Understanding Energy Balance
Energy balance is the relationship between kilojoules consumed and kilojoules expended:
- Intake ≈ Expenditure: Weight tends to remain stable.
- Intake > Expenditure: Surplus energy may be stored, potentially leading to weight gain.
- Intake < Expenditure: Body draws on stores, potentially leading to weight loss.
This is a simplification. Energy balance is also influenced by hormones, metabolic adaptation, genetics, sleep, stress and the thermic effect of different foods. Individual responses to the same intake can vary considerably.
Estimated Daily Energy Requirements (Australia)
Values derived from Australian Nutrient Reference Values. These are population-level estimates — not individual prescriptions.
| Group | Sedentary (kJ/day) | Moderate (kJ/day) | Active (kJ/day) |
|---|---|---|---|
| Men 19–30 yrs | ~10,000 | ~11,500 | ~13,500 |
| Men 31–50 yrs | ~9,700 | ~11,200 | ~13,000 |
| Men 51–70 yrs | ~9,000 | ~10,500 | ~12,200 |
| Women 19–30 yrs | ~7,900 | ~9,100 | ~10,800 |
| Women 31–50 yrs | ~7,600 | ~8,800 | ~10,400 |
| Women 51–70 yrs | ~7,200 | ~8,400 | ~9,800 |
Conversion: 1 kcal = 4.184 kJ. Australian labels use kJ. Example: 8,700 kJ ≈ 2,080 kcal.
Macronutrients
| Macronutrient | AMDR (% energy) | kJ per gram | Key Functions |
|---|---|---|---|
| Carbohydrates | 45–65 % | 17 kJ (4 kcal) | Primary energy; brain fuel; fibre for digestive health |
| Protein | 15–25 % | 17 kJ (4 kcal) | Tissue repair; enzymes; hormones; immune support |
| Fat | 20–35 % | 37 kJ (9 kcal) | Energy storage; hormones; vitamin A, D, E, K absorption |
Basal Metabolic Rate (BMR)
BMR is the estimated energy needed at complete rest for basic physiological functions. It typically accounts for 60–75 % of daily expenditure.
Mifflin-St Jeor Equation
- Men: BMR (kcal) = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: BMR (kcal) = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Activity Multipliers (TDEE = BMR × Factor)
| Level | Description | Factor |
|---|---|---|
| Sedentary | Desk job, minimal exercise | 1.2 |
| Lightly active | Light exercise 1–3 days/wk | 1.375 |
| Moderately active | Moderate exercise 3–5 days/wk | 1.55 |
| Very active | Hard exercise 6–7 days/wk | 1.725 |
| Extremely active | Very hard exercise + physical job | 1.9 |
Worked Example
A 40-year-old man, 178 cm, 82 kg, moderately active:
- BMR = (10 × 82) + (6.25 × 178) − (5 × 40) + 5 = 820 + 1,112.5 − 200 + 5 = 1,737.5 kcal
- TDEE = 1,737.5 × 1.55 = ~2,693 kcal (≈ 11,270 kJ)
Estimation formulas are approximate starting points. They do not account for individual metabolic variation, body composition or medications. For personalised guidance, consult an accredited practising dietitian.
Practical Balanced-Eating Tips
- Prioritise whole foods: vegetables, fruits, whole grains, lean protein, legumes, nuts, seeds.
- Focus on portion awareness rather than rigid counting.
- Include all five food groups per the Australian Dietary Guidelines.
- Limit ultra-processed foods, added sugars and excess sodium.
- Eat mindfully — respond to hunger and fullness cues.