A Factorial Model of the Minimum Metabolic Demand for Protein and Indispensable Amino Acids in Young Adult Males:...

Consensus concerning human dietary protein and indispensable amino acid (IAA) recommendations is lacking. A factorial model capable of predicting the minimum metabolic demand (MMD) for protein and each IAA and elucidating underlying processes would provide valuable mechanistic insight.

The study aimed to provide an understanding of the basal metabolic demand for protein and each IAA in the adult human using a factorial approach.

A factorial model for the MMD for each AA and protein was developed by summing obligatory AA losses. Oxidative and gut endogenous losses have been given previously. Urinary free amino acids and peptides, hair, skin, nail, and miscellaneous losses, and losses because of functional roles and irreversible modification were estimated from the literature. MMD values were compared with current Food and Agriculture Organization/World Health Organization recommendations and used as reference patterns to calculate protein quality by the Digestible Indispensable Amino Acid Score.

The protein MMD was 634 mg/kgBW/d, close to the current Estimated Average Requirement (660 mg/kgBW/d). Isoleucine and leucine MMD values were also close to current recommendations (21 and 40 mg/kgBW/d, respectively), whereas other MMDs were increased by 15%-150%. Oxidative losses were the largest contributor to the MMD (54%-72%) followed by endogenous gut losses, particularly for threonine (33%). The MMD for total IAAs as a proportion of protein (41%) was close to that of body protein (42%) and almost 50% greater than current recommendations (28%). MMD-based protein quality scores were reduced compared with those based on current recommendations.

A factorial model for estimation of the MMD for protein and each IAA provides a mechanistic understanding of requirements and their sensitivity to metabolic processes. Each parameter is affected by variations in protein quantity and quality, and different physiological states. Additional data, when available, will enable model refinement.