Welcome to Gut Check, our column dedicated to the complex, ever-evolving relationship between food and our bodies. Whether you’re curious about mindful eating or want to understand what makes picky eaters picky, read on and let award-winning journalist Betsy Andrews answer all your burning questions. 

My childhood halitosis, which went away soon enough, might have been related to my braces—a cumbersome, mid-1970s rack. For most, the cause of bad breath is gum disease or an accumulation of bad bacteria in the mouth. Even so, I’ve long wondered if mine could have come from deeper in my body. Starting around age 10, I had a recurrent kidney infection. As it turns out, a malfunctioning kidney can release a smelly compound called dimethyl sulfide into the blood that in turn gets excreted into your breath.

Thinking back to my bout of stink mouth got me considering all the reasons someone might wind up with chronic bad breath, and what they can do about it. Halitosis—a mashup of Latin “halitus,” or breath, and the Greek suffix “-osis,” meaning disease—is a descriptive term for an understudied condition. Dr. Dan Baumgardt, a general practitioner and lecturer at the University of Bristol, notes myriad causes: a buildup of crystals in the salivary glands, tonsil stones from food debris, advanced diabetes, sinusitis, reflux, and on and on. 

Reflux—stomach acid washing back up into the esophagus—is a common digestive issue. I often write about the gut microbiome, so I got curious—could the gut be a culprit? The experts I spoke with didn’t agree on everything, but they concurred that halitosis signals that something in the body is off. Beyond its social ramifications, persistent bad breath “can be a real telltale,” Baumgardt says. So instead of hiding behind breath mints and hurt feelings when people around you cry “Foul!” seek expert help and get to the root of the problem. 

An allopathic (conventional Western medicine) practitioner at Manhattan Gastroenterology, Dr. Mikhail Yakubov has met his share of halitosis sufferers—and their suffering partners. “It’s always the same. A guy walks in: ‘My wife is angry. My breath smells.’ I’m usually the third or fourth doctor they’ve seen, and everyone tells them nothing is wrong,” he says. But with his traditional medical training, Yakubov usually tells them, “It’s not a GI issue. You’re in the wrong place.” 

Traditional gastroenterology does recognize some causes of halitosis, and they’re pretty hardcore. One is a bezoar, a mass of indigestible material in the GI tract, such as plant fibers, seeds, pits, hair, or another inedible swallowed object. “It binds with food, creates a ball, and gets stuck,” Yakubov explains. As the food rots, it can release foul odors upward. As horrifying as that sounds, bezoars are thankfully rare—at least in those of us old enough to not to put Legos in our mouths. (Believe it or not, one treatment involves dissolving the mass with Coca-Cola.) 

A more prevalent gut-related source of rancid breath, especially in men over 60, is Zenker’s diverticulum, a pouch that forms in the esophageal lining. Instead of moving to the stomach, food gets trapped there, putrefying and giving off icky odors. Endoscopic surgery usually does the trick to fix it.

Beyond these rare instances, Yakubov doesn’t believe the gut is implicated in most cases of halitosis, even if he admits that “this is one case where traditional medicine doesn’t help people” very much. So he sends patients elsewhere—usually to a periodontist.

Yakubov often refers patients to Dr. Scott Froum, a periodontist and the scientific director and cofounder of Meraki, an integrative wellness clinic in New York. A naturopath focusing on anti-aging, his attention is often drawn to patients’ gut health. “If you control the gut, a lot of things get better”—including bad breath. “I was seeing halitosis in patients who have good oral hygiene,” he says. It didn’t make sense until he took blood, stool, and urine samples and “the tests just lit up with digestive problems.” He explains that halitosis is too often dismissed as cosmetic, when in reality, it’s metabolic. It’s sometimes “a canary in the coal mine that can lead to bigger problems down the road.”.

