Fructose is the sugar found naturally in fruits, fruit juices, some vegetables and honey. Fructose is also one of the components in sugar (sucrose is made up of fructose and glucose), as well as high-fructose corn syrup (which is commonly used to sweeten many processed foods and beverages).
If you suffer from fructose malabsorption (aka fructose intolerance) your digestive system doesn’t absorb fructose properly. It is thought that up to 30% of the population suffer from it.
There is a rare inherited condition, which causes fructose intolerance, caused by the deficiency of a key enzyme in the liver that breaks it down (symptoms include; jaundice, vomiting, convulsions, failure to thrive and excessive sleepiness).
Alternatively secondary fructose malabsorption occurs when people are lacking a fructose transporter (known as GLUT5). GLUT5 carries fructose through the cells in the small intestines. The symptoms of this are; abdominal pain, bloating and wind, diarrhoea or constipation, chronic fatigue, low iron and other nutrients. Some may suffer headaches and occasionally depression as fructose malabsorption is linked to low tryptophan (tryptophan is the precurser to serotonin).
Primary Causes
SIBO – Small Intestinal Bacterial Overgrowth, occurs when opportunistic or pathogenic bacteria colonise the distal small intestine. This happens when there are changes in the type of bacteria present in the small intestine or when pre-existing bacteria proliferate due to favourable conditions. SIBO is thought to change the structure and function to gastric mucosa of the small intestine, causing an inability to properly transport sugars and may increase gut permeability (aka leaky gut). Causes of SIBO include GI surgery, malnutrition, immune deficiency, low stomach acid, IBS, multiple use of anti-biotics, H2 antagonist (anti histamine), long-standing coeliac disease, Crohn’s, Type 2 diabetes and PPI use.
Acute gastroenteritis – an infection in the gut may be behind the start of fructose malabsorption, with and without the use of anti-biotics.
Coeliac, IBS and Crohn’s disease
Due to the nature of these diseases causing damage to the gut lining, the absorption of carbohydrates become impaired.
Increased intestinal permeability (IP) – aka Leaky Gut
Intestinal permeability refers to gaps in the normally tight junctions between the cells that line the microvilli, allowing undigested food particles, toxins, pathogens and the like to cross over from the gut luemn into the blood stream – triggering inflammation and an immune response. Causes of IP include; medication use, poor nutrition, stress, coeliac disease, infections and pathogens, food allergies, as well as pre-existing fructose and lactose intolerance.
Compromised Gut Function
Reduced stomach acid and insufficient digestive enzymes are the main culprits in this situation. Low stomach acid means that food complexes are not broken down into their individual nutrient components and insufficient digestive enzymes affects nutrients to be effectively absorbed and assimilated.
Testing methods available;
- Hydrogen breath test for SIBO,
- Comprehensive Digestive Stool Analysis
- Intestinal Permeability testing.
Once gut repair is complete high FODMAP foods can be trialled and re-introduced successfully in many people.
Treatment;
Treatment for fructose intolerance includes reducing high-fructose foods, such as juices, apples, grapes, watermelon, asparagus, peas and zucchini, for a period of time. It’s not ideal to remove these foods permanently and with certain treatments these may be re-introduced in due course.