Entry of Peptides of Dietary Origin into the Circulation

Current theories of protein digestion and absorption state that free amino acids are the only significant form in which amino-N crosses the intestine and enters the systemic circulation. Nevertheless, there is now abundant evidence that intact peptides escaping digestion (or undergoing only partial digestion) and even whole protein molecules can enter the circulation in health and disease. Since peptides are now believed to play a major role in neural and endocrine regulation and in view of the fact that intestinal digestive activity can be reduced and intestinal ‘permeability’ increased in a variety of pathological conditions, the possibility that absorbed intact peptides can exert biological activities in peripheral tissues and can elicit symptoms in susceptible individuals now requires critical evaluation. These considerations may provide a physiological rationale for changing the source(s) of dietary protein in cases where food allergies/dietary sensitivities are suspected.