Fructose Intolerance

Introduction

Fructose, a type of sugar, occurs naturally in a variety of foods including fruits, the juices derived from them, select vegetables, and honey. This sweet substance also forms an essential part of table sugar, known scientifically as sucrose. Additionally, high-fructose corn syrup, a common sweetener, is extensively used in the sweetening of numerous processed foods and a wide range of beverages, contributing to their appealing taste.

If your body struggles to absorb fructose efficiently, it can lead to various digestive issues like abdominal discomfort, diarrhea, and bloating. Individuals with fructose intolerance need to be mindful of their diet, particularly limiting foods high in fructose. This includes a wide array of fruits, especially those that are dried or canned in juice or syrup, and many vegetables such as artichokes, asparagus, broccoli, leeks, mushrooms, okra, onions, peas, red peppers, shallots, and tomato-based products. Wheat-based foods, including wheat bread and pasta, are also significant sources of fructose. Sweeteners like honey, agave nectar, and high-fructose corn syrup, commonly found in many processed foods, should be consumed cautiously. Additionally, sodas and various desserts that are sweetened with fructose are items to be careful with in the diet of those who have fructose intolerance.

Thankfully, there are certain fruits that contain less fructose, offering better options for those with dietary fructose intolerance. These fruits, known for their lower fructose content, often are more tolerable for individuals managing this condition. The list of such fruits includes:

– Avocados, known for their creamy texture and nutritional value.

– Bananas, a versatile and easily digestible fruit.

– Cranberries, both tart and flavorful.

– Cantaloupe, a type of melon with a distinctively sweet taste.

– Lemons and limes, which are more citrusy and less sweet.

– Oranges, offering a perfect blend of tang and sweetness.

– Pineapple, known for its tropical flavor.

– Strawberries, with their delightful balance of sweetness and acidity.

In addition to these fruits, there are other foods low in fructose that might be better tolerated when eaten in moderation and preferably with meals. These include bananas, blueberries, strawberries, carrots, avocados, green beans, and lettuce. Each of these offers a combination of nutritional benefits and lower fructose levels, making them potentially suitable for those with dietary fructose intolerance.

Types of fructose intolerance

There are three types of fructose intolerance.

Fructose malabsorption

Fructose malabsorption, a prevalent food sensitivity, impacts approximately 40% of individuals in Western regions. This condition, like other food sensitivities, may arise from a complex interplay of various factors including genetic predisposition, lifestyle habits, the degree of exposure to fructose, and the general state of health. In those affected by fructose malabsorption, the body is unable to effectively absorb or process fructose. Consequently, this unabsorbed fructose travels into the large intestine, leading to the production of gas and resulting in uncomfortable and often painful digestive symptoms. This condition highlights the need for careful dietary management and awareness of fructose intake for those susceptible.

Individuals with fructose malabsorption may also experience sensitivities to a broader category of foods known as FODMAPs, an acronym that stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These substances, which encompass a range of both natural and artificial sweeteners, can be particularly challenging for people with fructose malabsorption. FODMAPs are found in a wide variety of foods and can contribute to digestive discomfort when consumed by those with sensitivities to these compounds. This group includes various types of sugars and sweeteners, which, due to their fermentable nature, can exacerbate symptoms in sensitive individuals. Managing a diet that takes into account both fructose malabsorption and FODMAP sensitivity requires careful consideration of the types and amounts of foods consumed.

Essential Fructosuria

Essential fructosuria, or hepatic fructokinase deficiency, is a harmless recessive disorder that a person may have without knowing. If a condition is recessive, it means that a child will only have it if they receive the gene from both parents. If they receive the gene from one parent but not the other, they will be a carrier.

People with essential fructosuria lack a liver enzyme called hepatic fructokinase that can break down fructose. Essential fructosuria is not harmful. People with this condition are typically asymptomatic and do not need treatment.

Hereditary fructose intolerance

Hereditary fructose intolerance is a serious type of fructose intolerance. However, it is treatable and manageable. It occurs when a person cannot digest fructose and fructose precursors such as brown sugar.

Those with hereditary fructose intolerance lack sufficient activity of an enzyme that helps digest fructose called fructose-1-phosphate aldolase.

