Definition
Body composition = the breakdown of your body into fat mass and lean mass (muscle, bone, organs, water).
Two people at 180 lbs can look completely different:
- Person A: 15% body fat = 27 lbs fat, 153 lbs lean
- Person B: 30% body fat = 54 lbs fat, 126 lbs lean
This is why body composition matters more than weight.
Why It Matters
Weight fluctuates 2-5 lbs daily from water, food, and hormones.
BMI is flawed — it can't distinguish a muscular athlete from someone with excess fat.
Body composition shows real progress — you can gain 5 lbs of muscle while losing 5 lbs of fat. Scale shows nothing; body composition shows transformation.
Types of Body Fat
Essential fat (required for survival):
- Men: 2-5%
- Women: 10-13%
Storage fat (what you're trying to lose):
- Subcutaneous: under skin, less dangerous
- Visceral: around organs, linked to disease
How to Measure
| Method | Accuracy | Cost |
|---|---|---|
| DEXA scan | ±1-2% | $100-150 |
| Bod Pod | ±2-3% | $50-100 |
| Bioimpedance scales | ±4-6% | $30-200 |
| AI photo analysis | ±2-4% | Free |
Healthy Ranges
| Category | Men | Women |
|---|---|---|
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Healthy | 18-24% | 25-31% |
How to Improve It
- Moderate calorie deficit (300-500 cal)
- High protein (0.8-1g per lb bodyweight)
- Strength training 3-4x per week
- Sleep 7-9 hours
This approach is called body recomposition — simultaneously building muscle while losing fat.