Butyric Acid, Gut Bacteria, and Colon Health
An Important Chemical for Health
Our large intestine hosts a huge population of bacteria that have many effects on our lives. Most of these effects are believed to be beneficial. Some of our intestinal bacteria convert the soluble fiber and resistant starch present in undigested food into short-chain fatty acids. One of these fatty acids is butyric acid, which has health benefits in the large intestine. It helps to maintain a healthy intestinal lining and may reduce symptoms of inflammatory bowel disease. It may also lower the risk of colon cancer, though this benefit is less certain.
The colon is the longest section of the large intestine and houses the greatest number of gut bacteria. The amount of butyric acid formed in the colon depends on which bacteria live there and on how much soluble fiber and resistant starch is present. It’s also determined by the size of the bacterial population that is able to produce the butyric acid and by how long the fiber or starch stays in the colon. The study of gut bacteria and their needs and effects is very important. Keeping the bacteria healthy could also help to keep us healthy.
The Digestive or Gastrointestinal Tract
The Digestive Tract, Digestion, and Gut Bacteria
When food is swallowed, it passes through a tube called the digestive or gastrointestinal tract. The tube starts at the mouth and ends at the anus. The food is gradually digested as it travels. Digestion is the process in which food is broken down into small particles that can be absorbed.
The food that we eat gives us nutrition, but it also feeds the bacteria in our intestine. Most of these bacteria live in the colon. The small intestine and the rectum also contain bacteria, however. The concept of feeding both ourselves and our helpful gut bacteria is gradually becoming more popular. "Gut" is another word for the digestive tract or the intestine.
The general processes that occur in the digestive tract are as follows.
- Food is digested in the mouth, stomach, and small intestine.
- The products of digestion are absorbed through the lining of the small intestine into the bloodstream.
- The blood carries the nutrients to where they're needed.
- The indigestible food passes from the small intestine into the large intestine.
- Bacteria in the large intestine act on the food residue, producing a variety of chemicals.
- The lining of the large intestine absorbs water, salts, and vitamins.
- The remaining food residue is released from the large intestine through the anus as feces (or stool).
Studying Gut Bacteria in the Intestinal Microbiome
The Large Intestine and the Colon
The bacterial community in the colon is often referred to as the intestinal microbiome. Researchers are discovering that colon bacteria are very active. Many of them are beneficial. Some appear to be neutral and a few are harmful. In a healthy gut, the effects of the helpful bacteria overshadow the effects of the harmful ones. The study of gut bacteria is exciting because the bacteria may have profound effects on our lives and health.
The large intestine is made of the ascending colon, the transverse colon, the descending colon, and the rectum. Most of the bacteria live in the three sections of the colon, which are collectively known as simply "the colon".
What Is Soluble Fiber?
The human body can’t digest soluble fiber. This doesn't mean that the fiber is useless, however. In fact, it has health benefits. It dissolves in the water present in the digestive tract, forming a gel. This gel lowers the level of LDL cholesterol (the so-called “bad” cholesterol) in the blood. It also lowers the blood sugar level. Another health benefit of soluble fiber is that it can be fermented by certain colon bacteria to produce butyric acid.
Good sources of soluble fiber include barley, oatmeal, beans, peas, carrots, apples, pears (not including the peel), and many other types of fruits and vegetables. The peels of fruits and vegetables contain insoluble fiber. The body can't digest this material. Like soluble fiber, however, it has benefits, including bulking up the stool and relieving constipation.
Substances that cause butyric acid to be made by gut bacteria are said to be butyrogenic. The bacteria that make the butyric acid are also said to be butyrogenic.
Soluble and Insoluble Fiber
What Is Resistant Starch?
Resistant starch is starch that we are unable to digest or that we digest very slowly. The amount of resistant starch in a food depends not only on the identity of the food but also on factors such as whether the food is cooked or raw, whether it's cooked and then cooled (which changes the nature of the starch), and its degree of ripeness. Some good sources of resistant starch are cooked potatoes that have been chilled, rice, pasta, unripe bananas, legumes such as navy beans and lentils, and high-amylose corn.
The glycemic index is a number that represents the ability of a food to raise the level of glucose in the blood. Glucose is the technical name for blood sugar. In general, food with a high glycemic index is considered to be bad, since it may lead to an increase in body fat and a higher risk of diabetes and heart attacks.
Resistant starch has little effect on blood sugar level and is therefore classified as a low glycemic substance. The glycemic index of a food containing resistant starch depends on the proportion of resistant starch to higher glycemic carbohydrates in the food. Some colon bacteria can ferment resistant starch to make butyric acid, which is another benefit of the substance.
What Is Butyric Acid?
A fat molecule is composed of a glycerol molecule joined to three fatty acid molecules. The whole structure is sometimes known as a triglyceride. Butyric acid, also called butanoic acid, is a fatty acid present in some triglycerides. It's released when the fat is broken down.
Some articles about butyric acid refer to butyrate. Butyric acid and the butyrate ion have slightly different structures, although they are very similar. The final hydrogen atom shown in the formula above has been lost in a butyrate ion, which is also called a butanoate ion. The ion can form substances called butyrate salts.
Butyric acid is a short-chain fatty acid, or SCFA, as opposed to a medium-chain or long-chain fatty acid. SCFAs have an acid group (COOH) at one end of their molecule and a “tail” or chain containing fewer than six carbon atoms attached to the acid group.
