Nitrogen balance studies used to establish the RDA for protein are prone to errors due to incomplete collection and overestimation of nitrogen losses.
"The original studies that led to the derivation of the Recommended Dietary Allowance are what we call nitrogen balance... Those studies we've known for a long time are problematic because of incomplete collection, overestimation, etc., of losses." (said at 0:15:48)
While dietary reference values (such as the Recommended Dietary Allowance) for protein were historically established using nitrogen balance studies, the speaker states the direction of the methodological error backwards. In classical nitrogen balance studies, incomplete collection of urine/feces and unmeasured miscellaneous routes (such as sweat, hair, skin desquamation, and flatus) lead to an underestimation of nitrogen losses (output) and an overestimation of intake, resulting in an artificially positive balance and potential underestimation of true protein requirements, rather than an overestimation of losses.
- contradicts: Uses and limitations of the balance technique. (JPEN. Journal of parenteral and enteral nutrition 1987)
"The errors tend to overestimate intake and underestimate output, thereby leading to erroneously positive balances. These errors include losses of food on cooking and eating utensils and dishware, losses of feces or urine on toilet paper or in collection containers, and losses through sweat, exfoliated skin, hair and nail growth, saliva, menses, blood sampling, toothbrushing, semen, and, for nitrogen, from flatus and respiration." (abstract, results, passage verified)
pubmedfull study (doi) - supports: The indicator amino acid oxidation (IAAO) technique: a novel approach to assess protein in… (Critical reviews in food science and nutrition 2026)
"Protein intakes to meet the dietary requirement (the Recommended Daily Allowance, RDA; 0.83 g protein·kg BM -1 ·d -1 ) were determined using nitrogen balance methodology." (abstract, results, passage verified)
pubmedfull study (doi)