The undigested fructose accumulates in the liver and kidneys. This may lead to serious and even life threatening complications such as liver failure and kidney failure.

Hereditary fructose intolerance is a condition that affects a person’s ability to digest the sugar fructose. Fructose is a simple sugar found primarily in fruits. Affected individuals develop signs and symptoms of the disorder in infancy when fruits, juices, or other foods containing fructose are introduced into the diet. After ingesting fructose, individuals with hereditary fructose intolerance may experience nausea, bloating, abdominal pain, diarrhea, vomiting, and low blood sugar (hypoglycemia). Affected infants may fail to grow and gain weight at the expected rate (failure to thrive).

Repeated ingestion of fructose-containing foods can lead to liver and kidney damage. The liver damage can result in a yellowing of the skin and whites of the eyes (jaundice), an enlarged liver (hepatomegaly), and chronic liver disease (cirrhosis). Continued exposure to fructose may result in seizures, coma, and ultimately death from liver and kidney failure. Due to the severity of symptoms experienced when fructose is ingested, most people with hereditary fructose intolerance develop a dislike for fruits, juices, and other foods containing fructose.

Hereditary fructose intolerance should not be confused with a condition called fructose malabsorption. In people with fructose malabsorption, the cells of the intestine cannot absorb fructose normally, leading to bloating, diarrhea or constipation, flatulence, and stomach pain. Fructose malabsorption is thought to affect approximately 40 percent of individuals in the Western hemisphere; its cause is unknown.

Frequency

The incidence of hereditary fructose intolerance is estimated to be 1 in 20,000 to 30,000 individuals each year worldwide.

Causes

Mutations in the ALDOB gene cause hereditary fructose intolerance. The ALDOB gene provides instructions for making the aldolase B enzyme. This enzyme is found primarily in the liver and is involved in the breakdown (metabolism) of fructose so this sugar can be used as energy. Aldolase B is responsible for the second step in the metabolism of fructose, which breaks down the molecule fructose-1-phosphate into other molecules called glyceraldehyde and dihydroxyacetone phosphate.

ALDOB gene mutations reduce the function of the enzyme, impairing its ability to metabolize fructose. A lack of functional aldolase B results in an accumulation of fructose-1-phosphate in liver cells. This buildup is toxic, resulting in the death of liver cells over time. Additionally, the breakdown products of fructose-1-phosphase are needed in the body to produce energy and to maintain blood sugar levels. The combination of decreased cellular energy, low blood sugar, and liver cell death leads to the features of hereditary fructose intolerance.

You have a 25% chance of developing hereditary fructose intolerance if both of your parents have the gene that causes aldolase B not to work.‌

If you eat foods that have fructose or sucrose, another kind of sugar, your body can’t change stored sugar into glucose. This causes your blood sugar to crash and toxins can build up in your liver.

Fructose malabsorption develops when you’re an adult. This is one of the differences between the two types of fructose intolerance. Fructose malabsorption can be due to many causes that include:

imbalance of good and bad bacteria in the gut

high intake of refined and processed foods

preexisting gut issues such as irritable bowel syndrome (IBS)

inflammation

Stress

Risk factors

If you have certain gut disorders such as IBS, Crohn’s disease, colitis, or celiac disease, Gastroenteritis you’re more likely to have dietary fructose malabsorption or intolerance. Use of antibiotics also make one more prone to the intolerance.

Inheritance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Symptoms

Symptoms can be seen after a baby starts eating food or formula.

The early symptoms of fructose intolerance are similar to those of galactosemia (inability to use the sugar galactose). Later symptoms relate more to liver disease.

Symptoms may include:

Convulsions

Excessive sleepiness

Irritability

Yellow skin or whites of the eyes (jaundice)

Poor feeding and growth as a baby, failure to thrive

Problems after eating fruits and other foods that contain fructose or sucrose

Vomiting

Hereditary Fructose Intolerance

Most people with this inherited form of fructose intolerance start showing signs as a baby. New cases are rarely diagnosed in adults. Infants often have symptoms of intolerance as soon as they are introduced to foods that contain fructose. Some common symptoms include:

