Is Fructose Malabsorption Causing Your IBS?

brightly colored fruit that causes fructose malabsorption

Tummy troubles? Bloating, diarrhea, cramping, pain, indigestion, or constipation?

How can you figure out if fructose is irritating your innards?

If it is fructose, what should you eat to make your symptoms go away?

If it's not fructose, what are the other foods that could be your culprits?

[This is article four of a five-part series about fructose. If you’d like to start at the beginning and read about what fructose is and how the body processes it differently from glucose, please see article one: "Has Fructose Been Framed?"]

What is fructose malabsorption?

As we saw in the first three articles of this series, generally speaking, excess glucose is more dangerous to your health than excess fructose, but there is one important exception: fructose malabsorption. If you have bouts of unhappy digestion, you could have fructose malabsorption and not realize it. The final article in this fructose series, coming later this month, will explore how much fructose and glucose is safe for us to eat and how to prevent/improve insulin resistance and common diseases, but I think fructose malabsorption deserves its own post…and some pretty charts to boot!

We easily and completely absorb 100% of the glucose we consume, except for the 4% of us who have small intestinal bacterial overgrowth or SIBO but most of us have trouble absorbing fructose. In clinical studies, anywhere between 10% and 50% of us can’t completely absorb 25 grams of fructose, and up to 80% of us can’t absorb 50 grams of fructose.

It’s unclear why some people absorb fructose better than others, but a few things are certain:

  • The higher the amount of fructose, the harder it is to absorb
  • 100% pure fructose (which doesn’t exist in nature) is hardest to absorb.
  • Fructose is easiest to absorb when it’s mixed with an equal or greater amount of glucose.

So why should you care about unabsorbed fructose? Less absorption just means fewer calories, right? Unfortunately, unabsorbed fructose doesn’t exit your system gracefully. On its way out, it stops in your colon, where hungry bacteria have a field day with it. These microbial marauders feverishly ferment the fructose, producing methane, hydrogen, and carbon dioxide gases as by-products. These gases not only make you unpopular at parties, but they can cause tremendous discomfort, bloating, and diarrhea. Delightful.

How do you know if you have fructose malabsorption?

Symptoms: Unabsorbed liquid fructose causes unpleasant symptoms two to three hours after drinking it because that's how long it takes for it to reach the bacteria in your colon and for gases to be generated. If you consume fructose in solid foods or on a full stomach, it may take longer than three hours before you feel discomfort. If you get symptoms within an hour, it’s probably not due to bacterial gases, but rather to osmotic effects (rapid fluid shifts)—fructose can flood the colon with fluid by pulling water out of the surrounding tissues into the gastrointestinal tract, causing sudden diarrhea.

Breath testing: There are tests that can be done at your doctor’s office or using in-home test kits [no link b/c amazon doesn’t sell them anymore] that detect hydrogen and methane gases generated by bacterial fermentation of unabsorbed fructose, but they’re expensive and they’re not perfect. Some people have a positive breath test but no symptoms, and some people with bad symptoms have a negative breath test. There are several possible reasons for these discrepancies:

  • Fructose breath tests use pure liquid fructose (typically 25 grams), which is very hard to absorb, so the test can cause symptoms in people who actually have no trouble with fructose in foods and beverages.
  • Fructose breath tests don’t measure carbon dioxide gases, which can cause bloating and painful stretching of the intestines just like methane and hydrogen can.
  • Fructose breath tests can’t detect osmotic effects.

Fructose and IBS

Although many people associate fructose malabsorption with IBS-D (diarrhea-type), fructose can also cause symptoms of IBS-C (constipation-type) and IBS-M (mixed type). In a recent study, 28% of IBS patients were triggered by 25 grams of liquid fructose (whether they had a positive breath test or not), and their symptoms were all over the map. But do low-fructose diets help reduce symptoms? Yes. In a new study, 56% of IBS patients felt somewhat better on a low-fructose diet and 20% achieved complete relief on a low-fructose diet whether they had a positive breath test or not.

