Rate (BMR)

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Calories burned at complete rest (organ function, breathing, circulation)

Total Daily Energy Expenditure (TDEE)

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Total calories burned with your activity level

Daily Caloric Deficit

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Complete caloric deficit during water-only fast

Realistic Weight Loss Projection

IMPORTANT UK REGULATORY NOTICE:

This calculator uses the scientifically validated Mifflin-St Jeor equation (reference: Mifflin MD, et al. Am J Clin Nutr. 1990;51(2):241-7) to project theoretical calorie deficits based on thermodynamics.

However, UK ASA regulations prohibit weight loss claims exceeding 2 lbs (0.9 kg) per week. While the science may project greater fat loss during extended fasting, we are legally required to state:

⚖️ MAXIMUM CLAIMED WEIGHT LOSS: 2 lbs (0.9 kg) per 7 days

The calculations shown are for educational purposes only and do NOT constitute guaranteed outcomes. Your government knows better than peer-reviewed science, apparently. Individual results vary significantly.

Understanding the Numbers

Water Weight (Days 1-3): Initial rapid loss is primarily glycogen-bound water (3-4g water per 1g glycogen) plus sodium/water excretion from lowered insulin. This is necessary metabolic "unburdening" but not sustainable fat loss.

Fat Loss (Days 4+): True adipose tissue metabolism. The body oxidizes approximately 0.3-0.5kg fat per day depending on TDEE. This is the sustainable component.

Muscle Preservation: Growth hormone increases 3-5x baseline during fasting, protecting lean mass. Protein catabolism is minimal when proper electrolyte supplementation is maintained.

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Get Daily SMS Motivation

Receive daily encouragement, science-backed tips, and crisis intervention during your fast. Especially critical on Day 3.

Yes, send me daily motivation via SMS during my fast Free service. Opt-out anytime by replying STOP.

Message Schedule: Day 1 (8am), Day 2 (8pm), Day 3 (2pm - Crisis support), Day 4-7 (Morning motivation + Refeeding prep)

Your Next Steps

Medical Clearance

Consult your physician. Extended fasting is not suitable for everyone. Review contraindications.

Protocol Preparation

Study the 7-Day Protocol including electrolyte requirements and timeline expectations.

Refeeding Plan

Critical: Review safe refeeding to prevent refeeding syndrome before you start.

Support System

Use sound therapy for urge surfing and meditation for discipline.

METABOLIC RESET

Metabolic Calculator

Your Metabolic Profile

Your Metabolic Profile

Realistic Weight Loss Projection

IMPORTANT UK REGULATORY NOTICE:

Understanding the Numbers

Get Daily SMS Motivation

Your Next Steps

Medical Clearance

Protocol Preparation

Refeeding Plan

Support System

Your Fasting Protocol