The Three Macronutrients
Food energy comes from three macronutrients — protein, carbohydrates and fats — plus alcohol. Each provides a different amount of energy per gram:
| Macronutrient | Energy (kcal/g) | Energy (kJ/g) | Primary Roles |
|---|---|---|---|
| Protein | 4 | 17 | Muscle repair, enzyme production, immune function |
| Carbohydrate | 4 | 17 | Primary fuel for brain and high-intensity activity |
| Fat | 9 | 37 | Hormone production, cell membrane integrity, nutrient absorption |
| Alcohol | 7 | 29 | No essential physiological role |
How Much Protein Do You Need?
The Australian Recommended Dietary Intake (RDI) for protein is 0.84 g per kilogram of body weight per day for adult men and 0.75 g/kg/day for adult women. However, research suggests that physically active individuals may benefit from higher intakes — typically in the range of 1.2–2.0 g/kg/day — to support muscle protein synthesis and recovery.
Protein intake should be distributed across meals rather than consumed in a single sitting. Current evidence suggests that 20–40 g of protein per meal is sufficient to maximally stimulate muscle protein synthesis in most individuals.
Protein Content of Common Foods
| Food | Portion | Protein (g) | kcal |
|---|---|---|---|
| Chicken breast (grilled) | 120 g | 37 | 198 |
| Atlantic salmon | 125 g | 28 | 260 |
| Greek yoghurt (plain) | 170 g | 15 | 150 |
| Whole eggs | 2 large | 12.6 | 144 |
| Tinned tuna (in water) | 95 g tin | 20 | 95 |
| Red lentils (cooked) | 150 g | 13.5 | 172 |
| Tofu (firm) | 150 g | 18 | 130 |
| Lean beef mince | 100 g cooked | 26 | 180 |
Carbohydrates: Not All Equal
Carbohydrates are classified by their structure and how quickly they raise blood glucose. Complex carbohydrates (found in whole grains, legumes, starchy vegetables) generally provide sustained energy and contain more fibre than simple carbohydrates (found in sugar, juice, confectionery). The Australian Dietary Guidelines recommend choosing mostly whole-grain and high-fibre options.
For active individuals, carbohydrate intake supports training performance and glycogen replenishment. Requirements vary based on training volume and intensity — ranging from approximately 3 g/kg/day for light activity up to 8–12 g/kg/day for endurance athletes in heavy training.
Dietary Fats
Fats are essential for hormone production, absorption of fat-soluble vitamins (A, D, E, K) and providing structural components for cell membranes. The type of fat matters more than the total amount in most dietary contexts:
- Unsaturated fats (olive oil, avocado, nuts, oily fish) — generally associated with positive cardiovascular outcomes when replacing saturated fats.
- Saturated fats (butter, coconut oil, fatty cuts of meat) — current guidelines recommend limiting intake to less than 10% of total energy.
- Trans fats (some processed foods, partially hydrogenated oils) — associated with negative health outcomes; best minimised or avoided.
Reading Australian Food Labels
In Australia, the Nutrition Information Panel (NIP) on packaged foods displays energy (kJ), protein, fat (total and saturated), carbohydrate (total and sugars), and sodium per serving and per 100 g. Comparing values per 100 g allows more meaningful comparisons between products regardless of serving size differences.