Energy Balance and Body Composition
What this domain tests
Energy Balance and Body Composition tests your ability to estimate total daily energy expenditure, set defensible calorie targets, interpret body composition methods, and explain why scale weight is not the same as fat loss.
Core rules
- TDEE = BMR + thermic effect of food + exercise activity thermogenesis + nonexercise activity thermogenesis.
- Mifflin–St Jeor: men = 10W + 6.25H − 5A + 5; women = 10W + 6.25H − 5A − 161, with W in kg, H in cm, A in years.
- Activity multipliers: sedentary 1.2, light 1.375, moderate 1.55, very active 1.725, extra active 1.9.
- A 500 kcal/day deficit is often used to target about 0.45 kg/week, but the 3,500 kcal per pound rule overestimates long-term loss because of adaptive thermogenesis and lean mass loss.
- BMI screens populations but misclassifies muscular clients and does not measure body fat. Skinfolds, BIA, and DEXA estimate composition with different error rates.
Worked example
A 35-year-old woman weighs 70 kg and is 165 cm tall. BMR = 10(70) + 6.25(165) − 5(35) − 161 = 700 + 1,031.25 − 175 − 161 = 1,395 kcal. With a moderate activity multiplier: 1,395×1.55 = 2,162 kcal. A 500 kcal deficit gives about 1,662 kcal/day and an expected loss near 0.45 kg/week, assuming adherence and no major metabolic adaptation.
Traps that cost marks
Applying the 3,500 kcal rule as if it were linear, overestimating activity level, interpreting a 1–2 kg scale change as pure fat, and using BMI alone to diagnose obesity or health status.