The problem with halitosis, aka bad breath, is that it is devious. You can have it and not know it. It is difficult to smell your own breath and the people you encounter in your daily activities may be too kind or embarrassed to alert you to the problem. Halitosis can also be challenging to eradicate. Many factors can increase the likelihood of unpleasant breath including periodontal disease (disease of the gums and bones that support the teeth), dry mouth, smoking, alcohol consumption, dietary habits, obesity, dehydration, starvation, high physical exertion, advanced age, certain medications and poor dental care (1). Fortunately, the vast majority of breath odour problems are within your own power of control.
Causes of Halitosis
Though there are a variety of conditions that play into the creation of disagreeable breath, in 80 to 90 % of halitosis cases the source can be found within the mouth itself. The major contributors by far are potent molecules derived from foods called volatile sulfur compounds (VSCs). VSCs are chemicals that give some foods their specific flavours and odours and they can be detected by smell or taste at very low concentrations. VSCs can be specifically identified and their intensity measured in the breath with the help of a specialized meter. The high sulfur-containing amino acids, methionine and cysteine, found mainly in proteins from red meat, poultry, cheese and other animal-derived foods, are the most common origins of VSCs. The most important VSCs for bad breath are hydrogen sulfide, dimethyl sulfide, dimethyl disulfide, and methyl mercaptan (2,3,4,5,6).
Bacteria living in the mouth are the agents that actually create the odours that end up as bad breath. These microorganisms perform the necessary step of degrading sulfur-containing amino acids into foul-smelling VSCs. VSC-producing bacteria are anaerobic, meaning that they don’t require oxygen for growth, and the fissured irregular surface of the upper back third of the tongue appears to be the favourite place for these bacteria to thrive. This area can contain as much as four times more bacteria than any other part of the mouth (1,2,4,5,7).
VSCs are the culprits behind “morning breath”. Saliva in the mouth acts as a cleaning agent, keeping bacteria at manageable levels. During sleep, saliva production decreases and self-cleaning of the mouth is inadequate, allowing an upsurge in VSC-producing bacteria and the development of offensive breath upon awakening (8).
Some foods simply have a distasteful smell. One case in point is the allium family of vegetables. These include garlic, onions, shallots, leaks and scallions and they can be another source of bad breath, especially when they are eaten raw. Residues of these vegetables caught in the teeth emit their unpleasant odour as long as they remain in the mouth and, after the digestive system breaks down swallowed alliums, some of the components released are quite odorous. Once absorbed into the bloodstream, these bitter constituents can make their way into other parts of the body to be breathed out by the lungs or emitted from pores. Halitosis caused by ingesting alliums is temporary (19).
The remaining 10 to 20% of halitosis cases originate from more serious circumstances such as a poorly functioning stomach or pancreas; liver or kidney failure; or respiratory tract infections. Certain medications reduce the flow of saliva which can also cause unpleasant breath odour (2,8).
Halitosis affects both healthy people and those with periodontal disease, a gum condition that can be mild (gingivitis) or advanced inflammation of the gums with destruction of bone surrounding the teeth (periodontitis). Occasional bouts of bad breath usually stem from food ingestion while longstanding halitosis almost always reflects back to periodontal disease (10). Interestingly, periodontal disease can be a source of objectionable breath but, more importantly, VSCs and the bacteria that produce them are instigators of chronic inflammation and periodontal disease. VSCs are also toxic to human cells, even at low concentrations and the VSCs hydrogen sulfide and acetaldehyde are associated with oral and digestive tract cancers (1,9).
How Does Food Affect Breath Odour?
A 2008 study out of Germany enrolled its participants in a nutritional intervention programme under the direction of nutritionists. All subjects were suffering from untreated mild or moderate chronic periodontitis. They were transitioned into a diet upgrade which was based on “wholesome nutrition”, eating mostly foods of plant origin that had been processed as little as possible. Fat was limited. The diet consisted mainly of vegetables, fruits, whole-grains, potatoes, legumes and dairy products. Consumption of meat, fish and eggs was limited to one to two portions a week. After a year, participants showed significant reductions in gum inflammation and decreased concentrations of inflammatory cytokines in the mouth, both signs of improving periodontal disease. A decrease in either of these factors is also associated with improvement in breath odour (11).
An interesting prospective study published in 2014 involved more than a thousand children, starting when they were about seven months old. Half of the infants were randomized to eat a diet restricted in saturated fat and cholesterol, a change that results in higher ingestion of plant-based foods, while the rest of the children ate the usual diet of their family. As the children grew up, tests performed in their teenage and young adult years revealed that those eating the healthier diet had significantly greater production of saliva. Sufficient saliva is essential for the maintenance of oral health and sweeter breath (12).
Extreme diets also play a part in the production of bad breath. Very-low carbohydrate diets, such as paleo or keto diets, consist of predominantly animal-sourced foods and are inevitably low in carbohydrates and high in fat and protein. These foods are also rich in the high-sulfur amino acids that are the preferred food for the bacteria that reside in the mouth. Such diets enhance the production of VSCs in the mouth and increase the probability of developing halitosis (13). Keto diets, which are particularly high in fat and extremely low in carbohydrates, introduce another factor into this situation. They contain so few carbohydrates that the body is forced to metabolize fats instead of carbohydrates for energy. The result is the generation of ketone bodies (acetone, acetoacetate and beta-hydroxybutyrate), detected in the breath as a rotten fruit smell (14).
