Can undigested food proteins enter the bloodstream? [duplicate]

Question

I know that food proteins in our digestive system are denaturated and broken down into amino acids or very small peptides that are then absorbed in the small intestine. If some proteins stay undigested they move to the large intestine and either gut flora eats them or they are excreted.

But lately, I've been hearing a lot of stuff like "if you eat a lot of eggs there will be egg proteins in your blood" or "drink liquid collagen and it will travel to your skin through the blood". It seems really stupid to me. I imagine if all sorts of food proteins entered our blood they would wreak havoc there catalyzing random reactions, triggering immune responses, etc. So it cannot be a very frequent event. But I've been wondering if some of the food proteins can on occasion end up in the blood of relatively healthy people. Does this ever happen? With food allergens maybe?

Answer 1

Sort of.

Proteins can enter the body through the intestines by exploiting a few transport mechanisms, They are not truly crossing the cell membrane but are transported across the cell in vesicles. Though not into the bloodstream but into the lymph system.

M cells in particular will move antigens across the intestinal wall, a few more durable proteins (like prions) have been shown to piggyback on this system to cross in tiny quantities. Some viruses also exploit it. Collagen definitely does not enter this way but there are likely egg antigens that may.

Note this is very rare for non-antigens, the vast majority of food you eat will not contain anything that can exploit this although they may contain antigens that get passed to the immune system.

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Answer 2

That's impossible, if it has to pass through your cells membrane , check this small protein of 3 amino acids (Garcia, A., Eljack, N. D., Sani, M. A., Separovic, F., Rasmussen, H. H., Kopec, W., ... & Clarke, R. J. (2015). Membrane accessibility of glutathione. Biochimica et Biophysica Acta (BBA)-Biomembranes, 1848(10), 2430-2436.)

Although going through cells intermembrane... I think that's possible in theory, but even if that's happens so few protein concentration would reach other places.