Both the quality and the quantity of dietary amino acids is important:
- essential amino acids should constitute at least half of the dietary intake
- meat proteins contain suitable proportions of essential and non-essential amino acids
- vegetable proteins may be deficient in sulphur-containing amino acids; vegans and vegetarians may need dietary supplementation
- quantity; dependent on the balance against utilization and losses:
- healthy adult: a minimum of 0.5 g/kg weight per day is required. This rises to 1 g/kg/day with average daily function.
- pregnancy: increased demands for fetal growth and support; up to 1.5 g/kg/day.
- growing child: up to 2.5 g/kg/day.
The nitrogen balance is a simple index of whether protein requirements are being met.