Energy Balance
The relationship between kilojoules consumed and expended:
- Intake ≈ Expenditure: Weight tends to remain stable.
- Intake > Expenditure: Surplus may be stored → potential weight gain.
- Intake < Expenditure: Body draws on stores → potential weight loss.
This is simplified. Hormones, metabolic adaptation, genetics, sleep and stress also influence energy balance. Two individuals with identical intake may respond differently.
Estimated Daily Requirements
From Australian Nutrient Reference Values — population estimates, not individual prescriptions.
| Group | Sedentary (kJ) | Moderate (kJ) | Active (kJ) |
|---|---|---|---|
| Men 19–30 | ~10,000 | ~11,500 | ~13,500 |
| Men 31–50 | ~9,700 | ~11,200 | ~13,000 |
| Men 51–70 | ~9,000 | ~10,500 | ~12,200 |
| Women 19–30 | ~7,900 | ~9,100 | ~10,800 |
| Women 31–50 | ~7,600 | ~8,800 | ~10,400 |
| Women 51–70 | ~7,200 | ~8,400 | ~9,800 |
Conversion: 1 kcal = 4.184 kJ. Australian labels use kJ. 8,700 kJ ≈ 2,080 kcal.
Macronutrients
| Macro | AMDR (%) | kJ/g | Functions |
|---|---|---|---|
| Carbs | 45–65 | 17 (4 kcal) | Primary energy; brain fuel; fibre |
| Protein | 15–25 | 17 (4 kcal) | Tissue repair; enzymes; immune |
| Fat | 20–35 | 37 (9 kcal) | Hormones; energy store; vitamin absorption |
BMR Estimation
Basal Metabolic Rate — energy at complete rest for basic functions (breathing, circulation, cell repair). Typically 60–75 % of daily expenditure.
Mifflin-St Jeor Equation
- Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Activity Multipliers
| Level | Description | Factor |
|---|---|---|
| Sedentary | Desk job, minimal exercise | 1.2 |
| Lightly active | Light exercise 1–3 d/wk | 1.375 |
| Moderately active | Moderate exercise 3–5 d/wk | 1.55 |
| Very active | Hard exercise 6–7 d/wk | 1.725 |
| Extremely active | Very hard + physical job | 1.9 |
Example
A 35-year-old woman, 165 cm, 62 kg, moderately active:
- BMR = (10 × 62) + (6.25 × 165) − (5 × 35) − 161 = 620 + 1,031 − 175 − 161 = 1,315 kcal
- TDEE = 1,315 × 1.55 = ~2,038 kcal (≈ 8,527 kJ)
Approximate starting points only. Do not account for individual metabolic variation or medications. Consult an accredited dietitian for personalised guidance.
Practical Tips
- Prioritise whole foods: vegetables, fruits, grains, lean protein, legumes, nuts.
- Portion awareness over rigid counting.
- Include all five food groups (Australian Dietary Guidelines).
- Limit ultra-processed foods, added sugars, excess sodium.
- Eat mindfully — respond to hunger and fullness cues.