I am most certainly not an expert, and my first reaction was to associate serotonin with the nervous system and not the digestive system. BUT THEN, I did a little research online, and found this interesting article entitled, Serotonin - Metabolism http://www.pharmacorama.com/en/Sections/Serotonin_2_1.php. It is very scientific in nature, but I did find the following section interesting, and I quote,
Serotonin is found in many tissues:
The half-life of serotonin is long in platelets and intestine, and very short, a few minutes, in the brain. The concentration of a compound in an organ, static view of a dynamic phenomenon, is not necessarily a good representation of metabolic activity and turn-over.
Melatonin found in plasma is released from the pineal gland. Its plasma concentration decreases during ageing.
(end of quote)
I wonder if this has ever been looked at before by the scientific community in relation to body odor.
If you want to research this further, you can go to your search engine and type the following keywords,
"serotonin" + "metabolism" + "digestion"
and you'll find articles that have these three words in them.