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clinical background

Gut Reaction #28: Carbohydrates, maldigestion and malabsorption

Carbohydrates are commonly consumed as part of a typical Western diet. This blog will highlight some of the problems that carbohydrates may pose if there are problems with digestion or absorption.

Carbohydrate digestion starts in the upper part of the small intestine where enzymes (e.g. lactase) break down the larger carbohydrates (polysaccharides or starches) into smaller monosaccharides which are absorbed into the blood stream. If this process is incomplete (maldigestion or malabsorption) excess carbohydrates may reach the colon where fermentation by bacteria can lead to the production of excess gas (hydrogen, carbon dioxide and methane) and fatty acids (butyrate and propionate) leading to abdominal cramps, flatulence, bloating and diarrhoea.

Symptoms related to carbohydrate malabsorption or maldigestion may occur in patients with irritable bowel syndrome, small intestine bacterial overgrowth, coeliac or Crohn’s disease or after surgery or radiotherapy to the gut. In addition, some people may have a relative lack of enzymes, such as lactase or fructase, leading to an inability to breakdown and absorb lactose- or fructose-containing foods such as dairy products or fruits.

Carbohydrate malabsorption or maldigestion may be suspected during consultation with a gastroenterologist or dietician. Hydrogen breath tests may be undertaken to confirm lactose intolerance or fructose intolerance. If confirmed, symptoms may be helped by reducing lactose or fructose containing food items. A lactulose hydrogen breath test may be performed to look for SIBO and if abnormal, individuals may respond to dietary changes, an antibiotic or probiotic.

The link between ingested carbohydrates and IBS was identified some years ago by Australian doctors who developed the low FODMAP diet whereby fermentable oligosaccharides, disaccharides, monosaccharides and polyols are reduced or eliminated from the diet. These carbohydrates include fructose (found in certain fruits like apples, mangoes, watermelon and dried fruits), lactose (found in milk and milk products), fructans (found in wheat, garlic and onions), galactans (found in legumes) and polyols (found in fruits such as peaches and certain vegetables such as mushrooms and cauliflower). The low FODMAP diet is challenging to follow and ideally should be supervised by a dietician.

In summary, in individuals with symptoms related to ingestion of carbohydrates, assessment by a gastroenterologist or dietician, hydrogen breath testing and dietary manipulation may be of benefit.

If you have any questions about carbohydrates and maldigestion, please do not hesitate to contact Dr. Harris.