What are short-chain fatty acids ?

Short-chain fatty acids (SCFA) contain 2-5 carbon (C) atoms. They are mainly produced during fermentation of the soluble dietary fiber by beneficial large intestinal bacteria. They include :

短鏈脂肪酸（SCFA）含有2-5個碳原子。它們主要通過有益的大腸細菌在可溶性膳食纖維的發酵過程中產生。他們包括 ：


Acetic acid (2 C atoms) 乙酸，也叫醋酸、冰醋酸
Propionic acid (3 C atoms)丙酸，又稱初油酸，是三個碳的羧酸和短鏈飽和脂肪酸。
Butyric acid (4 C atoms)丁酸，又稱酪酸，存在於腐臭的黃油、帕馬森乾酪、嘔吐物和腋臭中。
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乙酸 醋酸菌，它是一種喜氧細菌。
丙酸 初油酸桿菌，它是一種厭氧細菌。
丁酸是脂肪酸，在動物脂肪和植物油中以丁酸酯形式存在。
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SCFA Functions
SCFA are considered the main nutrients for the large intestinal lining cells; they also increase the blood flow, muscle activity and water absorption in the colon . SCFA are partly used as food for beneficial bacteria and partly they are absorbed and metabolized – this is why soluble dietary fiber, from which colonic bacteria produce SCFA, has 1-3.8 Calories per gram .

SCFA功能
SCFA被認為是大腸內膜細胞的主要營養元素 ；它們還增加了結腸中的血流量，肌肉活動和結腸吸水率。 SCFA部分用作有益細菌的食物，部分被吸收和代謝 - 這就是為什麼結腸細菌產生SCFA的可溶性膳食纖維具有每克1-3.8卡路里的原因。


SCFA Food Sources
The following soluble dietary fiber produces most SCFA in the large intestine :

SCFA食物來源
以下可溶性膳食纖維在大腸中產生大多數SCFA：

Resistant starches from whole-grain cereals, barley, brown rice, beans, lentils, green bananas, cooked and cooled potatoes or pasta
抗性澱粉 全麥穀物，大麥，糙米，豆類，扁豆，綠色香蕉，熟和冷馬鈴薯或麵食的抗性澱粉

Pectin from apples, apricots, blackberries, carrots and oranges
果膠 蘋果，杏，黑莓，胡蘿蔔和橙子的果膠
Fructooligosaccharides (FOS) and inulin from Jerusalem artichokes, onions, leeks, wheat, rye and asparagus
果寡糖 來自菊芋，洋蔥，韭蔥，小麥，黑麥和蘆筍的低聚果糖（FOS）和菊粉


Arabinoxylan 阿拉伯木聚醣
Guar gum 關華豆膠（Guar gum），也叫做 瓜爾膠（guaran），是一種半乳甘露聚醣（galactomannan）。
Butyrate in Dairy 帕馬森起司

Butter, certain cheeses and cow’s milk contain considerable amounts of butyric acid in the form of butyrate (a compound of butyric acid and glycerol) [4]; note that these foods are also high in saturated fats.

In rancid butter, butyric acid appears in the free form–not bound to glycerol as in normal butter–and causes unpleasant odor.

SCFA (Butyrate) Supplements
Short-chain fatty acid supplements, mostly butyric acid salts, such as sodium, potassium, calcium and magnesium butyrate, are available without prescription (over-the-counter).

Butyrate supplements are–like other fatty acids–absorbed in the small intestine, so they cannot promote the growth of beneficial colonic bacteria or clean the large intestine (colon), as advertised. There is no scientific evidence about their effectiveness as liver or biliary tree cleansers, or ammonia or neurotoxin detoxifiers.

Possible Short-Chain Fatty Acids (SCFA) Benefits

Adding resistant starches (which generate SCFA in the colon) to oral rehydration solution (ORS) may help to reduce acute diarrhea in small children [5], including diarrhea in cholera [1]. Cooked green bananas (high in resistant starches) or pectin (which is a soluble fiber), which both generate SCFA in the colon, may help to relieve chronic diarrhea in children [6].
When feeding by mouth is not possible for certain periods of time, like after a gastrointestinal surgery, colonic lining may undergo a rapid degradation (atrophy). Short-chain fatty acids (SCFA) used in intravenous infusion help to nourish colonic lining and thus prevent its degradation [7].
There is INSUFFICIENT EVIDENCE about the effectiveness of short-chain fatty acids (SCFA) in the prevention or treatment of colorectal cancer [2,8,9], ischemic stroke, treating obesity, high blood cholesterol, diabetes type 2, sickle cell disease, Crohn’s disease and ulcerative colitis [10,11,12,13], post-infectious irritable bowel syndrome (IBS) [7], increasing calorie delivery in cystic fibrosis [14], prevention ammonia or toxins absorption from the intestine, constipation, antibiotic-associated diarrhea.

The role of SCFA produced by the intestinal bacteria in immunity is not clear yet: they may either promote or inhibit inflammation in the body [17,18,19].

Ethyl Butyrate, Methyl Butyrate, Propionate

Ethyl butyrate and methyl butyrate are esters of butyric acid and ethanol or methanol. They have a fruity odor, so they can be used as food flavors added to orange juice, other fruit products or alcohol beverages, such as martini. Butyric acid is industrially produced by fermentation of starch by the bacterium Bacillus subtilis.

Propionic acid is also produced by bacteria from the genus Propionibacterium and is responsible for a specific flavor of Swiss cheese [15]. Propionic acid (E-number = E280) and its salts sodium propionate (E281), calcium propionate (E282) and potassium propionate (E283) can be used as food preservatives or flavorings; they are Generally Recognized As Safe (GRAS) by the U.S. Food and Drug Administration (FDA) [16].

Another short-chain fatty acid that is different than above ones is alpha-lipoic acid.


短鏈脂肪酸