Can Saliva Reveal a Risk for Obesity?

Could something as straightforward as saliva indicate a person’s risk of obesity? Scientists now think it may be possible.

Fresh research has found that people with obesity carry a different balance of mouth bacteria from those at a healthy weight.

The finding may one day allow doctors to identify obesity sooner and potentially help prevent it.

Mouth bacteria and obesity

Trillions of microbes live in the human body. The gut microbiome is widely recognised for its influence on digestion, body weight and metabolism.

Yet the mouth is also home to a substantial microbial population. The oral microbiome is the body’s second-largest microbial community and contains more than 700 types of bacteria.

A research group headed by Aashish Jha at New York University Abu Dhabi investigated the oral microbiome. Its aim was to establish whether bacteria in the mouth are linked with conditions affecting the entire body.

The scientists took saliva samples from 628 Emirati adults. Of these participants, 97 had obesity. They compared these samples with saliva from 95 adults of a healthy weight.

The two groups were alike in age, sex, lifestyle, oral health and tooth-brushing habits. This enabled the team to concentrate on body weight as the key difference.

Inflammation and harmful chemicals

The research revealed distinct differences in oral bacteria. Participants with obesity had greater levels of bacteria linked to inflammation.

These included Streptococcus parasanguinis and Actinomyces oris. The team also detected higher amounts of Oribacterium sinus, a bacterium that produces lactate.

Lactate is associated with impaired metabolism, the process through which the body converts food into energy. If metabolism is not functioning properly, blood sugar and fat concentrations can increase.

The researchers identified 94 differences in the ways bacteria processed nutrients as well. In people with obesity, bacterial activity involved more active breakdown of carbohydrates.

Functions of mouth bacteria

The bacteria also broke down histidine, an amino acid, more frequently. Meanwhile, these bacteria made fewer B vitamins and less heme, which helps transport oxygen in the blood.

Saliva samples from people with obesity had increased concentrations of several chemicals. They included lactate, histidine by-products, choline, uridine and uracil.

Elevated amounts of these chemicals are linked with higher triglycerides, raised liver enzymes and increased blood glucose.

A pattern in the oral environment

Once the researchers considered all the findings together, a distinct pattern emerged. The mouths of people with obesity had a more acidic environment.

Their bacteria processed a greater quantity of carbohydrates, while the oral environment also displayed more indications of inflammation.

This pattern could represent changes occurring elsewhere in the body. The oral microbiome may reflect metabolic health. Scientists are also exploring whether mouth bacteria could have an effect on weight gain.

Future research directions

Although the study demonstrates a strong association, it does not establish cause and effect. Scientists must still resolve a key question: do mouth bacteria lead to obesity, or does obesity alter mouth bacteria?

Further studies are planned to investigate this. Future work will assess both saliva and gut bacteria. Scientists intend to determine whether bacteria or chemicals can travel from the mouth into the bloodstream or digestive system.

There are many blood vessels in the mouth, and they rapidly transport nutrients through the body. Some scientists propose that chemicals produced by mouth bacteria could enter the bloodstream and influence metabolism.

Controlled experiments will be required to demonstrate this. In-depth research into bacterial processes will also be useful.

Saliva tests may detect risk

Dietary choices could contribute to these changes. When eating patterns shift, certain bacteria may multiply more quickly. Such bacteria can produce chemicals that heighten hunger. Uridine, for instance, can cause someone to consume more calories.

Should scientists confirm that mouth bacteria have a role in obesity, doctors could create new treatments. These might involve gels containing beneficial bacteria, products that encourage good bacteria to grow, medicines that destroy harmful bacteria, or mouth rinses that lower acidity. Reducing sugar intake would remain important.

Even if obesity is responsible for changes to mouth bacteria, saliva testing could still be valuable. A straightforward saliva test might detect early alterations. Doctors could then identify people at risk and offer support earlier.

Significance of the study

The research demonstrates how closely connected different areas of the body are. Health is not determined by a single organ. A minor change in one part of the body may point to a larger change elsewhere.

The findings also strengthen the case for further research into simple, painless and easy-to-use tools such as saliva tests.

As this work progresses, monitoring and improving health could become more straightforward, faster and more accessible for everyone.

The study appeared in the journal Cell Reports.