Energy Balance Basics
Energy balance is the relationship between kilojoules consumed and expended:
- Intake ≈ Expenditure: Weight tends to remain stable.
- Intake > Expenditure: Surplus may be stored, potentially leading to weight gain.
- Intake < Expenditure: Body draws on stores, potentially leading to weight loss.
This is simplified. Energy balance is also influenced by hormones, metabolic adaptation, genetics, sleep, stress and the thermic effect of food. Individual responses to identical intake can differ considerably.
Estimated Daily Requirements (Australia)
From Australian Nutrient Reference Values — 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 (%) | kJ/g | Key Functions |
|---|---|---|---|
| Carbohydrates | 45–65 | 17 (4 kcal) | Primary energy; brain fuel; fibre for digestion |
| Protein | 15–25 | 17 (4 kcal) | Tissue repair; enzymes; hormones; immune support |
| Fat | 20–35 | 37 (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 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 (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 30-year-old woman, 170 cm, 68 kg, moderately active:
- BMR = (10 × 68) + (6.25 × 170) − (5 × 30) − 161 = 680 + 1,062.5 − 150 − 161 = 1,431.5 kcal
- TDEE = 1,431.5 × 1.55 = ~2,219 kcal (≈ 9,284 kJ)
Formulas provide approximate starting points only. They do not account for individual metabolic variation, body composition or medications. Consult an accredited practising dietitian for personalised guidance.
Practical 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 Australian Dietary Guidelines.
- Limit ultra-processed foods, added sugars and excess sodium.
- Eat mindfully — respond to hunger and fullness cues.