Symptoms and Management of Fructose Malabsorption

Dr. Christopher McGowan
December 8, 2020

Stomach problems are a pretty common occurrence for most of us. Maybe you ate too much on Thanksgiving, or maybe you ate something that didn’t agree with you, or maybe you have a more complicated condition like irritable bowel syndrome. The truth is that an upset stomach can be a symptom of many different maladies, but one that often gets overlooked is called fructose malabsorption.  

What is Fructose?

To really understand fructose malabsorption, it’s helpful to first look at what fructose actually is. Fructose is also sometimes known as fruit sugar because, unsurprisingly, it is a monosaccharide sugar found in fruits and many other types of plants. Unlike the complex sugars in our favorite sweet foods (and lots of other processed foods), fructose is a simple sugar. While simple sugars are named such because of their molecular structure, in practical terms, simple sugars like fructose are also much more easily digested. In fact, ingested fructose gets absorbed directly into the bloodstream from the small intestine, as opposed to complex sugars that have to be further broken down before the components can be used by the body. 

What is Fructose Malabsorption?

It’s important to note that fructose malabsorption shouldn’t be confused with a similarly named condition, hereditary fructose intolerance (HFI). HFI is a markedly different condition that is defined by an inborn malfunction of the metabolism related to the enzyme aldolase B. Normally when fructose is ingested, the aldolase enzyme binds to the fructose and allows it to be used as energy. In people with HFI, however, that enzyme is blocked and a resulting buildup of fructose-1-phosphate over time can lead to liver damage and even potentially death. Fructose malabsorption was actually originally referred to as dietary fructose intolerance (DFI), but it has been changed in order to more clearly distinguish between the two conditions. 

In fructose malabsorption, fructose is also unable to be properly absorbed by the digestive system. In this case, however, the reason is a problem with the cells that line the inner wall of the small intestine. These cells, known as enterocytes, are the primary way that nutrients are absorbed from broken down food and then carried around the body via the bloodstream. In people who have fructose malabsorption, the digestive system can only absorb a small amount of fructose. While problematic, fructose malabsorption is not nearly as dangerous as HFI because of a lack of toxic buildup in the liver. 

The fructose that isn’t absorbed by the small intestine becomes fermented by intestinal bacteria, causing a variety of gasses and short-chain fatty acids to be produced. It is this extraneous fermented fructose that is responsible for the symptoms associated with fructose malabsorption. These symptoms can include many of the symptoms like diarrhea and bloating that are shared by other gastrointestinal disorders like IBS, inflammatory bowel disease (IBD), or even lactose intolerance. As a result, fructose malabsorption can be difficult to accurately diagnose without a detailed exam by a gastroenterologist. Below are some of the common symptoms patients have reported: 

  • abdominal pain 
  • diarrhea 
  • bloating
  • flatulence 
  • nausea
  • vomiting 
  • fatigue
  • constipation

What Causes Fructose Malabsorption? 

As with many gastrointestinal problems, the cause of fructose malabsorption isn’t entirely clear, but it likely involves a combination of genetics, diet, and lifestyle factors. People who already have another digestive disorder seem to be more likely to develop fructose malabsorption, but there isn’t enough evidence that the relationship is causal. In general, medical conditions that can cause damage to the lining of the intestines are the likeliest reason for why the enterocytes in the small intestine can malfunction. Celiac disease, an autoimmune disorder related to the lining of the small intestine, is for this reason believed to be another possible cause. 

How is Fructose Malabsorption Treated?  

Unfortunately, there is no known cure for fructose malabsorption, so treatment generally revolves around easing the symptoms and reducing the amount of fructose that is ingested. For the most part, this means adapting one’s diet so that less fructose is consumed by simply avoiding foods with a high fructose content. But it can also mean being more strategic with food choices. As an example, and for reasons that aren’t fully understood, fructose is more easily digested when paired with glucose. So a person with fructose malabsorption could potentially be fine with eating a banana (which has roughly equivalent amounts of fructose and glucose) but should avoid eating an apple (which is high in fructose and low in glucose). 