Some foods contain relatively high concentrations of butyric acid, including butter and parmesan cheese. Butyric acid reportedly makes up 3% to 4% of butter. Kombucha tea also contains the acid. The kombucha culture is a mixture of bacteria and yeasts. If the culture is placed in tea that has been sweetened with sugar and the microbes are allowed to ferment the sugar, a variety of chemicals are produced, including butyric acid.
A Smelly Chemical
Butyric acid has a very unpleasant odor and smells like vomit. In fact, the chemical is present in vomit. When butter becomes rancid, enzymes produced by bacteria release the butyric acid from the fat molecules, producing the typical rancid smell. The acid got its name from “butyrum”, the Latin word for butter, which in turn was based on a similar Greek word.
Concentrated butyric acid must be handled very carefully, not only because of its nauseating smell but also because it’s corrosive. At low concentrations, however, the acid is safe. In very low concentrations, it’s used as a flavoring agent in food.
Potential Health Benefits of Butyric Acid
Butyric acid is a saturated fatty acid. Saturated fats contain saturated fatty acids and have a reputation for creating health problems if eaten in excess. These problems include increasing the amount of LDL cholesterol in the blood. A high cholesterol level may lead to fatty plaque deposits in arteries and increase the risk of a heart attack or a stroke. Excess cholesterol may also increase the risk of some types of cancer. Researchers are discovering that not all saturated fats produce these effects, however. Butyric acid and other short-chain fatty acids actually have health benefits.
Butyric acid is the main food source of the colonocytes, which are cells in the lining of the colon. The chemical supports the colonocytes, helping them to function properly and maintaining the integrity of the intestinal lining.
Butyric acid may help people suffering from Crohn’s disease and ulcerative colitis. These disorders are classified as inflammatory bowel diseases, or IBD. Butyric acid enemas have reduced colon inflammation symptoms in some IBD patients. Further exploration of this effect is needed, however.
Probiotics are living bacteria or yeasts that provide health benefits when ingested. One problem faced by probiotic companies is that the microbes that they provide must not only survive their journey through the digestive tract but also stay in the intestine long enough to be beneficial.
Butyric Acid Enemas and Probiotics
Butyric acid enemas are sometimes offered to people with IBD. Unfortunately, the enemas smell bad and patients are not always willing to undergo the treatment. Another problem with an enema is that the butyric acid doesn’t stay in the colon for very long.
Researchers are investigating the use of probiotic supplements containing bacteria that can make butyric acid. If the probiotic bacteria multiply in the colon and become permanent inhabitants, the patient will have a continuous supply of a potentially useful chemical. A probiotic supplement should be much more pleasant to take than an enema.
Butyric Acid and Colon Cancer
Apoptosis—programmed cell death—is a normal process in cells. For example, cells may be stimulated to undergo self-destruction if their DNA is damaged so severely that it can’t be repaired or if there are too many cells in an area. Cancer cells do not undergo apoptosis and continue to multiply, however.
In some experiments with lab animals, butyric acid has been found to inhibit multiplication of cancerous colonocytes and stimulate apoptosis in the cells. Not all experiments concerning butyric acid and cancer have shown benefits, however. Nevertheless, the preliminary research results are intriguing.
The study of butyric acid or butyrate in relation to cancer is difficult. The surrounding environment seems to be very important in determining the effect of the chemical in the intestine. More research is needed before scientists agree that butyric acid can prevent or treat colon cancer in humans.
Anyone who wants to use butyric acid in larger amounts than found in food should consult a doctor. Substances used as medications often have side effects as well as benefits. The side effects are sometimes serious.
Increasing the Amount of Butyric Acid in the Colon
One plan for someone hoping to increase the amount of butyric acid in their colon is to eat foods that are high in soluble fiber and resistant starch. These substances should act as nutrients for appropriate gut bacteria. Since butter and parmesan cheese contain butyric acid, they could be used to support gut health as well. However, these foods also contains longer chained saturated fats, some of which may be unhealthy.
The recommendation from the majority of nutritionists and health agencies is to limit the amount of saturated fat in our diet. The suggestions for fat consumption in the American Heart Association article mentioned below are standard ones. The association says that research over many years has shown that saturated fats are bad for the cardiovascular system.
In the last few years, however, some dissenting opinions about saturated fats have arisen. Some researchers disagree with the idea that they are bad for the circulatory system and say that their demonization is wrong. Hopefully the situation will be clarified soon. The type of fat that we eat is an important topic for those of us that are concerned about our health.
The Importance of Supporting Gut Bacteria
Maintaining a helpful intestinal microbiome is very important. Scientists are learning more about the functions of bacteria in the colon and about how to add new ones to the intestinal population. It may one day be possible for us to eat or drink probiotic supplements that supply us with bacteria that will prevent or treat specific health problems. Until then, it seems like a good idea to support our present gut bacteria so that they can make substances that may provide significant health benefits, including butyric acid.
- Załęski A, Banaszkiewicz A, Walkowiak J. Butyric acid in irritable bowel syndrome. Przegla̜d Gastroenterologiczny. 2013;8(6):350-353. doi:10.5114/pg.2013.39917 (Includes a reference relating to the effect of butyric acid on intestinal inflammation in humans)
- Butyric acid and intestinal inflammation in mice from nature.com (Also includes references relating to the treatment of IBD in humans with butyric acid)
- Butyrate and colorectal cancer from the NIH (National Institutes of Health)
- American Heart Association recommendations for saturated fat intake
Questions & Answers
© 2011 Linda Crampton