Fructose and digestion: intolerance or malabsorption?
Fructose is a natural type of sugar that occurs in many fruits and plants. But have you ever wondered why a simple apple or a glass of lemonade can cause unpleasant symptoms in some people? The reason for that might be fructose. Read on if you want to learn more about the role of fructose in nutrition and why it is not equally digestible for everyone.
Table of Contents
- What is fructose?
- What is the difference between fructose intolerance and fructose malabsorption?
- What symptoms occur?
- How are these conditions diagnosed?
- Can fructose lead to fatty liver?
- Are there other complications?
- What treatment options are available?
- Is fructose intolerance the same as a fruit allergy?
- Summary
What is fructose?
Fructose, often referred to as "fruit sugar," is a naturally occurring sugar molecule found in a variety of foods, especially fruit. On a molecular level, fructose is one of the monosaccharides, the simplest form of sugar found in nature. Its structure allows the human body to use it directly without needing to break it down further. Fructose has a distinct sweetness, which has made it popular as a sweetener in the food industry. But despite its natural presence and sweet taste, fructose can be problematic for some individuals (Britannica, 2023).
Which foods contain fructose?
Although many people associate fructose directly with fruit, it occurs in an impressive variety of foods. Here are some prominent sources:
- Fruit: The amount of fructose can vary depending on the type of fruit. Apples and pears contain high levels of fructose, while berries generally have lower amounts.
- Vegetables: Some vegetables, such as asparagus, onions, and artichokes, also contain a notable amount of fructose.
- Sweeteners: Honey, agave syrup, and high-fructose corn syrup (HFCS) are rich in fructose. HFCS in particular is used in a variety of processed foods and beverages.
- Processed foods and drinks: Many industrially produced products, from soft drinks to cookies, contain varying amounts of fructose.
Source: Mayo Clinic, 2022
What is the difference between fructose intolerance and fructose malabsorption?
These terms are easily confused, but they refer to two different health conditions:
- Fructose intolerance (Hereditary Fructose Intolerance – HFI): Hereditary fructose intolerance (HFI) is inherited. It is a rare genetic disorder in which the liver cannot produce or use an enzyme called aldolase B. This enzyme is necessary to break down fructose. Consuming fructose can cause severe symptoms in affected individuals (MedlinePlus, 2011).
- Fructose malabsorption: This is a reduced ability of the small intestine to absorb fructose. When fructose is not absorbed in the small intestine, it reaches the large intestine, where it is fermented by bacteria (Vilines, 2023).
Sometimes fructose malabsorption is also called "fructose intolerance," which can be confusing. Fructose intolerance is a broader term that includes both hereditary fructose intolerance and fructose malabsorption. It refers to the inability to properly digest or absorb fructose. It is therefore important to understand the differences between these two conditions. While fructose intolerance is a genetic metabolic disorder, fructose malabsorption is a food intolerance.
What symptoms occur?
Fructose intolerance and fructose malabsorption are two distinct conditions with different causes and symptoms. While the symptoms of fructose malabsorption usually affect the digestive system, the symptoms of fructose intolerance can be more severe and affect other organs, especially the liver.
What symptoms are associated with fructose intolerance?
- Hypoglycemia (low blood sugar)
- Vomiting after meals containing fructose
- Growth disorders in children
- Enlarged liver
- Jaundice
- Upper abdominal pain
What symptoms are associated with fructose malabsorption?
- Flatulence
- Diarrhea or constipation
- Stomach cramps
- Nausea
- Bloating
- Fatigue after meals containing fructose
The severity of symptoms in both fructose malabsorption and fructose intolerance can be dose-dependent, meaning they often depend on the amount of fructose consumed.
Sources: Cleveland Clinic, 2021; Olsen, 2018
How are these conditions diagnosed?
Hereditary fructose intolerance can be diagnosed through a genetic test that detects specific genetic mutations. Additionally, enzyme activity tests from liver biopsies can provide indications of this disorder (NORD, 2007).
The most common method to diagnose fructose malabsorption is the hydrogen breath test after fructose ingestion. An increased concentration of hydrogen in the breath indicates insufficient absorption. Furthermore, elimination diets followed by provocation tests can be conducted to observe the body’s reaction to fructose (Benardout et al., 2021).
Can fructose lead to fatty liver?
Fructose can be metabolically converted in the liver into precursors of fat. Excessive intake of fructose can therefore promote fat accumulation in the liver and increase the risk of developing non-alcoholic fatty liver disease (NAFLD).
NAFLD is characterized by significant fat storage in the liver in the absence of elevated alcohol consumption. If left untreated, NAFLD can progress and lead to further liver complications such as liver inflammation or cirrhosis.
