General reference tables and formulas for estimating daily energy requirements. These are approximations, not prescriptions.
Energy balance refers to the relationship between energy intake (kilojoules or calories consumed through food and drink) and energy expenditure (kilojoules or calories used by the body for basic functions, physical activity and digestion).
In Australia, energy is officially measured in kilojoules (kJ), though calories (kcal) are also widely used. The conversion is: 1 kcal ≈ 4.184 kJ.
Energy balance is a simplified model. Body weight regulation involves complex hormonal, genetic and behavioural factors that go beyond simple arithmetic. The figures below are starting-point estimates, not definitive targets.
The following table shows approximate daily energy requirements for Australian adults, based on age, sex and physical activity level, as referenced by the Australian National Health and Medical Research Council (NHMRC).
| Group | Sedentary (kJ/day) | Moderately Active (kJ/day) | Active (kJ/day) |
|---|---|---|---|
| Men 19–30 years | ~10 000 | ~11 500 | ~13 500 |
| Men 31–50 years | ~9 500 | ~11 000 | ~13 000 |
| Men 51–70 years | ~8 800 | ~10 200 | ~12 000 |
| Women 19–30 years | ~7 900 | ~9 000 | ~10 500 |
| Women 31–50 years | ~7 500 | ~8 600 | ~10 000 |
| Women 51–70 years | ~7 000 | ~8 100 | ~9 500 |
Basal Metabolic Rate is the energy your body uses at rest for basic functions such as breathing, circulation and cell repair. It accounts for the majority of total daily energy expenditure in most people.
The Mifflin-St Jeor equation is one commonly used formula for estimating BMR. It has been found to be reasonably accurate in many studies, though individual variation remains significant.
| Sex | Formula (using kg and cm) |
|---|---|
| Men | BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5 |
| Women | BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161 |
To estimate total daily energy expenditure, BMR is multiplied by an activity factor:
| Activity Level | Multiply BMR by |
|---|---|
| Sedentary (little or no exercise) | 1.2 |
| Lightly active (1–3 days/week) | 1.375 |
| Moderately active (3–5 days/week) | 1.55 |
| Very active (6–7 days/week) | 1.725 |
| Extra active (very intense/physical job) | 1.9 |
The Australian NHMRC provides Acceptable Macronutrient Distribution Ranges (AMDR) for adults, expressed as a percentage of total energy intake:
| Macronutrient | AMDR (% of total energy) | Role |
|---|---|---|
| Protein | 15–25% | Muscle repair, immune function, enzyme production |
| Fat | 20–35% | Hormone production, nutrient absorption, energy storage |
| Carbohydrates | 45–65% | Primary energy source, brain function, fibre intake |
These ranges provide flexibility to accommodate different dietary preferences and health needs. The optimal distribution within these ranges depends on individual factors and goals, and should ideally be determined with professional guidance.
| Macronutrient | Energy per gram (kcal) | Energy per gram (kJ) |
|---|---|---|
| Protein | 4 kcal | ~17 kJ |
| Carbohydrates | 4 kcal | ~17 kJ |
| Fat | 9 kcal | ~37 kJ |
| Alcohol | 7 kcal | ~29 kJ |