Weight Loss Guide
3-Day Fast Weight Loss: How Much Will You Actually Lose?
Most people lose 4-7 pounds during a 72-hour fast — but how much is fat vs water? Here's the honest breakdown of what to expect and why the scale doesn't tell the whole story.
Quick Answer
The Math: Where Does the Weight Go?
When you step on the scale after a 72-hour fast, the number will be lower — but understanding what that number represents is crucial for setting realistic expectations.
Water & Glycogen
3-5 lbsYour liver and muscles store about 500g of glycogen, and each gram binds 3g of water. When you deplete glycogen during fasting, you release 4-7 lbs of water weight. This returns when you eat carbohydrates again — it's not "gaining weight back," it's normal physiology.
Actual Fat Loss
1-2 lbsYou burn approximately 2,000-2,500 calories per day at rest. Over 72 hours, that's 6,000-7,500 calories, or roughly 1.7-2.1 lbs of body fat. This is the actual fat you lose — and it stays off (assuming you don't overeat after).
Gut Contents
1-2 lbsYour digestive system typically holds 1-2 lbs of food at any given time. After 72 hours with no food, this is eliminated. Like water weight, this returns when you eat again.
What People Actually Report
Based on hundreds of fasting reports and studies, here's the typical range:
| Starting Weight | Typical Loss | Fat Loss |
|---|---|---|
| Under 150 lbs | 3-5 lbs | ~1 lb |
| 150-200 lbs | 5-7 lbs | ~1.5 lbs |
| 200-250 lbs | 6-9 lbs | ~2 lbs |
| Over 250 lbs | 7-12 lbs | ~2.5 lbs |
Important Context
Individual results vary significantly based on starting weight, activity level, metabolic rate, and how much glycogen you had stored. Men typically lose more than women due to higher muscle mass and metabolic rate.
Why the Scale Will "Lie" to You
After Breaking Your Fast
You'll likely "gain" 2-4 lbs within 24-48 hours of eating again. Don't panic — this is glycogen and water refilling, plus food in your gut. The fat you lost is still gone.
The True Result
Wait 5-7 days after your fast to assess your "true" weight loss. Once water and glycogen stabilize, you'll see the real fat loss — typically 1-2 lbs lower than your pre-fast weight.
Better Metrics Than Scale Weight
Consider tracking waist circumference, how clothes fit, progress photos, or body composition (if you have access to DEXA scans). These give a more accurate picture than scale weight alone.
Is a 72-Hour Fast Good for Weight Loss?
Honestly? A single 72-hour fast isn't primarily a weight loss tool. Losing 1-2 lbs of fat is nice, but you could achieve similar fat loss with a week of moderate calorie restriction.
The real weight loss benefits of extended fasting are:
- ✓Improved insulin sensitivity — makes long-term weight management easier
- ✓Metabolic flexibility — your body becomes better at burning fat
- ✓Reset your appetite — many find cravings reduced after fasting
- ✓Break plateaus — can help restart stalled weight loss
- ✓Psychological shift — changes your relationship with hunger and food
The Bottom Line
Don't do a 72-hour fast purely for the scale number. Do it for the metabolic reset, autophagy, and mental clarity. The fat loss is a bonus, not the main event.
Tips to Maximize Fat Loss During Your Fast
Light Walking
20-30 min walks help mobilize fat stores without excessive stress
Black Coffee
Caffeine increases fat oxidation and suppresses appetite
Cold Exposure
Cold showers may increase brown fat activation and calorie burn
Sleep Well
Poor sleep increases cortisol, which promotes fat retention
Low-Carb Refeeding
Breaking your fast low-carb extends fat-burning mode
Don't Rush Back
Avoid immediately returning to high-carb eating patterns
Common Questions
Will I gain it all back?
You'll regain 2-4 lbs of water and glycogen — that's unavoidable and normal. The 1-2 lbs of fat loss is permanent, assuming you don't overeat after the fast.
Does fasting slow metabolism?
Short-term fasting (72 hours) actually increases metabolic rate slightly due to norepinephrine release. Extended fasting beyond 3-5 days may slow metabolism. This is one reason 72 hours is considered optimal.
Will I lose muscle?
Minimal muscle loss occurs during 72 hours. Growth hormone increases up to 5x specifically to preserve muscle. Your body preferentially burns fat. Studies show lean mass is largely preserved during short fasts.
How often can I fast for weight loss?
Most people do monthly 72-hour fasts. More frequent extended fasting isn't necessarily better and may lead to nutrient deficiencies. For ongoing weight management, intermittent fasting (16:8, etc.) is more sustainable.
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