A calorie deficit occurs when energy intake is less than total daily energy expenditure (TDEE). The body responds by oxidising stored energy — primarily fat. Approximately 7,700 kcal deficit = 1 kg of fat lost. A 500 kcal/day deficit produces approximately 0.5 kg/week. Deficits above 750 kcal/day risk muscle loss, hormonal disruption and metabolic adaptation. The maximum sustainable fat loss rate is approximately 0.5-1% of bodyweight per week. Adequate protein (1.6-2.2g/kg) is essential to preserve muscle during a deficit.
Key points
- Energy intake < TDEE = fat loss
- ~7,700 kcal deficit per kg fat
- 500 kcal/day deficit = ~0.5kg/week
- Protein 1.6-2.2g/kg preserves muscle