But most of us overlook a growing source of the problem: inulin, or chicory root extract, one of the most popular ingredients in “high-fiber” foods.
“Of all the fibers added to foods, inulin is the one that probably causes the most intestinal gas,” says fiber expert Joanne Slavin, professor of nutrition at the University of Minnesota. “Inulin contains sugars that our digestive enzymes can’t break down.”
The enzymes do just fine with sugars that have only one or two basic units (called saccharides). Sucrose, or table sugar, for example, is a disaccharide that is broken down in the small intestine into fructose and glucose.
But when it comes to sugars made up of three or more units—often called oligosaccharides—our enzymes are useless. So the sugars end up as food for the bacteria in the gut.
“Inulin is quickly and completely fermented in the large intestine,” explains Slavin. And when your bacteria finish fermenting it, you get stuck with the gas they give off.
Why do beans cause gas?
“Beans are notorious for causing gas because they have sugars like raffinose and stachyose,” notes Slavin. Raffinose has three sugar units. Stachyose has four.
“If you look at the literature on treating or cooking beans to make them less gassy, it’s mostly to get the oligosaccharides out of there,” she adds.
(Beano tablets can prevent gas because they contain an enzyme that breaks down raffinose and stachyose.)
Whether inulin is a problem depends on how much you eat and who you are.
“Our review of studies found that inulin is generally well tolerated at levels up to 15 grams a day,” says Slavin. But at around 20 grams, flatulence or bloating is more likely. “So dose is a big issue, and there’s also individual variability.”
Most Fiber One Chewy Bars have nine grams of fiber per bar, and much of it comes from chicory root extract (inulin).
“If you have a serving of beans, you’ll get about three grams of oligosaccharides, not nine grams,” says Slavin. “And they’re more manageable in a real food because they’re digested more slowly and usually mixed with other foods.”
“They’re low-calorie carbohydrates because they’re not completely digested and absorbed,” explains Slavin. “Typically, if you’re eating sugar-free candy or gum, your exposure to sugar alcohols is low, but if people eat the whole bag of candy, it can cause gas.”
Sugar alcohols aren’t all equal, though. In small studies, some people complain of gas when doses of sorbitol reach 10 to 20 grams, but few complain unless they get at least 30 to 40 grams of maltitol.
Most foods don’t have that much. Breyers CarbSmart ice creams, for example, have five grams of sorbitol per half cup, but many people start at a whole cup. Breyers No Sugar Added ice creams have six to eight grams of maltitol per half cup. And Baskin Robbins No Sugar Added Caramel Turtle Truffle ice cream has 24 grams of maltitol per half-cup scoop.
Of course, some people may eat more than one food with sugar alcohols during the course of a day. And people vary. So if you are wondering what foods cause gas for you, remember that “most people can tolerate normal doses, but not everybody is the same,” says Slavin.
On the plus side, sugar alcohols have fewer calories than sugar, and inulin spurs the growth of Bifido bacteria, which may be good for gut health (that’s why it’s called a “prebiotic”). But the more bacteria in your gut, the more gas they give off.
“Scientists argue that gas isn’t bad for you, but most people say it’s not acceptable,” says Slavin. “If you have gas, you should definitely consider what you’re eating. If it’s a lot of fermentable fiber or sugar alcohols, that could be the explanation.”
Sources: Crit. Rev. Food Sci. Nutr. 49: 327, 2009. Am. J. Clin. Nutr. 68: 357, 1998.
This post was originally published in 2013 and is updated regularly.