"Stealth fiber" increasingly added to processed foods, while not a problem for most, can cause gastrointestinal discomfort for some who may not know they're consuming too much of it, Minnesota researchers warn. The fiber is called "inulin."
"Normal fiber foods like wheat bran and legumes are self-limiting; it's hard to over-eat them," Joanne Slavin, a registered dietitian in the department of food science and nutrition at the University of Minnesota at St. Paul, told Reuters Health.
Inulin, she explained, may be in chocolate bars, drinks, and snacks around the house, and "before you know it, you may eat more than you can tolerate and have gastrointestinal issues you wouldn't necessarily associate" with those foods.
Inulin is a carbohydrate fiber that occurs naturally in many foods like bananas, wheat, onions, and garlic. Found in high concentrations in chicory root, is can be extracted for industrial use. Unlike more familiar carbohydrates, which are broken down in the small intestines and turned into fuel for the body, inulin passes through the small intestines to the colon where it stimulates the growth of "good bacteria" and is fermented by bacteria. In some people it can cause gas, bloating, flatulence, and diarrhea.
Because of its growing popularity as a food additive, Slavin and her colleagues wanted to assess how much inulin it takes to cause gastrointestinal problems.
They designed a study involving 26 healthy men and women aged 18 to 60. After a night of fasting, once a week for five weeks, participants were fed a breakfast of a bagel with cream cheese and orange juice. The orange juice was mixed with a placebo or with 5- or 10-gram doses of two commonly used inulin products — native inulin and shorter-chain oligofructose.
After their "fiber challenge," participants were called several times over two days and asked about symptoms such as gas/bloating, nausea, flatulence, stomach cramping, diarrhea, constipation, and GI rumbling.
Those that got any dose of inulin generally reported "mild symptoms;" the highest scores in every symptom except constipation were reported by those who got 10 grams of oligofructose. The findings are in line with previous research that found the short-chain "sweet" inulin causes faster fermentation in the gut leading to more gas and gastrointestinal symptoms.
Flatulence was the most common symptom reported by all subjects who got fiber although symptoms were "highly variable" among individuals and many subjects did not experience any, the investigators say.
Slavin and colleagues conclude, based on their study, that most healthy people can tolerate up to 10 grams of native inulin and 5 grams of the "sweet" inulin a day.
Food manufacturers, faced with demands to reduce calories, fat, and sodium while increasing fiber and flavor, are increasingly turning to products like inulin. They have discovered they can chemically manipulate the chemical structure of inulin to mimic tastes and textures consumers want in food. "It's like a food manufacturer's nirvana," Slavin said.
Inulin can be found in high-fiber breakfast bars, ice creams, and beverages among other processed foods. The label may list inulin, chicory root extract, oligosaccharide, or oligofructose. For example, the Fiber One Chewy Bar with 9 grams of dietary fiber lists chicory root extract as its top ingredient.
Slavin and her colleagues urge continued study of tolerance levels of food additives like inulin because their use is likely to continue to grow and "there is the potential for overuse."
The research was funded by Cargill, a maker of inulin food additives, which provided the product used in the study.
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