Macronutrient metabolism by the human gut microbiome: major fermentation by-products and their impact on host health

Table 2 Major products of amino acid fermentation by the human gut microbiota

Amino acid	Amino acid class	Major products
Aspartate	Acidic	Propionate
Glutamate	Acidic	Acetate, Butyrate
Alanine	Aliphatic	Acetate, Propionate, Butyrate
Glycine	Aliphatic	Acetate Methylamine
Isoleucine	Aliphatic	2-Methylbutyrate or converted to Valine
Leucine	Aliphatic	Isovalerate
Proline	Aliphatic	Acetate
Valine	Aliphatic	Isobutyrate
Asparagine	Amidic	Converted to aspartate
Glutamine	Amidic	Converted to glutamate
Phenylalanine	Aromatic	Phenolic SCFA Phenylethylamine
Tryptophan	Aromatic	Indolic SCFA Tryptamine
Tyrosine	Aromatic	4-Hydroxyphenolic SCFA Tyramine
Arginine	Basic	Converted to other amino acids (mainly Ornithine) Agmatine
Histidine	Basic	Acetate, Butyrate Histamine
Lysine	Basic	Acetate, Butyrate Cadaverine
Serine	Hydroxylic	Butyrate
Threonine	Hydroxylic	Acetate, Propionate, Butyrate
Cysteine	Sulfur-containing	Acetate, Butyrate, Hydrogen sulfide
Methionine	Sulfur-containing	Propionate, Butyrate, Methanethiol

Listed are the compounds found to be above 1 mM concentration in in vitro fermentation experiments conducted by Smith and Macfarlane [92], in addition to the biogenic amines that can be produced by decarboxylation [12, 13]. Underlined are the products indicated as most abundant as reported in a review article by Fan et al. [12]

ISSN: 2049-2618