Short-chain fatty acids

Short-chain fatty acids are produced by the "friendly" bacteria in your gut. These fatty acids are the primary source of nutrients for the cells of the intestine. Short-chain fatty acids also play an important role in health and disease prevention. They may reduce the risk of inflammatory diseases, type 2 diabetes and other diseases (1). This article will take a closer look at how short-chain fatty acids affect health.

What are short-chain fatty acids?

Short-chain fatty acids are fatty acids with less than 6 carbon atoms (2). They are produced when the "healthy" gut bacteria ferment fiber in the intestine and these fatty acids are the primary source of energy for the cells of the inner intestinal wall. For this reason, short-chain fatty acids play an important role in gut health (1). Excess amounts of these fatty acids are used for other functions in the body. For example, they can cover roughly 10% of your daily calorie requirements (2). Short-chain fatty acids are also involved in the metabolism of important nutrients such as carbohydrates and fat (3). Around 95% of the short-chain fatty acids in your body are in the form of the following fatty acids:

Acetate (2 carbon atoms).
Propionate (3 carbon atoms).
Butyrate (4 carbon atoms).

Propionate is mainly involved in the production of glucose in the liver, while acetate and butyrate are incorporated into other fatty acids and cholesterol (4).

There are many factors that influence the amounts of short-chain fatty acids in your gut. These include the number of microorganisms present, the food sources consumed and the time it takes for the food to be transported through the digestive tract (5).

Summary: Short-chain fatty acids are produced when fiber is fermented in the gut. They act as an energy source for the cells of the inner intestinal wall.

Food sources of short-chain fatty acids

Eating a lot of fiber-rich foods such as fruits, vegetables and legumes is associated with increased production of short-chain fatty acids (6). A study of 153 subjects found a positive relationship between a higher intake of plant foods and increased levels of short-chain fatty acids in the stool (7). The amount and type of fiber you eat affects the composition of bacteria in your gut, which in turn affects which short-chain fatty acids are produced (8). For example, studies have shown that consuming more fiber increases butyrate production, while reducing fiber intake reduces production (9).

The following types of fiber are best for the production of short-chain fatty acids in the gut (10, 11):

Inulin: You can consume inulin through artichokes, garlic, leeks, onions, wheat, rye and asparagus.
Fructooligosaccharides (FOS): FOS are found in various fruits and vegetables, which include bananas, onions, garlic and asparagus.
Resistant starch: You can get resistant starch from cereals, barley, rice, beans, green bananas, pulses and potatoes that have been cooked and then cooled down
Pectin: Good sources of pectin are apples, apricots, carrots and oranges.
Arabinoxylan: Arabinoxylan is found in cereal grains. For example, it is the most common fiber in wheat bran and accounts for about 70% of the total fiber content.
Guar gum: Guar gum can be obtained from guar beans, which belong to the legume family.

Some types of cheese, butter and cow's milk also contain small amounts of butyrate. Summary: Fiber-rich foods such as fruit, vegetables, legumes and whole grains stimulate the production of short-chain fatty acids.

Short-chain fatty acids and digestive disorders

Short-chain fatty acids can be helpful for some digestive disorders. Butyrate, for example, has anti-inflammatory effects in the intestine (12).

Diarrhea

Your gut bacteria convert resistant starch and pectin into short-chain fatty acids and eating this fiber has been shown to reduce diarrhea in children (13, 14).

Inflammatory bowel diseases

Ulcerative colitis and Crohn's disease are two of the main types of inflammatory bowel disease. Both are characterized by chronic intestinal inflammation. Due to its anti-inflammatory properties, butyrate has been used to treat both conditions. Studies with mice have shown that butyrate supplements reduced intestinal inflammation and acetate supplements have similar effects. In addition, lower levels of short-chain fatty acids have been associated with an exacerbation of ulcerative colitis (15, 16). Human studies also suggest that short-chain fatty acids - and butyrate in particular - may reduce symptoms of ulcerative colitis and Crohn's disease (17, 18, 19, 20). A study of 22 patients with ulcerative colitis found that consuming 60 grams of oat bran per day over a 3-month period improved symptoms (17). Another small study found that butyrate supplements resulted in clinical improvements and remission in 53% of Crohn's disease patients (18). For ulcerative colitis patients, a short-chain fatty acid enema twice a day for 6 weeks helped reduce symptoms by 13% (21).

Summary: Short-chain fatty acids may reduce diarrhea and help treat inflammatory bowel disease.

