Nutrition Science and Macronutrient Metabolism
What this domain tests
This domain checks whether you can convert food, substrate, and activity data into defensible energy and protein prescriptions, and whether you understand metabolic regulation rather than memorized numbers.
Core rules
- Atwater factors: carbohydrate 4 kcal/g, protein 4, fat 9, alcohol 7; fiber about 2 kcal/g in mixed diets and often counted as zero in simple calculations. Label rounding shifts values.
- Respiratory quotient: fat 0.70, protein 0.82, mixed diet 0.85, carbohydrate 1.00; RQ above 1.0 suggests lipogenesis or overfeeding.
- BMR is measured under strict conditions; RMR is less standardized. Mifflin–St Jeor is preferred for adults: women 10W + 6.25H − 5A − 161; men use +5. PAL 1.4 sedentary, 1.6–1.7 active.
- Protein: 0.8 g/kg/day for healthy adults; 1.0–1.5 g/kg in catabolism. Nine essential amino acids; leucine signals mTOR; nitrogen balance = intake − (urine urea nitrogen + 4 g).
- Fiber: 25–38 g/day; soluble fiber lowers LDL cholesterol; insoluble fiber improves transit.
Worked example
A 70 kg, 165 cm, 30-year-old woman with PAL 1.4. Mifflin BMR = 10(70) + 6.25(165) − 5(30) − 161 = 700 + 1031 − 150 − 161 = 1420 kcal. TEE = 1420 × 1.4 = 1988 kcal. A 25% deficit gives about 1490 kcal. Protein at 0.8 g/kg = 56 g. State whether you used actual or ideal body weight; in obesity, use adjusted or ideal weight only when your protocol specifies it.
Traps
Using 30 kcal/kg as if it were measured REE; assigning RQ 0.70 to a mixed meal; prescribing 0.8 g/kg to a septic patient; counting alcohol at 4 kcal/g; omitting units (kJ versus kcal); applying Harris–Benedict without naming the equation. Marks are lost when the equation, activity factor, and weight basis are not stated.