Can elevated digestive enzyme need with low urinary anserine reflect impaired protein digestion or assimilation?

In clinical nutrition and gastroenterology, assessing protein digestion and assimilation involves evaluating pancreatic function and protein-derived dietary biomarkers. This assessment synthesizes the relationship between digestive enzyme requirements and the urinary excretion of the dietary dipeptide anserine.

Clinical evidence and diagnostic utility

• Impaired protein digestion or assimilation, such as in pancreatic exocrine insufficiency (EPI), is characterized by insufficient endogenous proteolytic activity, establishing a clear clinical need for exogenous digestive enzyme replacement therapy.
• In contrast, utilizing urinary anserine to diagnose digestive impairment lacks clinical validation. Standard diagnostic guidelines rely on established markers like fecal elastase rather than urinary dipeptides.

Mechanistic pathways of anserine absorption

• Dietary anserine, primarily found in meat and poultry, is absorbed intact in the small intestine via the proton-coupled peptide transporter 1 (PEPT1). A dose-dependent fraction of this absorbed dipeptide is subsequently excreted in the urine.
• Mechanistically, impaired luminal digestion of meat proteins could reduce the release of free anserine from the food matrix, thereby limiting PEPT1-mediated absorption and lowering urinary recovery. This physiological pathway makes the connection between maldigestion and low urinary anserine biologically plausible.

Confounding factors in clinical practice

• In practice, urinary anserine primarily reflects recent dietary consumption of poultry and meat rather than overall digestive capacity.
• Furthermore, urinary excretion levels are heavily confounded by substantial inter-individual variability in renal handling and the activity of serum carnosinase-1, the enzyme responsible for hydrolyzing the dipeptide.

Bottom line

• Bottom line: While a mechanistic link between impaired protein digestion and reduced urinary anserine excretion is plausible, urinary anserine is not a clinically validated biomarker for malassimilation and is highly confounded by recent dietary protein intake and individual carnosinase-1 activity.