What Are Common Dietary Fermentable Carbohydrates?

Patient Presentation
A 2-month-old female came to clinic for her well child examination. She was a term infant and the parents complained that she was “gassy.” They said she would cry briefly around the time she had a bowel movement and would turn very red. They also would hear bowel sounds occasionally around the time she was breastfeeding or stooling. The stool had a soft, toothpaste-like quality and she had 1-2 stools/day without blood or mucous. The family was using simethicone drops to help with the “gas.” The parents said that the baby herself didn’t seem distressed but it worried them.

The pertinent physical exam showed a smiley infant with growth parameters around the 75%. Her examination was normal. The diagnosis of a healthy baby was made. The pediatrician explained the natural history of how infants’ stools changed from birth over time, as well as normal bowel movement patterns. “It’s not uncommon for babies’ faces to turn red as they are stooling or to make sounds. Remember for babies they often don’t have gravity to help them to pass stools and also aren’t as active as older children and adults. When we are passing stools it also isn’t uncommon for us to make sounds, plus we aren’t being watched. Our faces probably change color if we looked in a mirror,” she pointed out. “What you can do if she seems to be having a problem is to bicycle her legs and the movement may help the gut to move the stool along. Also gently rubbing the abdomen may also help. Remember don’t push, just gently rub. The simethicone probably isn’t doing much but shouldn’t hurt her,” she commented.

Parents may often come to the pediatrician for concerns about crying and colic, increased belching, abdominal distention, increased flatulence, abdominal pain or stool changes. They complain of increased “gassiness,” which could mean any or a combination of these problems, or something different that they believe is referred to the abdomen. In newborns parents’ intolerance for crying and normal changes in the abdomen (e.g. appearing larger or smaller) may have them complain of “gassiness” but they do not mean actual belching or flatulence. In older children, parents may state that the child has abdominal pain and again is “gassy,” and may or may not mean increased belching or flatulence. Of course other common problems such as constipation or infectious diarrhea need to be considered and teased out when parents bring their children for these complaints.

Gases within the intestinal tract are normal. They are a combination of swallowed air and fermentation processes within the tract. Fermentation is usually thought of as sugar digestion but fat and protein can also produce gases. Through these processes a variety of substrates are created and can be used by the body. Gases include hydrogen, oxygen, nitrogen, carbon dioxide, methane and the rotten egg smell to flatulence is due to hydrogen sulfide.

Learning Point
Dietary carbohydrates can be a culprit in “gassiness” and other abdominal complaints. Malabsorbed carbohydrates are osmotically active and are quickly fermented by colonic bacteria. They can cause rapid increase in luminal distention leading to abdominal symptoms such as increased gas, bloating, pain and/or loose or more frequent stools or frank diarrhea. Specifically this occurs by increasing the fermentable substrate which then increases gas production leading to luminal distention, and by increasing the luminal osmotic load which increases the luminal fluid leading to luminal distention. There are a variety of factors which may promulgate or mitigate symptoms including amount of carbohydrate ingested, ingestion with other substances (i.e. eating a meal or the substance individually), gastric emptying rate, transit time of the small intestine, concomitantly ingested bacteria able to break down the carbohydrate, “colonic bacteria adaption to one’s diet,” and other host factors.

Common dietary fermentable carbohydrates include:

  • Glucose, a monosaccharide, found in honey, fruits, some vegetables (e.g. sweet corn)
  • Maltose, a disaccharide of glucose and glucose, found in barley, wheat, cornmeal and fruits (e.g. pears, peaches)
  • Starch, polymers of glucose, found in staple foods such as potatoes, corn, wheat and also fruits
  • Fructose, a monosaccharide, found in honey and fruits (e.g. pears, apples)
  • Lactose, a disaccharide of glucose and galactose, found in dairy products
  • Sucrose, a disaccharide of glucose and fructose, found in sugar cane, sugar beets, and other fruits and vegetables
  • Fructans, fructose polymers, found in wheat, rye and onions
  • Galactans, galactose polymers, found in legumes and beans
  • Polyols, sugar alcohols, found in fruits (e.g. cheeries, pears, and apricots) and sweetener substitutes (e.g. sorbitol, xylitol)

