Short- & Medium-chain Fatty Acids Consumption

KEY Fermenters: Oxidation or fermentation by gut bacteria producing acid; Use: Utilisation or assimilation by gut bacteria; Common: Combined use and O/F for widespread, moderate and minor gut colonisers (total bacteria: 500);

SCFA	Common	Species examples	All consumers	Prevalence in food	Human digestion, metabolism, interactions	Structure
Formate	9	Bacillus licheniformis; Blautia hydrogenotrophica; Campylobacter concisus; Campylobacter gracilis; Campylobacter ureolyticus; Desulfitobacterium hafniense; Desulfovibrio desulfuricans;	96	Detected in fruits (typically low mg/100g), honey, vegetables (onions: 45 mg/100g) and nettles.	Readily absorbed and metabolised, although high quantities can result in acidosis, optic nerve damage and kidney damage.
Acetate	35	Anaerobutyricum hallii; Anaerostipes caccae; Anaerostipes hadrus; Butyricicoccus pullicaecorum; Butyrivibrio fibrisolvens; Citrobacter farmeri; Citrobacter freundii;	336	Found naturally in apples, grapes and other fruits, and is added to numerous other foods (vinegar, soy sauce). Produced during oxidative fermentation of alcoholic foodstuffs.	Normal levels of acetic acid are rapidly absorbed and metabolised to acetyl-CoA, while high serum levels (~2 mM) results in excretion in the urine (Richards1982).
Propionate	8	Bacillus licheniformis; Citrobacter farmeri; Citrobacter koseri; Enterobacter hormaechei subsp. hormaechei; Gordonibacter urolithinfaciens; Hungatella effluvii; Micrococcus luteus;	181	Food additive to breads, pastas, processed vegetables and cheeses.	Propionate as an additive has been linked to weight gain, whereas microbiome-produced propionate helps regulate appetite and blood glucose, and reduces inflammation. Propionate is converted to glucose in the liver (Jones2016).
Butyrate	3	Allisonella histaminiformans; Desulfitobacterium hafniense; Paraclostridium bifermentans;	84	Found in fermented foods, such as yoghurt, hard cheeses and sauerkraut. Also butter and cow's milk (ester). Prebiotic foods such as resistant starches and pectin promote butyrate formation in the gut.	Butyrate is used as a major source of energy for colonocytes. It is easily absorbed (not in chylomicrons) and can also be metabolised by the liver, producing acetyl-CoA, and products derived from this intermediate.
Isobutyrate	0		28	Detected in carob, vanilla and the roots of some herbs, or as ester derivatives in other plants. Brown beans and proteinaceous material are a prebiotic source for IBA.	IBA has been linked to improve glucose sensitivity and may effect adipocyte lipid metabolism.
Valerate	2	Selenomonas ruminantium; Stenotrophomonas maltophilia;	62	Found in Valeriana plant species and cocoa, but generally considered a minor metabolite of the gut microbiome.	Tests in Sprague-Dawley rats demonstrated reduced blood pressure, cardio protection and reduced intraocular pressure, suggesting valerate is readily absorbed (not encapsulated in chylomicrons) and is deeply penetrating (Skrzypecki2020).
Isovalerate	0		29	Present in fermented foods, such as Swiss cheese and some beers, and is produced as a metabolite by the gut microbiome from leucine.	IVA has been linked to improve glucose sensitivity and may effect adipocyte lipid metabolism. A metabolic product of the breakdown of leucine, IVA is metabolised further with isovaleryl-CoA dehydrogenase to energy-producing compounds, or secondary metabolites that can be excreted. Lack of the dehydrogenase results in IVA buildup and isovaleric acidemia.
Caproate	1	Raoultella ornithinolytica;	37	Observed in cheeses and vanilla, and along with caprate and caprylate, constitutes 15% of the fats in goat's milk. A fecal biomarker for the overgrowth of Clostridioides difficile.	Readily absorbed; transported to, and metabolised by, the liver. Not incorporated in chylomicrons; is transported as the free acid in the bloodstream (Schonfeld2016).
Heptanoate	0		28	Human breast milk, apples, clove, ginger, black tea, grapes, scallops, leek and processed foodstuffs such as jams, soups and sauces. Esters of heptanoate can be found in tabasco peppers and blackberries.	Readily absorbed; transported to, and metabolised by, the liver. Not incorporated in chylomicrons; is transported as the free acid in the bloodstream (Schonfeld2016).
Caprylate	0		43	Human breast milk and goat's milk; a minor constituent of coconut, babassu and palm kernel oils.	Readily absorbed; transported to, and metabolised by, the liver. Not incorporated in chylomicrons; is transported as the free acid in the bloodstream (Schonfeld2016). Readily degraded and has a low tendency to be stored as a triglyceride. Reported to improve intestinal barrier function in mouse models. Serum concentrations decline in patients with chronic kidney disease (Toyohara2010).
Nonanoate	0		18	Human breast milk; esters of nananonate found in milk, rice, beans, apples, bananas, blackberries, butter, cheese, grapes, hop oil, pineapples, strawberries, vanilla and white wine.	Readily absorbed; transported to, and metabolised by, the liver. Not incorporated in chylomicrons; is transported as the free acid in the bloodstream (Schonfeld2016).
Caprate	2	Bacteroides ovatus; Serratia marcescens;	70	Human breast milk, butter, goat's milk and coconut oil.	Readily absorbed; transported to, and metabolised by, the liver. Not incorporated in chylomicrons; is transported as the free acid in the bloodstream (Schonfeld2016).