Nutrition Assessment and Body Composition
Nutrition Assessment and Body Composition
This domain covers dietary assessment methods, anthropometry, body composition techniques, and interpretation. The exam tests reliability, validity, and appropriate use of BMI, skinfolds, bioelectrical impedance, and DXA.
Core rules
- Dietary assessment: 24-hour recall is quick but relies on memory; food frequency questionnaires capture usual intake but lack detail; weighed food records are detailed but can alter behavior. Use multiple methods when possible.
- BMI is a population screening tool; it misclassifies muscular athletes as overweight and does not measure body fat.
- Skinfolds estimate subcutaneous fat; technique and technician error matter. Use the same technician and protocol for tracking.
- Bioelectrical impedance (BIA) is affected by hydration, recent exercise, food, and menstrual status.
- DXA provides regional fat and lean mass but still has assumptions and radiation exposure.
- Track fat-free mass and performance, not just scale weight.
Worked example
A 75 kg athlete has 15% body fat. Fat mass = 0.15 × 75 = 11.25 kg; fat-free mass = 63.75 kg. If the goal is 12% body fat while preserving fat-free mass, target weight = 63.75 ÷ 0.88 = 72.4 kg. The athlete needs to lose about 2.6 kg of fat. Reasoning: calculate from fat-free mass, not from scale weight alone; this protects lean mass and sets a realistic target.
Traps
Using BMI to judge a strength athlete; comparing skinfolds taken by different technicians; treating BIA as precise; and ignoring that dehydration can make body composition results look leaner.