What Froum often winds up treating is inflammation. Inflammation disrupts the gut’s fungal community—or mycobiome—often leading to overproduction of smelly candida. It can also cause dysbiosis, a gut microbiome imbalance that gives off its own putrid, volatile compounds. Emerging research, in fact, connects small intestinal bacterial overgrowth to halitosis. Froum’s treatment hinges on the 5R Protocol: Remove inflammation triggers, replace them with digestion-enhancing supplements, reinoculate the gut with prebiotics and probiotics (such as fermented foods), repair the gut lining with additional supplements, and rebalance the whole system through stress reduction, exercise, and good sleep hygiene. There’s just one catch: Stop doing any of these, and the halitosis could come back. 

You probably don’t need a specialist to tell you that certain foods and drinks can spoil your breath—but what’s surprising is why. Sugar, for one, is odorless, but oral bacteria thrive on sugary foods, notes Top Nutrition Coaching’s Lena Bakovic, a registered dietitian nutritionist. That’s why overdoing it on cakes and candy can rot your teeth and gums, resulting in a stinky mouth. Eating a balanced, mostly plant-based diet is the way to go: Nitrate-rich beets and leafy greens have proven better at battling gum disease than certain mouthwashes. 

For diabetics battling halitosis, the problem might be unregulated blood sugar. Without enough insulin to help the body process glucose for energy, blood sugar spikes and the liver starts producing ketones—fat-derived compounds the body uses as an alternative fuel source. This process, called ketoacidosis, can cause a sickly sweet odor on the breath, but if that’s the case, it’s the least of your concerns: Ketoacidosis is a life-threatening emergency.  

There’s another, less dangerous reason the liver might pump out ketones: ketosis. It happens during fasting or low-carb, high-fat diets, when the body runs out of glucose and turns to fat for energy. Acetone, one of the ketones, “diffuses across the lungs and produces a sweet, solvent-like smell that can be perceived as bad breath,” explains FullWell founder and registered dietitian Ayla Barmmer. The result? Rapid weight loss—paired with breath that smells like nail polish remover. 

Among medical causes of halitosis, acid reflux is one of the more manageable. According to Maude Morin, a registered dietitian with Canada’s JM Nutrition, those with the condition should steer clear of high-fat or acidic foods, avoid reclining after meals, wear loose clothes, and drink plenty of water to clean the mouth. As the reflux subsides, she says, so does the bitter or acidic odor it engendered.

Dieticians agree: A low-carb diet centered on fiber-rich veggies and polyphenol-rich fruits helps ensure a clean-smelling mouth—even if some of those are breath-strafing alliums. Garlic and onions, especially when raw, can cause what pros call “transient halitosis.” You might smell pungent for a day, but it’s temporary and harmless. One study showed that raw apple, lettuce, or mint can help neutralize the odor.  

Beyond fruits and veggies, fermented foods may help combat bad breath. “Kimchi, yogurt, and kefir can not only positively influence overall health, but also contribute to reducing halitosis,” Bakovic says. Studies back her up.

When it comes to beverages, the biggest villain is booze—at least while your body is processing it. Most gets processed in the liver and peed out, but some escapes through your mouth, causing that familiar alcohol funk. Once the alcohol clears, your breath returns to normal, though prolonged daily drinking can contribute to odor-inducing periodontitis. 

Alcohol also causes dehydration, which concentrates volatile sulfur compounds that mess with your breath. For both drinkers and non-drinkers, Barmmer suggests staying well-hydrated with fluids infused with mineral-rich parsley, chlorophyll, or green tea. These contain catechins that bind with sulfur compounds while your body rehydrates. 

The solution really might be as simple as drinking more water: A dry mouth is a breeding ground for bad bacteria, Bakovic explains. Water gets your saliva going, which flushes out bacteria. Stuck at a friend’s without a toothbrush? That’s not great oral hygiene, but in a pinch, rinsing with water has been shown to lessen morning breath. 

I’ll never know for sure what caused my smelly mouth back in middle school, but now—as someone who hydrates, brushes, and flosses assiduously—I’m fairly confident it won’t return. If it does, I’ll head to my periodontist. And if that doesn’t help, I’ll look to my gut and clean up my diet. After all, fresh breath is just one more reason to eat your veggies.