Short-chain fatty acids and bowel cancer

Short-chain fatty acids may play a key role in the prevention and treatment of certain cancers, primarily colorectal cancer (22, 23, 24). Laboratory studies show that butyrate helps to keep the cells of the intestine healthy by preventing the growth of tumor cells and stimulating the destruction of cancer cells in the intestine (24, 25, 26, 27). However, the mechanisms underlying these effects are still unclear (28, 29, 30). Several observational studies suggest a link between high-fiber diets and a reduced risk of colorectal cancer. Many experts suspect that the production of short-chain fatty acids could be partly responsible for this (28, 30). Some studies conducted with animals also report a positive link between a high-fiber diet and a reduced risk of colorectal cancer (31, 32). In one study, mice fed a high-fiber diet and whose intestines contained butyrate-producing bacteria had 75% fewer tumors than mice that did not have these bacteria (33). Interestingly, the high-fiber diet alone - without the butyrate-producing bacteria - had no protective effect against colorectal cancer. A low-fiber diet was also ineffective, even with butyrate-producing bacteria (33). This suggests that the anti-cancer benefits only exist when a high-fiber diet is combined with the right bacteria in the gut. However, human studies have yielded mixed results. Some suggest a link between a high-fiber diet and reduced cancer risk, while others have found no association (34, 35, 36, 37). However, these studies did not look at gut bacteria and individual differences in gut bacteria may play a role.

Summary: Short-chain fatty acids have been shown to protect against cancer in laboratory and animal studies. However, further studies are needed in this regard.

Short-chain fatty acids and diabetes

One study review reported that butyrate may have beneficial effects in humans and animals with type 2 diabetes (38). The same review also highlighted that there appears to be an imbalance of microorganisms in the gut of people with diabetes (38, 39). Short-chain fatty acids have been shown to increase enzyme activity in the liver and muscle tissue, resulting in better blood glucose control (40, 41, 42). In animal studies, acetate and propionate supplements improved blood glucose levels in diabetic mice and healthy rats (43, 44, 45). However, few studies have been conducted in humans and the results are mixed. One study found that propionate supplements reduced blood sugar levels, but another study found that short-chain fatty acids in the form of supplements did not significantly affect blood sugar control in healthy humans (46, 47). A number of human studies have also reported associations between fermentable fiber and improved glycemic control and insulin sensitivity (48, 49). However, this effect can generally only be observed in individuals who are overweight or insulin resistant and not in healthy people (46, 47, 50)

Summary: Short-chain fatty acids appear to help regulate blood glucose levels, which is particularly the case in people suffering from diabetes or insulin resistance.

Short-chain fatty acids and weight loss

The composition of the microbiota in the gut can influence nutrient absorption and energy regulation and thereby also the development of obesity (51, 52). Studies have shown that short-chain fatty acids can also regulate fat metabolism by increasing fat burning and reducing fat storage (8). When this happens, the amount of free fatty acids in the blood is reduced and this could also help protect against weight gain (40, 53, 54, 55). Several animal studies have investigated this effect. After five weeks of treatment with butyrate, obese mice lost 10.2% of their original body weight and body fat percentage decreased by 10%. In rats, acetate supplements reduced fat storage (40, 56). However, the evidence linking short-chain fatty acids to weight loss is mainly based on animal and test tube studies. Summary: Animal and test tube studies suggest that short-chain fatty acids may help reduce obesity. However, further human studies are needed.

Short-chain fatty acids and heart health

Many observational studies have linked high-fiber diets with a reduced risk of heart disease. However, the strength of this association is often related to the type and source of fiber (57). In humans, fiber intake has also been associated with reduced inflammation (58). One of the reasons that fiber reduces the risk of heart attack may be based on the production of short-chain fatty acids in the gut (59, 60, 61). Both animal and human studies have reported that short-chain fatty acids can lower cholesterol levels (28, 62, 63, 64, 65). Butyrate is believed to interact with key genes responsible for cholesterol production, which could potentially lower cholesterol production (66). For example, cholesterol production decreased in the livers of rats given propionate supplements. Acetate acid also reduced cholesterol levels in rats (62, 67, 68). The same effect was also observed in humans, as the acetate contained in vinegar reduced the amount of excess cholesterol in the bloodstream (64).

Summary: Short-chain fatty acids may reduce the risk of heart disease by reducing inflammation and blocking cholesterol production.

Should you use a supplement?

Supplements that provide short-chain fatty acids usually contain butylic acid salts. These are generally referred to as sodium, calcium, potassium or magnesium butyrate. However, supplements may not be the best way to increase short-chain fatty acid levels. Butyrate supplements are absorbed before they reach the colon, which means that all the benefits for the intestinal cells are lost. In addition to this, there is very little evidence on the effectiveness of short chain fatty acids in supplement form.

Butyrate reaches the gut best when it is produced by fermentation of dietary fiber. For this reason, increasing your intake of high-fiber foods is probably a much better way to increase your levels of short-chain fatty acids.

Summary: Eating high-fiber foods is the best way to increase short-chain fatty acid levels as supplements are absorbed before they reach the gut.

Conclusion

Due to their anti-inflammatory and anti-cancer effects, it is likely that short-chain fatty acids have a wide range of beneficial effects on the body. One thing is for sure: taking care of the friendly bacteria in your gut can lead to a wide variety of health benefits. The best way to nourish your good gut bacteria is to eat plenty of foods rich in fermentable fiber.