Nitrogen balance

The nitrogen balance is a simple index of whether physiological protein requirements are being met. Urinary urea is taken as a rough indicator of protein degradation and loss from the body. Oral protein intake is quantified. Protein and urea are assumed to be rough indices of physiological nitrogen.

A negative nitrogen balance occurs when urinary nitrogen losses are greater than oral nitrogen intake. It may occur in:

• malnutrition e.g lack of essential amino acid - other amino acids which would have gone into the making of a new protein with the absent essential amino acid are instead degraded
• starvation
• adrenocortical steroid therapy

A positive nitrogen balance occurs when urinary losses are less than intake. It may occur in:

• active growth
• healing after systemic insult

Both positive and negative nitrogen balances are indications for dietary supplementation after a full assessment of which particular amino acids are deficient, with or without treatment of any underlying cause.