Nitrogen Balance

Nitrogen balance is an accounting method. Because protein is about 16 percent nitrogen, a gram of nitrogen corresponds to roughly 6.25 grams of protein, so intake is estimated from diet and losses from urinary urea nitrogen plus fixed allowances for faecal and dermal routes. A positive balance means the body retained nitrogen and, by inference, accrued protein; a negative balance means net loss, as in burns, sepsis, immobilisation or energy deficit. It is a whole-body figure and says nothing about which tissue changed.

It is the oldest quantitative evidence that growth hormone is anabolic. Short studies in healthy adults, catabolic surgical patients and growth hormone deficiency reliably shift nitrogen balance positive within days, alongside falls in urea production. That evidence drove decades of interest in growth hormone for critical illness, which ended when a large multicentre trial in critically ill patients reported increased mortality rather than improved recovery.

As a decision variable, nitrogen balance is a short-horizon marker of direction, not magnitude or outcome. It detects an intervention's effect over days, which no measure of muscle mass can do, and that speed is its value in metabolic ward studies. What it cannot do is tell you whether retained nitrogen became contractile protein, connective tissue, or visceral protein, or whether anything functional followed.

This is where growth hormone claims most often overreach. Nitrogen retention under growth hormone is accompanied by sodium and water retention, so early gains in lean body mass measured by bioimpedance or DXA are substantially fluid, and the well-documented oedema and carpal tunnel symptoms come from the same physiology. Trials measuring strength and performance rather than lean mass have generally not shown the improvement the nitrogen data appear to promise.