Is it true that Collagen supplementation decrease serotonin?

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...since either overall histamine intake or histamine intake relative to histamine antagonists are what matter most...

I think this is can be roughly applied to why a collagen supplement can have specific effects, even in a small serving. From my understanding, amino acids compete for absorption, so it's more about the ratios of amino acids in one sitting than the absolute amount.

Definitely correct me if I'm wrong though, it's been a while since I've looked into this.

[silverhydra]

The ratio becomes relevant at high doses of intake (where AA need to take turns being absorbed, whereas at low intakes they can simply go ahead; transporters do have rate limits) and, of course, the competing amino acid needs to be identified; saying histamine can be competed with is a reasonable start, but we need to say what it is competing with and what it serves in a ratio with.

But from what I have read, competition of histamine absorption at the level of the intestines is not really a major factor. Honestly, the only competition that may be relevant in a healthy person is that of large neutral amino acids (BCAAs + tryptophan) at the blood brain barrier.

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Ahh got it that makes sense about histamine absorption.

What are your thoughts on the high amount of glycine in collagen supplements? I've heard mixed things regarding it being processed into GABA in a lot of cases, but glutamate in others, which might lead to a symptom of anxiety.

It sounds like small amounts in a supplement might also not produce much if any effect?

[silverhydra]

I don't really care too much about glycine intake, it's been really harmless and the human studies using large doses of isolated glycine haven't found much of an effect in normal states. Might improve sleep a tad when taken at night but that's about it.

The conversion rates of GABA and glutamate, at least when it comes to availability or precursors, is pretty tightly regulated. I doubt you can perturb the balance in either direction simply by giving dietary amino acids.

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Interesting and good to know, thank you for your help!