What Are Fermentable Carbohydrates?

Fermentable carbohydrates are the sugars that are easily fermented in your digestive system, which include oligosaccharides, disaccharides, monosaccharides and polyols. They are composed of short chains of sugar molecules, making them easy to break down. Once these sugars reach your large intestine, bacteria rapidly ferment them. This can contribute to gastrointestinal symptoms in sensitive individuals with GI problems, such as irritable bowel syndrome, or IBS. A low fermentable carbohydrate diet is designed to relieve gastrointestinal symptoms.

Fermentable carbohydrates aren't necessarily bad guys. They serve as food for the colonies of friendly bacteria living in your intestines. However, some individuals are sensitive to the action of fermentation, which is the process of bacteria feeding on these carbohydrates and converting them to other substances, such as gas. This draws water and gas into the bowel, which can cause bloating, burping, flatulence, abdominal cramps, and diarrhea or constipation. These symptoms can become bothersome if you're particularly sensitive.

Fructose, or fruit sugar, is a fermentable carbohydrate found in vegetables, fruit and honey. Lactose, or milk sugar, is another fermentable carbohydrate. It's found in milk and products made with milk. Fructans, found in breads, cereals and pasta, and galactans, found in beans and other legumes, also belong to the fermentable carbohydrate group. The final class of fermentable carbohydrates are polyols, also known as sugar alcohols. These are found in certain fruits, such as apples, pears, nectarines, peaches, plums, apricots and cherries.

Although fermentable carbohydrates are not the cause of IBS, they may trigger symptoms if you have the condition. Researchers found that a diet low in fermentable carbohydrates significantly improves gastrointestinal symptoms, according to a study published in the September 2013 issue of the "International Journal of Clinical Practice." The study followed 90 patients for more than a year. About 75 percent of the patients adhered to a low fermentable carbohydrate diet and experienced improvement in bloating, abdominal pain, flatulence and diarrhea.

The "International Journal of Clinical Practice" study concluded that a low- fermentable-carbohydrate diet is effective for treating gastrointestinal disorders such as irritable bowel syndrome. This diet excludes foods high in fermentable carbohydrates. For example, apples, pears and mangoes are high in fructose, while bananas, blueberries and grapefruit have a low fructose content. Following a low-fermentable-carbohydrate diet requires nutritional coaching from a dietitian trained in this particular diet. Talk to your dietitian to find out whether this diet is the right approach for you.