Jaundice

Stunted growth

Vomiting

Bloating

A decrease of phosphate and glucose in the blood

An increase in fructose in the urine and blood

Nausea

Abdominal pain

Dislike of fruit or sweet things

Dietary Fructose Intolerance

Malabsorbed fructose refers to fructose that hasn’t been digested completely. It ferments in your lower bowels. You may experience symptoms similar to those of irritable bowel syndrome (IBS) when you eat foods with a lot of fructose, such as:

Bloating

Gas

Diarrhea

Stomachaches

nausea

vomiting

chronic fatigue

malabsorption of certain nutrients, such as iron

Exams and Tests

Physical examination may show:

Enlarged liver and spleen

Jaundice

Tests that confirm the diagnosis include:

Blood clotting tests

Blood sugar test

Enzyme studies

Genetic testing

Kidney function tests

Liver function tests

Liver biopsy

Uric acid blood test

Urinalysis

The first test is a liver biopsy, which can confirm a deficiency of aldolase, indicating a fructose intolerance. The second is a feeding test, during which a doctor delivers fructose through an IV needle. They then assess the body’s response to this sugar.

A hydrogen breath test is a common test used to diagnose issues with digesting fructose. It’s a simple test that doesn’t involve a blood draw. You’re required to limit carbohydrates the night before and fast the morning of the test.

A doctor may also use the elimination diet to diagnose malabsorption. With an elimination diet, a person avoids all foods containing fructose and other potential allergens and then monitors the results.

A doctor can perform two diagnostic tests to determine whether a baby has hereditary fructose intolerance. Blood sugar will be low, especially after receiving fructose or sucrose. Uric acid levels will be high.

Treatment

Removing fructose and sucrose from the diet is an effective treatment for most people. Complications may be treated. For example, some people can take a medicine to lower the level of uric acid in their blood and decrease their risk for gout.

Outlook (Prognosis)

Hereditary fructose intolerance may be mild or severe.

Avoiding fructose and sucrose helps most children with this condition. The prognosis is good in most cases.

A few children with a severe form of the disease will develop severe liver disease. Even removing fructose and sucrose from the diet may not prevent severe liver disease in these children.

How well a person does depends on:

How soon the diagnosis is made

How soon fructose and sucrose can be removed from the diet

How well the enzyme works in the body

Possible Complications

These complications may occur:

Avoidance of fructose-containing foods due to their effects

Bleeding

Gout

Illness from eating foods containing fructose or sucrose

Liver failure

Low blood sugar (hypoglycemia)

Seizures

Death

When to Contact a Medical Professional

Contact your health care provider if your child develops symptoms of this condition after feeding starts. If your child has this condition, experts recommend seeing a doctor who specializes in biochemical genetics or metabolism.

Prevention

Couples with a family history of fructose intolerance who wish to have a baby may consider genetic counseling.

Most of the damaging effects of the disease can be prevented by decreasing fructose and sucrose intake.

Other questions

What Is Fructose?

Fructose is a type of simple sugar that makes up 50% of table sugar (sucrose). Table sugar also consists of glucose, which is the main energy source for your body’s cells. However, fructose needs to be converted into glucose by the liver before it can be used by the body.

Can you suddenly develop fructose intolerance?

Hereditary fructose intolerance and essential fructosuria are inherited conditions that don’t develop suddenly. Fructose malabsorption may develop from conditions that affect the intestines, such as acute gastroenteritis, IBD, or a high fructose diet.

What happens if you are fructose intolerant?

With fructose malabsorption or essential fructosuria, a person may have symptoms that ease with diet changes. Hereditary fructose intolerance must be treated by a doctor, because it can be life threatening.

What is the difference between dietary and hereditary fructose intolerance?

Dietary vs. Hereditary fructose intolerance:

Fructose intolerance can be classified as either hereditary or dietary fructose intolerance.

Hereditary fructose intolerance is caused by rare mutations in the ALDOB gene and is present from birth.

Dietary fructose intolerance shares some of the symptoms of hereditary fructose intolerance, but the disorder is caused by decreased fructose absorption in the small intestine.

 Is fructose intolerance the same as hereditary fructose intolerance (HFI)?

   – No, HFI is a severe genetic disorder, while fructose intolerance can have various causes, including acquired deficiencies of the necessary enzymes.

Can fructose intolerance develop later in life?

   – Yes, fructose intolerance can develop at any age, although it is often identified in childhood.

