Nutrition Principles
What to know
Expect questions on the six nutrient classes (carbohydrate, protein, fat, vitamins, minerals, water), their energy yields (carbohydrate 4 kcal/g, protein 4 kcal/g, fat 9 kcal/g, alcohol 7 kcal/g), and their primary functions. Know the macronutrient Acceptable Macronutrient Distribution Ranges (AMDR): carbohydrate 45–65%, protein 10–35%, fat 20–35% of energy for adults. Understand the Dietary Reference Intakes family: Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), Adequate Intake (AI), and Tolerable Upper Intake Level (UL).
Be solid on digestion and absorption basics: carbohydrate digestion begins in the mouth with salivary amylase, protein in the stomach with pepsin, and fat emulsified by bile with absorption into lymph via chylomicrons. Know the difference between water-soluble and fat-soluble vitamins, and that fat-soluble vitamins (A, D, E, K) carry toxicity risk at high intakes.
Traps
- Mixing up the RDA (covers ~97–98% of healthy people) with the EAR (median requirement) or AI (used when data are insufficient).
- Forgetting that fiber contributes little energy because it is largely unabsorbed.
- Assuming a "natural" nutrient is safer; the UL applies regardless of source.
- Confusing glycemic index (how fast a food raises blood glucose) with glycemic load (which accounts for portion).
Rule of thumb
For energy math, use the 4-4-9 rule and check that percentages sum to 100. If a label gives grams, multiply before dividing by total calories.
Worked example: A 2,000 kcal diet with 75 g protein, 250 g carbohydrate, and 67 g fat yields 300 + 1,000 + 603 = 1,903 kcal. Protein is 300/1,903 ≈ 16%, carbohydrate ≈ 53%, fat ≈ 32%-all within AMDR ranges.