Even if you skip the onions on your burger, your breath still might stink after your meal: Eating fast food may give you dragon breath, new research from Korea found.

In the study, young people who ate fast food most frequently—at least three times per week—were 15 percent more likely to report having bad breath, or halitosis, than those who ate that kind of food least often.

That’s because those burgers and fries contain an ample amount of greasy residue—there’s a reason they come with so many napkins—that can cause a smelly chain reaction inside your body, which you spew back up through your mouth, says Tripti Meysman, D.D.S., founder of the Minneapolis-based CityTooth dentistry practice.

“The oils interact with your digestive enzymes, and that can cause bad breath,” she says.

The grease in fast food also increases acidity in your gut, which may lead to gastric reflux—another contributor to bad breath, Dr. Meysman says.

What’s more, if you have an underlying systemic condition like diabetes, the smell can be worse. The bacteria in your mouth feed on sugar, and higher levels of it associated with diabetes give them plenty to feed on, allowing them to multiply more easily.

That’s likely why the study also found that people who ate the highest amount of sugary foods—think regular snacks of candy or soda—were 19 percent more likely to have halitosis than those who ate the least.

While the study included only young people, the effects from these kinds of food can affect your breath at any age, says Dr. Meysman. In fact, you may be more prone to halitosis in general as you get older, due to reduced saliva secretion, medication side effects and kidney and liver issues.

If you want to keep your mouth smelling fresh, that can start with your diet, too. According to the study, people who ate the most fruits and the most vegetables had a significantly reduced risk of bad breath.

Still, if bad breath sneaks up on you despite a healthy, produce-rich diet, your best bet is to brush the smelly bacteria off your teeth and tongue as soon as you can, Dr. Meysman says.

But if that’s not an option, your snack can work in a pinch. Eating an apple can freshen your mouth because they contain compound that have been linked to inhibiting the activity of bacteria in your mouth.

Oranges or strawberries work as well because their vitamin C creates an acidic environment in the mouth that can make it tough for bacteria to thrive.

And of course, it helps to maintain proper oral hygiene—and dental cleanings every 6 to 12 months—to reduce halitosis risk no matter what you eat, Dr. Meysman says.