Why does a plant-rich diet lead to more agreeable breath?
Plants are full of fiber:
Fiber is found only in plants; foods derived from animals contain no fiber at all.
In the infant study from 2014 discussed in the last section, the researchers concluded that the greater salivary flow in the children eating the healthier diet was due to higher intake of fiber-rich food such as whole grains, vegetables, fruit and berries. The extra chewing required to process these foods in the mouth boosts saliva production and results in more efficient self-cleansing of the mouth (12).
A controlled clinical study from 2016 also showed that eating plant-based foods is associated with reduced halitosis. Researchers concentrated on the fiber content of foods and compared the effect on breath odour of eating a single high-fiber meal with that of a low-fiber meal. Two & a half hours after consuming either type of meal, the concentration of VSCs in the breath of the participants had dropped and breath malodour had decreased. Eight hours after consuming the meals, the breath improvements remained in those who had consumed the high-fiber meal while low-fiber meal eaters had returned to their original breath conditions. The researchers pointed out that chewing food has a self-cleaning effect on the mouth and foods high in fiber, necessitating more intensive chewing, are likely to have a stronger cleaning effect than foods requiring less chewing (15).
Certain plants contain nitrates:
High-nitrate vegetables include leafy greens, beets, carrots and celery. Dietary nitrates contribute to the production of nitric oxide by the human body. Nitric oxide stimulates good blood flow, reduces inflammation and aids in the prevention of cardiovascular disease. Eating nitrate-containing vegetables has also been associated with decreased inflammation of the gums.
In 2016, investigators set out to look at the effect of dietary nitrates on mouth health. Their randomized, double-blind, placebo-controlled trial found that, after 2 weeks of ingestion of a high-nitrate containing juice produced from lettuce, significant improvements in gum disease were observed in the mouths of the participants. Improvements in mouth health lead to better-smelling breath (16).
Plants are low in unhealthy fats and sulfur-containing amino acids:
Diets sourced from animal foods contain large amounts of the high sulfur amino acids that feed the bacteria that live on the tongue and create VSCs (13).
Eating a diet very high in fat and protein promotes the growth in the mouth of harmful VSC-producing bacteria (13).
Eating a keto diet, a diet very high in fat and extremely low in carbohydrates, can result in bad breath simply from its generation of malodourous ketone bodies (14).
Plants encourage a healthy microbiome:
Accumulating evidence suggests that, because the microbiota play a critical role in many body processes, our microbes may also contribute to unpleasant body odours originating from the mouth, skin, urine or reproductive fluids. In fact, studies have shown that the microbes that thrive in your mouth are reflective of the microbes living in your gut and encouraging a beneficial gut microbiome will result in healthier types of microbes residing in the mouth. Following a diet high in plants will accomplish this and discourage the presence of microbes in the mouth that have the potential to produce VSCs (1,17).
How to reduce halitosis
Practice good oral hygiene to reduce the number of bacteria present in the mouth. Brush and floss on a daily basis to clear away food particles left behind after eating and discourage the excessive growth of the bacteria living on the tongue that produce VSCs and contribute to halitosis and periodontal disease. Be sure to include your tongue in your brushing routine. In more severe cases of halitosis, inter-dental brushes, tongue scrapers or tongue cleaners can be employed. Research illustrates that reduction of VSC levels in the mouth can be up to 33% with the use of a toothbrush; 40% if using a tongue scraper; and 42% with a tongue cleaner (2,8).
If you have any signs of gum disease, a visit to your dentist is in order. Areas of the mouth that might provide pockets of protection for bacteria, such as ill-fitting dentures, untreated cavities and old or poor dental restorations, should be dealt with (8).
Cutting down on the sulfur intake from your diet can greatly improve breath odour. Remember that the high-sulfur amino acids are derived mainly from animal-sourced foods. Concentrate on eating mostly fruits and vegetables.
Avoid eating raw allium vegetables (onions and the like) for a short while to help reduce halitosis. However, once your breath problem is under control, you’ll want to introduce them back into your diet. Alliums, raw and cooked, are extremely healthy. In fact, their sulfur-containing components that cause transient bad breath are powerful antioxidants that prevent the oxidation of low-density cholesterol (LDL), thus reducing fatty build-up inside blood vessels. You can also limit the malodorous effect of alliums by following up their ingestion with an apple, fresh mint leaves, lettuce or green tea (18,19,20).
Drink green tea frequently. Tea polyphenols, found at very high levels in green tea, have antimicrobial and deodorant effects. Studies have shown that green tea is very effective in reducing VSCs in the mouth, thereby decreasing bad breath. It appears that the antibacterial effect of green tea, along with its suppression of a gene that encodes for an enzyme that creates methyl mercaptan, may be responsible for this beneficial effect (5,6).
Regrettably, other treatments such as mouth rinses and chewing gum offer only temporary solutions. They may mask or reduce offensive breath odour, but the only route to halting halitosis altogether is getting to the cause of the problem (17).
Summing up …
Sweeter breath is a little-known bonus of eating a plant-based diet. The foods that you choose to pass through your mouth on their way to nourishing your body and the care you take in keeping your mouth clean and healthy are crucial in promoting pleasant breath. Add to this a cup or two of green tea daily and you can likely set aside any worries about the odour of your breath.
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