Beyond a fructose-free diet, the research is still nascent in terms of other methods for treating fructose malabsorption. An alternative treatment option that has some initial promise is the use of the enzyme xylose isomerase as a dietary supplement. Found in many species of bacteria, this enzyme is capable of converting fructose into glucose, and some preliminary research has shown that it can improve the ingestion of fructose in people with the disorder. More research will need to be done to verify the efficacy. Other research has indicated that supplements used for IBS patients may also have a positive impact on fructose malabsorption.  

Foods to Avoid 

For people who are experiencing gastrointestinal discomfort because of fructose malabsorption, it’s important to be aware of foods to avoid that have a high fructose content. While there isn’t really any danger in eating these foods and ingredients, your digestive tract will thank you if you steer clear of them: 

  • Non-diet sodas 
  • Certain fruits: apples, pears, plums, watermelon, cherries, prunes, mango
  • Certain dried fruits: dates, figs, raisins, sultanas, currants
  • Certain vegetables: sugar snap peas, leeks, cabbage, lettuce, broccoli, onions
  • Apple juice 
  • Honey
  • Foods with high fructose corn syrup as a sweetener 
  • Agave nectar 
  • Ginger
  • Sorbitol 
  • Xylitol 

One other way to categorize the foods to avoid is through what’s known as a low FODMAP diet. FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols; more simply, this complicated term refers to foods that are especially prone to fermentation in the large intestine. While the connection between a FODMAP diet and fructose malabsorption isn’t direct, it is a good place to start for modifying one’s diet. The American College of Gastroenterology fortunately offers a list of such foods to avoid. 

In avoiding all these types of foods that contain fructose, many people turn to artificial sweeteners like aspartame and sucralose. In addition to sorbitol and xylitol, another artificial sweetener that is especially good to avoid is the sugar alcohol erythritol. Recent studies have indicated that erythritol can actually promote malabsorption. Moreover, erythritol as an additive, when combined with fructose, can actually cause gastrointestinal symptoms like watery stools. Being able to identify and avoid such additives requires a person with fructose malabsorption to be vigilant about reading labels on foods to learn the ingredients.  

Foods That are Acceptable 

As important as it is to avoid certain foods, it is also beneficial to be aware of foods that are suitable for consumption with fructose malabsorption. Below is a list of a few examples of foods that have a low fructose content and/or a favorable ration between fructose and glucose: 

  • Fruits: bananas, blueberries, lemons, limes, cantaloupe, strawberries
  • Vegetables: bean sprouts, bell peppers, carrots, potatoes, spinach
  • Artificial Sweeteners: aspartame, sucralose
  • Gluten-free breads, pastas, cereals
  • Eggs
  • Nuts, seeds

Making Better Food Choices

Fructose malabsorption is a relatively mild condition, but solving the ongoing discomfort requires thinking a bit more strategically about what you’re eating. The same principle is true, however, for anyone who wants to improve their health or even lose weight. The average American diet has an outsized amount of sugar whether it be fructose, glucose, or sucrose, the more medically concerning table sugar that is used to sweeten everything from cakes to ice cream to pasta sauce. 

For most people, changing one’s diet is synonymous with being “on a diet” in order to lose weight. But just relying on an elimination diet is rarely effective for those who are actually trying to lose weight. It’s for this reason that True You offers state-of-the-art weight loss procedures that are designed to help you go beyond just cutting back on carbohydrates and instead find a new way to live. If you’d like to learn more about what we offer, request a consultation today to speak with a dietitian. Freedom is waiting! 

Dr. Christopher McGowan
Dr. Christopher McGowan

Dr. Christopher McGowan, MD, a leader in endobariatrics, specializes in non-surgical obesity treatments and is triple-board-certified in Internal Medicine, Gastroenterology, and Obesity Medicine. Renowned for pioneering endoscopic sleeve gastroplasty (ESG) with over 2,000 procedures, his global influence and research contributions define him as a top expert.

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