Glucose, maltose, starch and sucrose are usually easily digested by small intestine enzymes and absorbed, but enzyme deficiencies can cause problems. Lactose is a unique disaccaride as it is only found in mammalian milk. Lactase the enzyme that breaks it down into glucose and galactose is found in the small intestinal villi tips and its highest concentration is found in infants. The lactase concentration decreases with age and only about 30% of the population has persistence into adulthood and this persistence is mainly in people of northern European descent. Glucose and galactose are absorbed by the small intestine. Fructose uses the glucose transporter in the small intestine for absorption. Fructans, galactans and polyols are complex carbohydrates which enter the colon intact and are metabolized by gut bacteria.

Dietary fiber is commonly used in older children as an intervention to help with abdominal complaints. Dietary fiber are plant components which cannot be completely broken down by the body. They are found in whole grains, cereals, legumes, fruits, vegetables and nuts. They can be soluble or insoluble. Soluble fiber maintains the stool hydration by absorbing water and provides bulk to the stool. Psyllium is a common soluble fiber. Insoluble fiber mechanically stimulates the gut mucosa to secrete mucous and water and decrease the colonic transit time.

Probiotics theoretically work by colonizing the bowel, secreting antibacterial substances, competing with other organisms for nutrients and preventing adhesion to the intestinal epithelium and regulation of the immune system. The data on effectiveness can sometimes be conflicting. Two other potential interventions marketed to parents of infants are simethicone and gripe water. Simethicone is an antifoaming agent that purportedly works by creating larger gas bubbles that are more easily passed through the digestive system. Gripe water may have a variety of components including sodium bicarbonate acting as an antacid, ginger, fennel and possible other components. Ginger and fennel have some studies which support their use as digestive aids.

Questions for Further Discussion
1. What parent advice to you recommend for infant crying and/or colic? A review can be found here
2. What is in the differential diagnosis of acute abdominal pain? A review can be found here
3. What is in the differential diagnosis of recurrent abdominal pain? A review can be found here
4. What is irritable bowel syndrome? A review can be found here

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Gas

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Skinmore-Roth L. Mosby’s Handbook of Herbs & Natural Supplements. 4th ed.St. Lois, MO: Mosby/Elsevier; 2010.

Chumpitazi BP, Shulman RJ. Dietary Carbohydrates and Childhood Functional Abdominal Pain. Ann Nutr Metab. 2016;68(Suppl. 1):7-17. doi:10.1159/000445390

Chumpitazi BP, Weidler EM, Shulman RJ. Lactulose Breath Test Gas Production in Childhood IBS Is Associated With Intestinal Transit and Bowel Movement Frequency. Journal of Pediatric Gastroenterology & Nutrition. 2017;64(4):541-545. doi:10.1097/MPG.0000000000001295

Williams BA, Grant LJ, Gidley MJ, Mikkelsen D. Gut Fermentation of Dietary Fibres: Physico-Chemistry of Plant Cell Walls and Implications for Health. International Journal of Molecular Sciences. 2017;18(10). doi:10.3390/ijms18102203

Simethicone. MedLinePlus. https://medlineplus.gov/druginfo/meds/a682683.html Last revised 2/15/18.

Probiotics: What You Need To Know. National Center for Complimentary and Integrative Health. https://www.nccih.nih.gov/health/probiotics-what-you-need-to-know. Last revised 8/2019.

Ouald Chaib A, Levy EI, Ouald Chaib M, Vandenplas Y. The influence of the gastrointestinal microbiome on infant colic. Expert Rev Gastroenterol Hepatol. 2020 Oct;14(10):919-932. doi: 10.1080/17474124.2020.1791702. Epub 2020 Jul 21.

Ginger. National Center for Complimentary and Integrative Health. https://www.nccih.nih.gov/health/ginger. Last revised 12/2020

Pi X, Hua H, Wu Q, Wang X, Wang X, Li J. Effects of Different Feeding Methods on the Structure, Metabolism, and Gas Production of Infant and Toddler Intestinal Flora and Their Mechanisms. Nutrients. 2022;14(8):1568. doi:10.3390/nu14081568