Fructose Intolerance — Are There Foods to Avoid?

Studies demonstrate that 35%-75% of the population may have fructose intolerance. Do you feel bloated, gassy, or have belly pain after eating certain foods? For some people, the foods we eat do not agree with us and aren’t being metabolized (broken down) properly. Many of us have a controversial opinion about simple carbohydrates, in other words, simple sugars.

Key takeaways:
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    Sugars come in many forms, occur naturally in foods, or are added for flavoring.
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    Some people can’t digest certain sugars, such as fructose, leading to food intolerances.
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    Fructose intolerance occurs due to a genetic mutation or arises secondary to underlying GI conditions such as irritable bowel syndrome, leaky gut syndrome, or bacterial overgrowth.
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    Diagnosing fructose intolerance can be fraught with difficulties.
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    Diet elimination trials help firm up a diagnosis even in the face of a negative test.

Some of us have issues with overeating, which goes to our hips. In contrast, others, like those with fructose intolerance, cannot metabolize the sugar properly and develop GI signs, including bloating, excess gas, and soft stool.

What is fructose?

Fructose is a simple sugar found in fruits and other plants. While you aren’t likely to run across the terms monosaccharides and disaccharides in your everyday lives, you likely have heard of glucose and fructose or monosaccharides and sucrose (a disaccharide is made by combining glucose and fructose). These are natural sugars found in various foods and added to many things to sweeten them or to add flavor. However, each individual breaks down these sugars differently.

Several foods naturally contain fructose, a 6-carbon monosaccharide molecule. Certain fruits, vegetables, and honey are examples of foods rich in fructose. However, it may also be manufactured enzymatically from corn to make high-fructose corn syrup (HFCS), which is frequently used in various sweeteners and soft drinks.

What is fructose intolerance?

Fructose intolerance is the inability to digest fructose. This condition can lead to clinical signs of an upset GI system and even sluggishness and pain.

Humans can absorb and process only specific amounts of fructose. When the ingested level exceeds the body’s ability to process the sugar, symptoms of fructose intolerance may manifest. However, how much fructose triggers signs differs from one person to another. When too much fructose remains in the gut undigested, it creates an osmotic effect. This causes water to be released into the intestines, causing digesting food to move more rapidly into the colon. Once in the colon, bacteria use it as food, producing excess gas, belly pain, and bloating.

Causes of fructose intolerance

Several studies over the past 20 years demonstrate two basic causes of fructose intolerance. One form occurs secondary to a genetic predisposition. Here, a person lacks a specific liver enzyme (aldolase B) that helps break down fructose. The other, fructose malabsorption or incomplete absorption, results when a person’s gut cannot transport all fructose across the gut wall into the cells. The latter arises in several GI conditions, such as irritable bowel syndrome (IBS) or small intestinal bacterial overgrowth (SIBO).

Symptoms of fructose intolerance

Symptoms of fructose intolerance vary from individual to individual. However, a combination of the following signs may appear.

  • Abnormal intestinal function
  • Nausea
  • Belly pain
  • Bloating (abdominal distension with or without pain)
  • Gas (flatulence)
  • Soft stool or other changes in stool consistency and quality
  • Gastroesophageal reflux (less often)

People who lack the enzyme needed to break down fructose (those with hereditary intolerance) may also suffer additional signs, including vomiting, belly pain, sweating, and low blood sugar (hypoglycemia). Further problems may include poor growth (kids), abnormalities in clotting blood (coagulation problems), constipation, enlarged liver, kidney issues, sleepiness, and even seizures.

Diagnostic testing

One would think that fructose intolerance would be easy to identify, right? Sadly, as with many gut disorders, a test does exist, but for a percentage of the population, it is either inconclusive or non-diagnostic and may leave a person wondering. So a negative test doesn’t rule out intolerance, but a positive may make one more likely to suffer from fructose intolerance.

Fructose intolerance testing: breath test

Tests can be done by looking at the amount of hydrogen (H2) and/or methane (CH4) one breathes out after ingesting a carbohydrate, like fructose. However, H2 and CH4 aren’t produced by humans but by the bacteria in one’s digestive tract. They are then breathed out or released as flatulence. Intestinal gases, such as H2 or CH4, arise from four sources:

Interested in learning more about breath tests? Check out the following:

It would be great if a positive result meant you have a disorder and a negative one declared you didn’t. However, the breath tests have limitations clouding the ability to diagnose this disease properly.

Breath test limitations include variable testing protocols. Using fructose as a liquid dose without other forms of sugar, like glucose on board, and after fasting often leads to false positive results (overdiagnosis). Only testing for H2 and not other gases could lead to underdiagnosis. Finally, a positive breath test and clinical signs, while one would assume causation (meaning the positive test and the symptoms indicate the fructose causes them, cannot easily be proven or reproducible in clinical studies). Studies suggest that people who failed to produce excess H2 or CH4 during the test but demonstrated problems, such as bloating, and abdominal pain, were considered positive.