Are artificial sweeteners safe for those with fructose intolerance?

    – Some artificial sweeteners, like sorbitol and mannitol, can worsen symptoms and should be avoided.

Can fructose intolerance lead to nutritional deficiencies?

    – Prolonged untreated fructose intolerance may lead to nutritional deficiencies due to malabsorption of essential nutrients.

Can fructose intolerance cause weight loss?

    – Unintentional weight loss can occur if symptoms are severe and lead to reduced food intake.

Can fructose intolerance cause skin rashes or hives?

    – While gastrointestinal symptoms are more common, some individuals may experience skin issues as a result of fructose intolerance.

Can fructose intolerance lead to liver problems?

    – Severe, untreated fructose intolerance may cause liver damage over time in some cases.

Can fructose intolerance be managed with dietary supplements?

    – While supplements may help address nutritional deficiencies, the primary treatment for fructose intolerance is a low-fructose diet and enzyme replacement therapy if necessary.

Myths and facts

Myth 1: Fructose intolerance is the same as a fructose allergy.

Fact 1: Fructose intolerance is a metabolic disorder, while a fructose allergy is an immune response. They are distinct conditions with different underlying mechanisms.

Myth 2: Fructose intolerance is rare.

Fact 2: Fructose intolerance is more common than once believed and often goes undiagnosed. It varies in prevalence depending on the population studied.

Myth 3: All fruits are off-limits for people with fructose intolerance.

Fact 3: While some fruits are high in fructose and may trigger symptoms, others are lower in fructose and may be tolerated in moderation.

Myth 4: A small amount of fructose won’t cause symptoms.

Fact 4: Even small amounts of fructose can trigger symptoms in individuals with fructose intolerance, as the threshold for tolerance varies from person to person.

Myth 5: Fructose intolerance is the same as lactose intolerance.

Fact 5: Fructose intolerance and lactose intolerance are distinct conditions. Lactose intolerance is the inability to digest lactose, a sugar found in dairy products, while fructose intolerance involves difficulty in metabolizing fructose, a sugar found in many fruits, vegetables, and sweeteners.

Myth 6: Artificial sweeteners are safe for individuals with fructose intolerance.

Fact 6: Some artificial sweeteners, like sorbitol and mannitol, can exacerbate symptoms in individuals with fructose intolerance as they are sugar alcohols that the body may have difficulty processing.

Myth 7: Fructose intolerance only affects the digestive system.

Fact 7: Fructose intolerance can have systemic effects and may lead to other health issues if not managed properly.

Myth 8: A low-fructose diet is the only treatment for fructose intolerance.

Fact 8: While dietary modifications are a key part of managing fructose intolerance, other factors such as enzyme replacement therapy may be considered in some cases.

Myth 9: Fructose intolerance is a lifelong condition.

Fact 9: Some individuals with fructose intolerance may outgrow the condition, especially if it is due to a transient issue or a secondary condition.

Myth 10: Fructose intolerance is the same as hereditary fructose intolerance (HFI).

Fact 10: Hereditary fructose intolerance (HFI) is a severe genetic disorder caused by a deficiency of the enzyme aldolase B. It is distinct from non-hereditary forms of fructose intolerance.

Myth 11: Fructose intolerance only affects children.

Fact 11: Fructose intolerance can develop at any age, and its onset is not limited to childhood.

Myth 12: Fructose intolerance is not a serious condition.

Fact 12: Untreated fructose intolerance can lead to chronic health issues and discomfort. It should be taken seriously and managed appropriately.

Myth 13: Fructose intolerance is the same as irritable bowel syndrome (IBS).

Fact 13: Fructose intolerance and IBS are separate conditions, although they share some similar symptoms. It’s possible for individuals to have both conditions simultaneously.

Myth 14: Fructose intolerance can be diagnosed through a simple blood test.

Fact 14: Diagnosis typically involves a combination of medical history, symptom assessment, and hydrogen breath tests, as well as response to dietary changes.

Myth 15: People with fructose intolerance must avoid all high-fructose foods entirely.

Fact 15: The severity of fructose intolerance varies among individuals, and some may tolerate small amounts of high-fructose foods without symptoms, while others may need to avoid them entirely. Individualized dietary plans are important.