Carbohydrate Intolerances

In medical terminology, carbohydrate intolerances generally refer to chronic abdominal complaints that occur after consuming foods containing lactose, fructose, or other mono- and disaccharides. The symptoms often resemble irritable bowel syndrome (IBS) and usually result from the body's inability to adequately digest and absorb these carbohydrates in the intestine.

A more clinically accurate term for the impaired utilization of these sugar molecules is carbohydrate malassimilation. This umbrella term includes two types of dysfunctions based on the underlying cause:

• Maldigestion: caused by reduced enzymatic activity in breaking down complex sugars (e.g. lactose intolerance)
• Malabsorption: due to limited intestinal capacity to absorb carbohydrates (e.g. fructose intolerance)

Lactose (milk sugar) is a disaccharide naturally found in milk and dairy products. It cannot be absorbed directly by the small intestine and must first be split by the enzyme lactase into its components glucose and galactose. These monosaccharides can then be absorbed into the bloodstream via the lining of the small intestine. Lactose intolerance occurs when lactase activity is reduced or entirely absent.

There are two types:

• Primary lactose intolerance: genetically determined
• Secondary lactose intolerance: caused by an underlying condition which damages the lining of the small intestine, and can potentially be reversed with treatment

Fructose malabsorption is even more common in Central Europe than lactose intolerance. Around 30 to 40% of the population experience delayed fructose transport across the intestinal wall. This is usually due to a dysfunction of the GLUT-5 (glucose transporter 5) protein in the small intestine. Stress and elevated glucocorticoid levels can also inhibit fructose uptake.

Sorbitol is a sugar alcohol derived from glucose via catalytic hydrogenation and is converted into fructose in the body. It naturally occurs in many fruits but is also used by the food industry as a sweetener, carrier, or humectant (E number 420).

Isomaltose, like sucrose (table sugar), is a disaccharide. It occurs naturally in honey and is also produced during the digestion of starch and glycogen in the intestine. Sucrose/isomaltase deficiency is caused by a genetic defect that results in reduced activity of the enzyme sucrase-isomaltase.

Excess unabsorbed sugars undergo bacterial fermentation in the large intestine, which leads to the production of gases such as hydrogen, carbon dioxide, and methane. This typically causes symptoms 30 minutes to 3 hours after consuming problematic foods:

• Flatulence
• Abdominal pain
• Stomach pain

Symptoms may vary in severity and frequency depending on the amount and type of carbohydrate consumed.

Breath Test Analysis

Diagnosis of carbohydrate malassimilation is carried out non-invasively by using challenge tests and measurement of hydrogen (H₂) – a by-product of bacterial fermentation – in exhaled breath.

How the H₂ breath test works:

After ingestion of a solution containing a defined amount of the relevant carbohydrate, breath samples are collected at specific intervals. The hydrogen concentration in the exhaled air is then analyzed in the lab.

• Healthy individuals show no increase in H₂ or symptoms after ingestion.
• Individuals with carbohydrate intolerance exhibit a significant rise in H₂ levels over time, usually after 60 to 90 minutes, depending on the sugar tested.

Note: 10 to 25% of the European population are H₂ non-responders, which means that they do not show increased H₂ levels in the breath test despite having functional malassimilation.

Genetic Testing

Genetic testing can also be conducted to identify primary (hereditary) forms of sucrose/isomaltose, fructose, or lactose intolerance. This involves analyzing the relevant genes for known mutations.