Amount and fate of egg protein escaping assimilation in the small intestine of humans

Studies attempting to evaluate protein assimilation in humans have hitherto relied on either ileostomy subjects or intubation techniques. The availabi lity of stable isotope-labeled protein allowed us to determine the amount a nd fate of dietary protein escaping digestion and absorption in the small i ntestine of healthy volunteers using noninvasive tracer techniques. Ten hea lthy volunteers were studied once after ingestion of a cooked test meal, co nsisting of 25 g of C-13-, N-15-, and H-2-labeled egg protein, and once aft er ingestion of the same but raw meal. Amounts of 5.73% and 35.10% (P < 0.0 05) of cooked and raw test meal, respectively, escaped digestion and absorp tion in the small intestine. A significantly higher percentage of the malab sorbed raw egg protein was recovered in urine as fermentation metabolites. These results 1) confirm that substantial amounts of even easily digestible proteins may escape assimilation in healthy volunteers and 2) further supp ort the hypothesis that the metabolic fate of protein in the colon is affec ted by the amount of protein made available.