Fructose Malabsorption

The old adage “an apple a day keeps the doctor away” is not without merit. Apples are certainly nutrient dense, and consuming them regularly can be a health-enhancing practice—unless you happen to suffer from fructose malabsorption disorder.

For those afflicted with the malady (commonly referred to as fructmal), eating apples, or any food high in fructose, is anything but health enhancing. Here’s a closer look at this surprisingly common but little-known condition.

What is fructose malabsorption?

Fructose is a naturally occurring sugar found in many foods, most notably fruit. In addition, it is used in food manufacturing to sweeten many processed foods and beverages.

In fructmal, a person’s ability to absorb fructose is impaired. Normally, fructose is absorbed in the small intestine, with the aid of a specific protein called GLUT-5. If this protein either is not present or has become inactive, the unabsorbed fructose reaches the large intestine, where it is rapidly fermented by colonic bacteria to acids and gases (predominantly hydrogen, but in some people, methane).

This causes both gastrointestinal symptoms and the proliferation of intestinal bacteria and yeast, which metabolise the fructose. It is important to note that malabsorption is the causative factor in fructmal, not intolerance. People with fructmal have no problem tolerating fructose; their small intestines simply cannot absorb it.

The condition should never be confused with a much more serious genetic disorder called hereditary fructose intolerance (HFI), which can be life-threatening. HFI is usually diagnosed in early childhood and is extremely rare. Fructmal, while unpleasant, is not life threatening.

Fructans

Unfortunately, it isn’t just fructose that can cause problems for fructmal sufferers. Some people with the disorder also have difficulty absorbing fructans.

Fructans are chains of fructose molecules that end in a glucose molecule. Fructans are found in several grains and vegetables, including wheat, rye, onions, artichokes, asparagus, beans, zucchini, coconut milk and tomato paste.

The prebiotics inulin, chicory and fructo-oligosaccharides (FOS) also contain fructans. In addition, sugar alcohols such as sorbitol, xylitol and maltitol can also exacerbate the condition. Sorbitol occurs naturally in stone fruits, apples, pears and dried fruits, and it is also used as a sweetener in sugar-free lollies and chewing gum.

Symptoms

The symptoms of fructmal are mainly digestive—abdominal pain and gas, bloating, nausea, acid reflux, diarrhoea and constipation.

However, depending on the severity of their condition, it is not uncommon for victims of fructmal to also experience depression. Although this may seem strange or severe, it’s not—when fructose makes it to the large intestine it degrades tryptophan, an essential amino acid the body requires to make serotonin (a mood regulator).

Not surprisingly, studies indicate that fructose malabsorbers do indeed have lower tryptophan levels than normal controls. They also have reduced serum zinc and folic acid levels, which may increase the risk of depression. The severity of symptoms varies greatly among fructose malabsorbers—some people seem to be able to consume small doses of fructose without problems while others are symptomatic after ingesting even minuscule amounts of the sugar.

Causes

A definitive cause for fructose malabsorption has not yet been established, but several contributing factors have been postulated. They include

• overuse of high fructose foods (especially those sweetened by high fructose corn syrup)
• bacterial abnormalities in the gut
• inflammation
• stress

The prevalence of the disorder is quite high. It is estimated that 30 per cent of people in the Western Hemisphere may have some degree of fructose malabsorption.

Diagnosis

You cannot be certain you have fructose malabsorption disorder until you have been diagnosed by a health care practitioner. Fructmal mimics many other gastrointestinal disorders, including IBS and gluten intolerance, so it is crucial to get a definitive diagnosis.

Incomplete fructose absorption is detected by breath testing for hydrogen (or methane) production after consumption of a fructose-containing beverage or food. Generally, a dose of fructose is administered after a fasting period of eight to 12 hours (during which patients do not consume carbohydrates). Breath hydrogen levels are then measured at specified intervals for a few hours. The body does not produce hydrogen by itself, so presence of the gas indicates malabsorption of fructose.

Treatment

The treatment or management of fructmal may seem fairly obvious—simply eliminate fructose-containing foods from the diet. In truth, treatment is neither that simple nor, thankfully, that severe. Not every food that contains fructose is a problem for people with fructmal. It is important to understand how fructose occurs in foods to know which foods are problematic for fructose malabsorbers.

Fructose naturally occurs with other sugars, like glucose, in foods. The good news is that glucose aids the absorption of fructose—it acts as a carrier molecule for fructose, piggybacking it into the wall of the small intestine where it is readily absorbed. That means fruits such as strawberries, which contain approximately equal amounts of fructose and glucose, may be eaten by malabsorbers without any nasty consequences.

It also means they may be able to tolerate certain high fructose foods on occasion if they combine them with a high glucose food (such as dextrose)—for example, apple sauce “sweetened” with dextrose powder. This only works if the levels of glucose are as high, if not higher, than the levels of fructose, so keep in mind that you can end up consuming a lot more sugar than is ideal by employing this strategy too often. And unfortunately, it only works with free fructose, not fructans.

In general, it is best to simply avoid foods high in fructose, fructans, sugar alcohols and foods with inulin, chicory and FOS added to them as “prebiotics”. Studies concur that following a fructose-restricted or -reduced diet does indeed bring about a marked improvement in symptoms.

Tips

• Use dextrose powder to sweeten plain yoghurt, muffins, other baked goods and the occasional high fructose treat.
• Allow bananas to ripen completely to increase their glucose content.
• Try eliminating fructose for two weeks, then reintroduce it to determine your own threshold.
• Foods that may be better tolerated by those with fructmal include carrots, corn, potatoes, grapefruit, radishes and spinach.
• Natural sweeteners that may be better tolerated by those with fructmal include brown sugar, raw sugar, molasses and maple syrup.
• When consuming fructose, it may be better to do so on a full stomach, after meals.

Foods to avoid or reduce

Foods to be wary of include

• sweeteners such as high fructose corn syrup, honey and agave
• fruits such as apples, dates, figs, grapes, pears, prunes, melon, watermelon, mango, quince, raisins and cherries
• all dried and canned fruits
• stone fruits that contain sorbitol, such as plums, peaches, nectarines and apricots
• sugar-free chewing gum and lollies sweetened with sorbitol or other sugar alcohols
• fructans such as rye, wheat, spelt, coconut cream and milk, tomato paste, artichokes, onions, asparagus, inulin, chicory and FOS

Seek out supplements

Since many fruits, vegetables and grains that contain fructose and fructans are very healthy, people with fructmal may be missing out on key nutrients if they avoid these foods. A health care practitioner may be able to recommend supplements that can fill any gaps in the fructmal sufferer’s diet.