The key to tackling bad breath may start with your gut

Bad breath can undermine confidence, but rather than munching on mints, supporting your gut microbiome, maintaining good oral hygiene or talking to your doctor could tackle the problem at its source 

Side view close-up of a woman smelling her breath with hand near mouth, studio shot on a white background. Feelgood

If people are quick to bring out the mints when you’re in the vicinity, or recoil when you start speaking, you may be suffering from halitosis.

For non-medical practitioners, this means smelly breath, and it’s far more common than you might expect. According to the Irish Dental Association, persistent bad breath afflicts as many as 25% of the Irish population.

While poor oral hygiene and underlying gum disease account for the majority of cases of halitosis, for somewhere between 10% and 15% of cases, there may be a different explanation.

“There can be gastrointestinal or respiratory causes, or it could be due to systemic diseases like liver disease, renal failure, diabetes, and other rarer conditions,” says Aonghus Lavelle, a professor and microbiome researcher at University College Cork.

Microbiome experts have become increasingly interested in the bidirectional link between the oral cavity and gut, with the gastrointestinal (GI) tract effectively serving as one long tube which connects the mouth with your intestines.

As a result, severe constipation has been suggested as a potential contributor to bad breath. The theory is that gases created in the gut may be absorbed into the bloodstream and later exhaled through the breath.

Fungi in the intestines

But it isn’t just constipation. Other cases of gut-related bad breath are thought to originate as a result of a condition known as small intestinal bacterial overgrowth or SIBO. While the intestines are well known for housing the gut microbiome — the vast colony of bacteria, viruses and fungi which reside in our intestines — most of this microbiome is located in the large intestine or colon.

SIBO occurs when bacteria start congregating in the small intestine in unusually high densities, where they break down food and produce sulphurous gases which enter the bloodstream.

“Then, when we breathe out, they can give our breath a bad smell,” says Lavelle.

In some particularly extreme cases, certain species of bacteria which have been linked to SIBO can turn sugars and proteins in the small intestine into particularly noxious chemicals such as butyric acid, which has an odour resembling vomit, or amines which smell of rotting flesh.

So how do you know if you have SIBO? The condition is most typically characterised by symptoms like abdominal pain, cramping, bloating, and diarrhoea. People taking antacid medications like proton pump inhibitors for heartburn, acid reflux and indigestion are also known to be more vulnerable to SIBO because the drugs block acid in the stomach, which would otherwise kill microbes, enabling more bacteria to colonise the small intestine.

Crohn’s or coeliac disease

In some cases, the problems are not necessarily caused by an overgrowth of bacteria, but chronic health conditions which cause food to linger in parts of the GI tract.

Lavelle likens healthy digestion to a continuous river of food particles flowing through the small intestine. However, digestive conditions such as Crohn’s disease and coeliac disease make it harder for people to break down their food, sometimes leading to more undigested food particles gathering in the small intestine.

Likewise, for people suffering from gastroesophageal reflux disease, where the stomach’s valves weaken, food can end up seeping out of the stomach back into the oesophagus.

In both cases, this can lead to pungent gases being released from the partially digested food, which can reach the breath.

“Anytime you get a bit of [food] stagnation in your small intestine, that’s where you can get issues, Sometimes patients who’ve had surgery on their gastrointestinal tract can also be more at risk of this.”

So what can you do? SIBO can sometimes be treated with antibiotics, but Lavelle says that there’s a range of approaches that can be used. These can include diets that focus more on foods which contain less fermentable carbohydrates, for example, more carrots, spinach, cucumber and tomatoes, and fewer fruits like apples, pears, and cherries. The idea is to put foods into the body which are not as easy for bacteria to grow on.

Lavelle says that it can involve trial and error. “Sometimes the approach is to use prokinetics or motility agents, medicines that speed up transit, so trying to push stuff through the gastrointestinal tract a little bit quicker,” he explains. “Occasionally, we’ll treat with antibiotics, and then we’ll look at you know trials of different diets that might help.”

At the same time, Lavelle is keen to emphasise that such gastrointestinal causes represent a minority of cases of halitosis. If someone has bad breath, it shouldn’t immediately be assumed that the culprit lies in their gut, even if they have digestive conditions. “Patients with established gastrointestinal disease don’t typically complain of bad breath, other than sometimes with reflux or SIBO,” he says.

Instead, people with halitosis are most likely to have issues relating to oral hygiene and underlying gum disease or periodontitis. Both Lavelle and Danielle Colbert, principal dentist at The Fresh Breath Clinic in Dublin, say that this should be investigated first before considering other possible causes.

“The common oral cause is that people have accumulated a lot of pathogenic bacteria, which have formed plaques underneath the gums,” says Colbert.

To avoid this, the main advice is simply not to skip regular check-ups to prevent plaque from accumulating, as well as daily flossing, to ensure that potential problems can be nipped in the bud. “The World Health Organization recommendation for the last 50 years has been to go to your dentist every six months,” says Colbert.

“And if you need a cleaning, you can get that done with a hygienist.”