What is the expected weight loss for a 180-pound man after 16 days of fasting?

Complete Fasting for 16 Days: Expected Weight Loss

A 180-pound man who completely abstains from eating for 16 days would lose approximately 16-24 pounds, but this is an extremely dangerous practice that should never be undertaken outside of intensive medical supervision due to severe risks of cardiac arrhythmias, electrolyte disturbances, muscle wasting, and death.

Physiological Reality of Complete Fasting

Expected Weight Loss Calculation

• Initial rapid loss (Days 1-3): Approximately 3-5 pounds from glycogen depletion and associated water loss 1
• Ongoing fat and lean tissue loss (Days 4-16): Approximately 1-1.5 pounds per day, totaling 13-19 additional pounds 1
• Total expected loss: 16-24 pounds over 16 days, though individual variation exists based on metabolic rate and body composition 1

Composition of Weight Loss

• Complete fasting results in substantial loss of both fat mass AND lean body mass (muscle, organ tissue) 1
• The Minnesota Starvation Experiment demonstrated that prolonged severe caloric restriction causes significant muscle wasting and organ tissue breakdown 1
• Unlike controlled caloric restriction, complete fasting accelerates lean tissue loss, which is metabolically harmful and difficult to recover 1

Critical Medical Dangers

Life-Threatening Complications

• Cardiac risks: Severe electrolyte imbalances (particularly potassium, magnesium, phosphate) can cause fatal cardiac arrhythmias within days 2
• Refeeding syndrome: When eating resumes after prolonged fasting, rapid shifts in electrolytes can cause heart failure, respiratory failure, and death 2
• Muscle wasting: Loss of cardiac muscle mass can impair heart function permanently 1
• Metabolic collapse: Severe hypoglycemia, ketoacidosis, and organ dysfunction 2

Why This Differs from Medical Recommendations

• Very low-calorie diets (VLCDs) providing ≤800 kcal/day show initial weight loss of 16.1% at 4 months under medical supervision, but complete fasting (0 calories) is categorically different and far more dangerous 2
• VLCDs require "close monitoring by an experienced physician, nutritionist, or dietician" and are limited to 12-16 weeks maximum 2
• Complete fasting has no legitimate medical indication for weight loss and is contraindicated 2

Evidence-Based Safe Alternatives

Recommended Approach for a 180-Pound Man

• Target caloric intake: 1500-1800 kcal/day creates a safe deficit for men 2, 3
• Expected safe weight loss: Approximately 0.5 kg (1 pound) per week with a 500-750 kcal/day deficit 3
• Over 16 days (approximately 2.3 weeks): Expected loss of 2-3 pounds safely 3

Medically Supervised Intensive Options

If rapid weight loss is medically necessary:

• Very low-calorie diet (VLCD): 800 kcal/day under strict medical supervision can achieve faster results 2
• Requires: Meal replacements, medical monitoring, electrolyte supplementation, and regular physician visits 2
• Maximum duration: 12-16 weeks, not appropriate for unsupervised use 2

Long-Term Consequences of Extreme Fasting

Metabolic Adaptation

• The Minnesota Starvation Experiment revealed that severe food deprivation triggers profound metabolic adaptations that persist long after refeeding 1
• These adaptations include reduced basal metabolic rate, increased hunger hormones, and preferential fat regain 1
• Complete fasting creates "famine reactions" that drive rapid weight regain and can predispose to obesity long-term 1

Weight Regain Pattern

• After severe caloric restriction or fasting, weight regain is rapid and often exceeds initial weight 1
• The body prioritizes fat mass recovery over lean mass recovery during refeeding 1
• This creates a worse body composition than before fasting (more fat, less muscle) 1

Clinical Bottom Line

Complete fasting for 16 days is not a weight loss strategy—it is a medical emergency waiting to happen. The expected 16-24 pound loss comes at catastrophic cost to health, muscle mass, and metabolic function, with high risk of death from cardiac complications or refeeding syndrome. Any individual considering this must seek immediate medical evaluation and evidence-based weight management instead 2, 1.