What to do if you suspect you have fructose malabsorption

If you have digestive issues such as diarrhea, gas, bloating, cramping, or even constipation, it's well worth your time to completely cut out fructose for a few days to see if that’s your issue. There are helpful charts below to assist you in figuring out which foods are high in fructose. However, if you find yourself on a deserted island without internet access, keep in mind that fructose is Mother Nature’s sweetener. So here’s a good rule of thumb you can use for all natural whole foods: if it’s sweet, it’s got fructose in it. Conversely, if it’s not sweet, it’s virtually fructose-free. To remove all fructose from your diet, simply remove everything sweet.

How much fructose is OK?

Most people with fructose-related tummy troubles don’t need to completely remove fructose from their diet to feel well. If you take all the fructose out of your diet and your IBS symptoms go away, but you miss sweetness in your life, you could gradually add some back in to figure out how much you can comfortably tolerate. Another option is to use a non-fructose sweetener (see table below). If you have fructose malabsorption but you’d like to include some fructose in your diet, you need to consider both the number of grams of fructose as well as the percentage of fructose to glucose in the foods and beverages you choose. Everyone has a different threshold, but most people can safely eat a few grams of fructose per meal, up to a total of 10 or 15 grams of fructose per day. Since glucose helps with fructose absorption, you want to choose foods that contain at least 50% glucose. I’ve had the tables below designed to show both amount and percentage of fructose to make your choices easier.

fructose malabsorption graph - content of fructose and glucose in foods

To minimize symptoms, you're better off choosing foods from the top half of the tables above because they contain smaller numbers of grams of fructose and at least 50% glucose (to help with absorption). Starchy foods such as grains, beans, flours, and (non-sweet) root vegetables contain little to no fructose and are safe for people with fructose malabsorption. I included one starchy (non-sweet) food (Russet potato) as an example.

fructose malabsorption graph - content of fructose and glucose in sweetenters

As you can see above, most sweeteners contain roughly a 50/50 mix of fructose and glucose, so they may not cause too much trouble, especially if you stick to a teaspoon or less per meal to keep total grams of fructose low. Agave syrup is extremely high in fructose and should be avoided. Brown rice syrup contains no fructose at all, so it is completely safe for people with fructose malabsorption.

fructose malabsorption graph - content of fructose and glucose in beverages

Above you can see that all beverages contain high amounts of fructose, and the majority of them contain more than 50% fructose, so drinking sweet beverages is not a good idea.

Still have IBS symptoms even on a fructose-free diet?

If you remove fructose from your diet and you still have symptoms, you are probably having a hard time digesting something else.

There are plenty of other poorly-digested carbohydrates that can wreak havoc with your system. These include lactose (milk sugar), sugar alcohols (found in fruits and many sugar-free sweets), and many plant starches (such as those in beans and cruciferous vegetables), all of which can cause "IBS" symptoms in susceptible individuals. These types of carbohydrates are affectionately known as FODMAPS, which stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols.

Low FODMAP cookbookSo, if removing fructose doesn’t do the trick for you, I recommend trying a diet that eliminates all poorly-digestible carbohydrates. This approach is the basis for the popular and helpful book The Complete Low-FODMAP Diet by Sue Shepherd PhD and Peter Gibson MD.

Still have IBS symptoms on a low-FODMAP diet?

If you still have symptoms on a low-FODMAP diet, then your problem could be an indigestible protein, or even too much fiber! Please see my post "Common Constipation Culprits" for a list of some surprising foods that can cause major digestive problems for some people.

How about you? Have you sung the IBS blues? What has worked for you? Is fructose your colon culprit or is it something else? Tell your story below so that others can learn from your experience. Know someone else who might find this post helpful? Please consider sharing it!

The next and (truly) final article in this fructose series, "How to Diagnose, Prevent and Treat Insulin Resistance" is about how much sugar is safe for you to eat, how to know if you have insulin resistance, and dietary suggestions that really work to prevent/improve insulin resistance and most common chronic diseases. Included is a downloadable PDF with a list of medical tests for insulin resistance that you can discuss with your healthcare provider and an infographic with tips to improve your insulin sensitivity.

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