Before embarking on a restrictive diet trial or other medical therapy, having some evidence suggestive of this disease may help you determine your next step. A combination of clinical symptoms, discomfort level, suspicion, and test results will help you and your doctor diagnose or rule out fructose intolerance.

Managing fructose intolerance with a diet

The primary treatment for fructose intolerance is diet restriction. However, people with underlying conditions, including a history of an eating disorder, may not be candidates for a proper elimination diet. Thus, before restricting your diet, talk with a healthcare provider and consider a registered dietician to help you plow through the various apps and options for fructose-free alternatives.

Determine your limit. Some people may not tolerate a hint of fructose before clinical side effects manifest. At the same time, others may be able to eat small amounts without ill effects.

Elimination diet trial

So, you are diagnosed with fructose intolerance; now what? An elimination diet trial such as the Low FODMAP Diet has scientific evidence to support research, fructose content found in foods, and proper elimination and reintroduction phases.

FODMAPs, or Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols, represent the naturally occurring carbohydrates in various foods. These sugars are often added to foods as flavorings and sweeteners, altering taste and selling products, even if the result may be less than healthy.

In addition, resources such as the Monash App and their website, and various other resources help one navigate the shopping markets, labels, and more to help through the process.

Where to start? Begin by eliminating all foods containing fructose for 4-8 weeks. This period allows symptoms to resolve fully and gives the healthy gut bacteria time to repopulate. After this time, slowly reintroduce foods with fructose and adjusts portion size to test your tolerance level.

Diet restrictions for fructose intolerance address carbohydrates in the diet. You can generally still eat proteins and fats safely as long as you have no other medical conditions that warrant changes. However, only carbohydrates contained in foods will have fructose.

Is high-fructose corn syrup bad for you?

Gibson et al. 2005 note that studies over the years have suggested that fructose may be one of the underlying causes of IBS. That's because researchers agree that it plays a role in fatty liver disease in alcoholics, worsens the US obesity epidemic, and contributes to the formation of dental disease.

Trends in the US show less intake of naturally occurring fructose foods while also seeing an overall increase in fructose consumption with high-fructose corn syrup (HFCS). Compared with sucrose, HFCS is cheaper but still sweetens food and drinks. When eaten in significant quantities, any individual can develop malabsorption or intolerance even when not predisposed. So, yes, HFCS can have negative health effects.

Foods containing fructose

Examples of foods with excess fructose include the following:

Fruits

  • Apples
  • Mango
  • Pears
  • Cherries

Vegetables

  • Asparagus
  • Broccoli
  • Sugar snap peas
  • Jerusalem artichokes

Sweeteners

  • Light and dark agave syrup
  • HFCS
  • Honey

The low FODMAP diet

Many people are surprised at how many types of sugars there are and how many foods naturally contain one or more of these sugars. We think fruits and vegetables are all healthy, right? The quick answer is, "Yes, they can be." However, various healthy foods contain natural sugars. Some people cannot properly break down one or more of these sugars to use as energy or properly metabolize them. As a result, they can make some of them sick.

FODMAPs is a generalized term encompassing poorly-absorbed sugar alcohols and short-chain carbohydrates (sugars), of which fructose is one of them. While the diet addresses five categories of carbohydrates that people may have trouble with, so if you are concerned with fructose, that is what you focus your efforts on restricting.

Non-diet therapies

Diet is the mainstay of therapy — avoiding fructose-containing foods is key. Other treatments currently being investigated in managing this condition include supplements that include xylose isomerase, an enzyme (not produced by humans) known to change fructose into glucose. Still, minimal studies exist, and more research is needed to determine both benefits and risks. Various supplements are out there but always talk with a healthcare provider before starting any over-the-counter products to ensure sufficient research supports their use and product safety.

Ignoring signs of fructose intolerance

Some individuals may have trouble processing certain foods, and some have trouble with carbohydrates, specifically fructose. Proper diagnosis can be difficult but occurs via a combination of history, signs, symptoms, and breath testing. An elimination trial may further help determine foods that are tolerated and those that flare signs.

People without the enzyme to break down fructose properly (hereditary intolerance) must prohibit fructose intake. However, for those without the genetic form of this condition, we appreciate clinical signs when fructose coexists in a food or group of foods in excess of glucose. By limiting one’s fructose intake or completely eliminating it for a while until symptoms subside, one can theoretically determine the source of the problem and avoid those foods in the future. This should minimize pain, bloating, and excess gas production and allow for a normal life even though without a few fruits and vegetables that contain fructose.

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