Hi Dr. Cordain,
I read the lysozyme article and I am wondering if you could please indicate if egg white lysozyme is more readily bio-available raw or cooked?
If egg whites are consumed by eating them raw or cooked, does the body actually have the ability to put it into bloodstream and utilize the lysozyme? In other words – what is the big deal if a human cannot even utilize it if it is digested and broken up or if it cannot be absorbed if raw or cooked?
How would evolution have made lysozyme more available – cooking, selection of egg type?
Thanks for your question regarding egg white lysozyme. Let me answer the issues you have brought up.
You can see from Table 1 below that egg white protein is no simple protein, but rather a conglomeration of multiple proteins which have been designed by natural selection to cause toxic effects in bacteria and microorganisms.
Table 1. Major proteins and their properties found in egg whites (adapted from references 1-5).
In a mouse model, boiling egg white proteins (EW) from five to 60 minutes increased the allergenicity of egg white lysozyme via abrogation of oral tolerance compared to the consumption of raw egg whites (6). Specific IgE, IgG1 and IgG antibody responses were suppressed by raw EW, but not by EW boiled for five or 60 minutes, fed prior to sensitization with 10 microg OVA (immunoreactive ovalbumin) or 1 microg DNP-OVA in alum (6). Similar results were obtained when mice were sensitized with 10 microg conalbumin, ovomucoid or lysozyme in alum. BALB/c spleen cell proliferation and secretion of Th2 cytokines IL-4 and IL-5 during in vitro stimulation with OVA were also suppressed by feeding raw EW, but not by boiled EW (6). This study suggests that boiling of EW may affect their intestinal antigen processing and thus prevent the induction of oral tolerance.
The bottom line
Cooking egg white proteins, including lysozyme, likely makes them more capable of producing allergy or autoimmunity. Am I suggesting that you should eat eggs raw? No! Gentle heat (poaching, low heat during hard boiling or scrambling of eggs) is preferable. Individuals with autoimmune disease and/or food allergies should be cautious when including cooked egg whites in their diet.
Indeed, after consumption, egg white lysozyme rapidly enters human circulation (7). Egg white lysozyme is actually an enzyme known as N-acetylhexosaminodase that is also found in many human tissues, including tears (8). The function of lysozyme in both egg whites and in human tears is to act as a potent bactericidal agent by binding and dissolving bacterial cell walls (8). Lysozyme is unusual among the major egg white proteins in that it has an alkaline isoelectric point (pI), which means that it can form strong complexes with other egg white proteins including ovomucin, ovalbumen and ovotransferrin (1, 8). Hence, even though lysozyme is a benign enzyme produced in our own bodies, when we eat egg white lysozyme, it may come as a compound attached to other egg white proteins foreign to our bodies.
In the human digestive tract, enzymes called proteases normally break down proteins into their constituent amino acids so that the amino acids can be absorbed across the intestines. Because egg white protein contains high concentrations of protease inhibitors (ovomucoid, ovoinhibitor, ovostatin, cystatin) (Table 1), the human gut proteases (trypsin and chymotrypsin primarily) are less effective in degrading egg white proteins, and lysozyme/egg white protein complexes. Additionally, lysozyme is stable in the acidic gut environment (8) and therefore arrives intact in the lower gastrointestinal tract.
So what’s wrong if lysozyme/egg white protein complexes aren’t dissolved by normal digestive processes? Normally, large multifaceted proteins such as these complexes don’t have a prayer of getting across the intestinal barrier and into the bloodstream where they can interact with the immune system. Once again, lysozyme is an unusual protein because it rapidly breeches the gut barrier and enters human circulation (7). Lysozyme and the complexes it forms with other egg white proteins can cross the gut barrier and may interact with the immune system. This is the likely mechanism by which lysozyme/egg white protein complexes may be involved with the initiation and promotion of both allergy and autoimmunity.
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