Nutrition Fundamentals: Nutrients, Digestion and Dietary Guidelines
What you must understand
SACE Stage 2 Nutrition rewards precise knowledge of the six nutrient classes - carbohydrates, proteins, lipids, vitamins, minerals and water - and of dietary fibre, which is not strictly a nutrient but is examined alongside carbohydrates. Know each nutrient's energy yield (carbohydrate 17 kJ/g, protein 17 kJ/g, lipid 37 kJ/g, alcohol 29 kJ/g), its main food sources, and its physiological roles: energy provision, growth and repair, regulation of body processes, and protection against deficiency disease. Distinguish macronutrients from micronutrients, and fat-soluble vitamins (A, D, E, K) from water-soluble ones (B group, C), because solubility drives absorption, storage and toxicity risk.
Be able to outline digestion and absorption: mechanical and chemical breakdown, the roles of amylase, protease and lipase, the sites where each acts, and where absorption occurs. Link this to nutrient bioavailability - for example, vitamin C enhancing non-haem iron absorption and phytates inhibiting it.
Traps in questions
- Confusing energy density with nutrient density: a food can be energy-dense yet nutrient-poor.
- Assuming a high-protein food is automatically a complete protein; completeness depends on amino acid profile.
- Mixing up deficiency diseases, such as beriberi (thiamin) versus pellagra (niacin).
- Forgetting that dietary guidelines are population recommendations, not individual prescriptions.
Worked example - rule of thumb
A snack provides 12 g carbohydrate, 5 g protein and 4 g lipid. Energy = (12 × 17) + (5 × 17) + (4 × 37) = 204 + 85 + 148 = 437 kJ. Expressing each nutrient's contribution as a percentage shows the lipid contributes the largest share (about 34%) despite the smallest mass - a common exam insight.
Key points
- Apply the correct Atwater factors: 17, 17, 37 and 29 kJ/g.
- Match each nutrient to its roles, sources and deficiency outcomes.
- Explain digestion enzymes and absorption sites accurately.
- Distinguish energy density from nutrient density.
- Use the Australian Dietary Guidelines as population-level advice.