Why Do Healthy Foods Give Me Gas?
In my household, for reasons that are obscure even to me, “fart” is a bad word. At some point, my wife and I must have decided that we didn’t want to hear our kids use the F-word all the time, so we adopted “toot” as a gentler substitute. Beans and other legumes are often on our menu, and things can get pretty tooty around here.
The medical term for gas is “flatus.” While gas production varies from person to person, research has found that healthy people “pass flatus” up to 25 times a day. According to a 2013 study in BMJ, a lot of plant-based foods — legumes in particular, but also whole grains, some fruits, and many vegetables — are common gas triggers. To find out why this is so, I spoke with Robert Lustig, MD, a digestive health researcher and emeritus professor at the University of California, San Francisco.
Lustig says it all comes down to the microbes that populate the human gut. These bacteria number in the billions and play an indispensable role in health and digestion. “Your gut is just a bag of bacteria, and they eat what you eat,” he says.
Fiber is a part of plant foods that the gut can’t break down and absorb. It passes basically intact through the GI tract — improving the healthy flow and absorption of other food molecules — until it reaches the colon, which is where the bulk of the gut’s bacteria live. Some of these bacteria feed on fiber, and one of the byproducts of this feeding is gas, Lustig explains.
While the gas is unfortunate, bacteria that break down fiber also produce a number of metabolites, including short-chain fatty acids (SCFA), which reduce gut inflammation and do other good work for us. Butyrate, for example, is an SCFA that supports the health of the epithelial cells that form the gut’s protective lining, Lustig says. Fiber is also considered a prebiotic because it encourages the proliferation of healthy gut bacteria.
Despite all these benefits, some people purposely avoid fiber-rich foods — especially legumes — in order to dodge gas. This is a problem. According to nutrition resources from the University of California, San Francisco, the average American gets only about 15 grams of fiber each day, while national diet guidelines encourage intakes in the range of 25 to 30 grams. Some experts have speculated that fiber-deficient diets may be contributing to the rise of inflammatory bowel disease and could also be a factor in Type 2 diabetes and other metabolic conditions.
It’s important to note that, for people who have digestive health issues, beans and other fibrous plant foods can in some cases exacerbate gut symptoms. For those people, eating more of these foods can cause trouble. But for everyone else, gas itself isn’t a health risk — though it may be an indicator that our diets and guts are a little out of whack.
“Over the last 75 years, there’s been a progressive change in our diets where we’re taking out more and more of these complex carbohydrates and replacing them with processed foods,” says Emeran Mayer, MD, a gastroenterologist at UCLA and author of the forthcoming book The Gut-Immune Connection. “Since we’ve grown up on a diet that’s deficient in these complex carbohydrates, it’s quite possible that we react to these foods with increased gas production because of a lack of abundance of certain microbes.”
The good news, Mayer says, is that eating more plant foods should help shift your gut’s population of microbes in ways that will eventually reduce your gas production. “If you’re an omnivore, and all of a sudden you switch to a vegan diet, it’s quite likely that initially you will develop a lot of gas and bloating, but for the most part that will improve as you eat more of these foods,” he says. “I recommend that people make changes gradually.”
Gas can be embarrassing. But a little extra tooting shouldn’t dissuade anyone from eating more healthy foods.