Consistently and excessively consuming fructose-containing products—especially beverages with added fructose—is therefore a modifiable risk factor for liver health issues (Harvard Health, 2011).
Are there other complications?
If left untreated, both conditions can lead to various health problems:
Fructose intolerance (hereditary)
- Hypoglycemia (low blood sugar)
- Liver damage (e.g., enlarged liver, liver cirrhosis)
- Kidney failure
- Nutritional deficiencies (e.g., lack of vitamins and minerals)
- Digestive issues (e.g., nausea, vomiting)
- Growth retardation in children
Fructose malabsorption
- Digestive complaints (e.g., flatulence, diarrhea, abdominal pain)
- Increased risk of irritable bowel syndrome (IBS)
- Imbalance in gut flora
- Deficiencies (e.g., due to limited absorption of vitamins and minerals)
Sources: Benardout et al., 2021; NORD, 2007
Want to get an overview yourself? Homediq’s tests make it easy to check your health status from home. In the context of fructose intolerance or malabsorption, tests such as the liver function test (to identify potential liver damage), the HbA1c blood sugar test (to monitor average blood sugar levels), and the vitamin deficiency test (to analyze vitamin status) are particularly relevant. These tests can help detect potential complications early and monitor overall health status.
What treatment options are available?
The treatment of fructose intolerance and fructose malabsorption focuses on relieving symptoms and preventing potential long-term damage. Although both conditions require dietary adjustments, the recommended treatment approaches differ.
General tips for both conditions
- Avoid industrially produced foods with a high fructose content, such as certain candies, soft drinks, and other sugary beverages.
- Read labels carefully to identify hidden sources of fructose or fructose syrup.
- Consider nutritional counseling to ensure your diet remains balanced and nutritious.
- Monitor your symptoms and consider keeping a food diary to identify specific triggers.
Treatment for fructose intolerance (Hereditary Fructose Intolerance – HFI)
For individuals with HFI, consuming fructose, sucrose (table sugar), and sorbitol can be potentially dangerous. Treatment primarily involves:
- Strict avoidance of fructose, sucrose, and sorbitol in the diet.
- Continuous monitoring and dietary adjustments, especially during illness or times of increased energy needs.
- Regular check-ups with a doctor to monitor liver function and blood sugar and uric acid levels.
Source: Cleveland Clinic, 2021
Treatment for fructose malabsorption
Here, the goal is primarily to reduce the amount of fructose consumed—not to eliminate it entirely.
- Elimination phase (also called the Strict Phase): In this phase, all fructose-containing foods are strictly avoided. The goal is to eliminate symptoms and give the intestines a break.
- Reintroduction phase (also called the Testing or Tolerance Determination Phase): After a symptom-free elimination phase, fructose-containing foods are gradually and systematically reintroduced into the diet. Careful observation is used to determine which amounts and foods trigger symptoms.
- Maintenance phase (also called the Adaptation or Stabilization Phase): A long-term diet is maintained based on individual tolerance levels. The FODMAP diet may be helpful here. FODMAP stands for “Fermentable Oligo-, Di-, Monosaccharides and Polyols.” These are a group of short-chain carbohydrates and sugar alcohols found in certain foods that can cause digestive problems in some individuals. The FODMAP diet restricts intake of these substances to reduce symptoms such as bloating, abdominal pain, or diarrhea.
Source: Benardout et al., 2021
If necessary, enzyme supplements or probiotics may also be considered to support digestion. While fructose intolerance requires strict dietary compliance, treatment for fructose malabsorption offers more flexibility once individual tolerance levels are identified. In both cases, close collaboration with a dietitian and physician is essential.
Is fructose intolerance the same as a fruit allergy?
Fructose intolerance and fruit allergy are two different conditions, though both can cause symptoms after eating fruit. While fructose intolerance results from the body’s inability to efficiently break down fructose, a fruit allergy is a food allergy involving an immune response to specific proteins in the fruit. An allergic reaction can cause rashes and respiratory problems or even lead to life-threatening conditions such as anaphylactic shock. It is important to distinguish between these two conditions and to consult a doctor if suspected (Cleveland Clinic, 2021).
Summary
Fructose intolerance is a hereditary metabolic disorder in which the liver cannot properly break down fructose, potentially leading to serious health complications. Fructose malabsorption, on the other hand, refers to the inability of the small intestine to efficiently absorb fructose, resulting in digestive complaints. Although diagnostic methods differ, dietary adjustment is central to managing both conditions, with the FODMAP diet proving especially useful for malabsorption.
