Would you believe that there’s yet another type of condition to consider if you are troubled by such common gastrointestinal (GI) symptoms as bloating, flatulence and the like? This one has to do with something contained in foods that are supposed to be excellent for our health -- fruit!
This is a fairly big deal -- it affects about one-third of the population, many of whom have no idea that this problem even exists. If you suffer frequent digestive distress and aren’t sure why, this is a story that you really want to read closely.
The problem is called fructose malabsorption.
How Bad Is It?
The problem we’re talking about is fructose malabsorption, not fructose intolerance, which is what many people mistakenly call their affliction. These are separate issues according to Dr. Lustig, a pediatric gastroenterologist at the Mary Bridge Children’s Hospital & Health Center in Tacoma, Washington.
The difference: Intolerance is a hereditary, lifelong condition present at birth that makes people unable to tolerate any fructose whatsoever. It is incurable and occasionally fatal, but fortunately it is also very rare. Conversely, the symptoms of fructose malabsorption generally range from mild to moderate, and Dr. Lustig said that the problem can develop at any time in life.
Fructose malabsorption often is misdiagnosed (when it is diagnosed at all) as lactose intolerance because the symptoms of both are strikingly similar -- and, in fact, it is not unusual to have both conditions. It also affects 30% of people with irritable bowel syndrome (IBS).
Where’s the Fructose?
Fructose is everywhere. It is a natural sugar found in virtually all fruits, and its equally problematic molecular cousin fructan, a starch, can be found in a few vegetables. Man-made products containing fructose are common, the best known example being the sweetener high-fructose corn syrup. Fructan is used in diet sweeteners in the form of inulin, maltitol and sorbitol.
Despite the ubiquity of fructose, the human body isn’t designed to handle large amounts of it. It is the small intestine’s job to absorb fructose, but excessive amounts can be overwhelming even for people who don’t have problems with malabsorption. If fructose is not absorbed properly, it gets passed from the small intestine into the large one. Once there, colonic bacteria metabolize the fructose, producing abnormally high levels of hydrogen and methane as well as fructose fermentation -- this, in turn, is what causes GI distress.
Anyone can suffer discomfort from eating lots of fructose in one sitting (say, 50 grams -- what’s in about two and one-half medium-sized apples), but in people with fructose malabsorption this threshold is about 25 grams, according to Dr. Lustig. Many people with this condition can’t even handle that much without becoming uncomfortable.
If the symptoms described above sound familiar to you and you suspect that you suffer from fructose malabsorption, here is how you can get control of the problem.
To understand why fructose in some fruits is more problematic than it is in others gets a little tricky, so bear with me. Along with fructose, fruits generally contain glucose, another type of natural sugar (it’s what is in sucrose, which is plain old table sugar). The presence of glucose in a food enhances absorption of its fructose, and so when you eat fruit with a high glucose-to-fructose ratio -- ripe bananas, for example -- you are unlikely to experience those unpleasant symptoms. On the other hand, if a person with fructose malabsorption eats more than a small quantity of fruits with more fructose than glucose -- apples and pears are good examples -- GI discomfort often follows. What to do...
- Get a proper diagnosis. A gastroenterologist will first eliminate serious digestive disease such Crohn’s, ulcerative colitis or H. pylori, and after that give you a breath hydrogen test (it’s simple, and just involves blowing into a special instrument). This may reveal abnormal levels of colonic hydrogen and carbon dioxide and tell whether the cause is fructose malabsorption or lactose intolerance or both. Dr. Lustig says the breath hydrogen test also reveals whether a small-bowel bacterial overgrowth is present, a condition that often coincides with fructose malabsorption and can be treated with a course of antibiotics.
- Eat foods with more sucrose than fructose.
- Stone fruit -- apricots, nectarines, peaches, plums.
- Berries -- blackberries... blueberries... boysenberries... cranberries ... raspberries... strawberries.
- Citrus fruits -- grapefruits... lemons... limes... mandarins... oranges (but not citrus juice, because it lacks the fiber)... tangerines... kumquats.
- Others -- ripe bananas... kiwi... passion fruit... pineapple... surprisingly, rhubarb, which has a good balance of naturally occurring sugars.
- Table sugar -- but in moderation, because table sugar (the main source of sucrose) also contains fructose.
- Limit or avoid foods that are higher in fructose than sucrose. This list includes ...
- High-fructose corn syrup, because most (though not all) forms of it include more fructose than sucrose.
- Fruit juice concentrates.
- Agave nectar and syrup.
- Watermelon... honeydew melon... mango... guava and papaya... star fruit... apples... pears.
- All dried fruits.
- Fortified wines (sherry, port).
- Limit foods containing fructan (a carbohydrate polymer of fructose).
- These include asparagus... Jerusalem artichokes... leeks... onions... garlic ... wheat. (Researchers are investigating how cooking might tame fructans, especially in garlic and onions.)
- Fine-tune your diet by finding which foods and how much fructose/fructan you can comfortably consume. Ideally you should map this out with a dietician trained in working with patients with fructose malabsorption, says Dr. Lustig, especially if your symptoms are frequent. However, if your symptoms are relatively mild, you may be able to manage your problems by keeping notes to see which fructose/fructan foods you can comfortably eat and which ones cause problems. For example, many people find that any amount of dried fruit brings on GI distress while a limited amount of fresh fruits daily is just fine. Don’t overlook wheat-containing foods in your investigation -- besides the fact that wheat contains fructans, it may be that fructose malabsorption is something you should check out if you have "gluten sensitivity."