An unusual oral microbiome signature associated with obesity

Some people with obesity have a distinct oral microbiome—a discovery that could lead to a way to detect and possibly prevent the condition early.

The vast community of microbes that reside in the gut can contribute to weight gain in a powerful way associated with obesity and other conditions related to metabolism. So far, however, there is evidence that the oral microbiome that resides more than 700 species of bacteriaparticipates in obesity or in general health was more limited.

“The oral microbiome is the second largest microbial ecosystem in the human body, so we decided to investigate whether it is associated with systemic diseases,” he says Aashish Jha at New York University Abu Dhabi in the United Arab Emirates.

He and his colleagues took saliva samples from 628 Emirati adults, 97 of whom were obese, and sequenced them to see which microbes were present. The researchers compared them to 95 individuals from a group who were a healthy weight but otherwise similar to the obese in terms of age, sex, lifestyle, oral health and frequency of brushing.

The comparison revealed that the oral microbiomes of people with obesity contained more bacteria that cause inflammation, such as Streptococcus parasanguinis and Actinomyces oris, and others Oribacterium sinuswhich produces lactate. Elevated lactate levels are associated with poor metabolism.

Jha and his colleagues also identified 94 differences in microbial metabolic pathways between the two groups. For example, obese people had enhanced mechanisms for metabolizing carbohydrates and breaking down an essential amino acid called histidine, but were poorer at producing B vitamins and heme, which is important for oxygen transport.

Metabolites produced in greater amounts in obese humans by increased processes included lactate, histidine derivatives, choline, uridine, and uracil. These compounds are associated with symptoms of metabolic dysfunction, such as higher levels of triglycerides, liver enzymes, and blood glucose.

“Putting this together, a metabolic pattern emerges. The data point to an inflammatory, low-pH, carbohydrate-rich oral environment in obese individuals,” he says Lindsey Edwards at King’s College London. “This study provides some of the clearest evidence to date that the oral microbiome reflects and may contribute to the metabolic changes associated with obesity.”

So far this is only an association, so cause and effect still need to be separated. “Some of these associations are mind-boggling to me, but at this point we can’t say anything about what’s causing it, so that’s the next step for us,” says Jha.

To determine whether it is the oral microbiome that causes obesity or is altered by the condition, Jha and his colleagues plan follow-up experiments that will focus on saliva and the gut microbiome to see if there is any movement of microbes or metabolites from the mouth to the gut.

Jha thinks it could be possible, but says his hypothesis is that our mouths are full of blood vessels that support our ability to taste and quickly deliver nutrients to where they’re needed, and these vessels may also allow metabolites to enter our bloodstream directly and affect the rest of the body.

Establishing causation will also require randomized controlled trials and studies that look at metabolic pathways, Edwards says.

It could be that when the diet starts to change, certain elements of the food can be better metabolized by certain bacteria that flourish and start producing more metabolites that can affect our desire for certain foods, pushing people down the path of obesity, Jha says. For example, uridine is known promote greater calorie intakehe says.

If it turns out that oral bacteria can drive obesity, it could pave the way for interventions to prevent it, Edwards says, such as delivering healthy oral microbes through a gel, prebiotics that promote the growth of specific bacteria, targeted antimicrobials or pH-adjusting rinses. “Behavioral interventions such as reducing sugar intake will undoubtedly help as well.”

Although the oral microbiome is a consequence rather than a cause of obesity, its assessment may still be useful. The distinct microbiome shifts could be easily picked up by a saliva test, so they could work as a way to detect obesity early and facilitate prevention, Jha says.

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