Wendy Wolfson
RedwoodAge.com

What if obesity was caused by an infection? An intriguing hypothesis by a researcher at Boston's Forsyth Institute, which deals with oral health, suggests that bacteria from our mouths may play a role in making us fat.  

Several studies have linked inflammation in other parts of the body to bacteria that causes gum disease. One study shows that 70 percent of people with gum disease are overweight, compared to 37 percent of healthy people. And in overweight people, gum disease tends to be more severe.

Mouth bacteria is also altered by disease ranging from cancer and heart disease to tooth cavities. The American Heart Association even provides recommendations to dentists, suggesting protective measures when doing dental work on certain heart patients.

But  if obesity is caused by inflammation, and certain studies have suggested that fat itself causes inflammation, could the bacteria involved in gum disease be a cause of obesity?

In a speculative paper titled "Is Obesity an Oral Bacterial Disease?," Forsyth researcher J. Max Goodson, a dentist and PhD, and colleagues at the State University of Campinas in Brazil, measured the bacteria in the saliva of 313 overweight Boston women between 20 and 45 years old. They then used DNA probe arrays to compare the bacteria to that found in the saliva from 232 healthy Boston women over 16 and of normal weight.

The researchers counted a total of 40 different species of bacteria, and found a median percentage of 7 of the 40 bacterial species was greater by 2 percent in the overweight women. Just by looking at their mouth bacteria, researchers could identify 98.4% of the overweight women who had greater than 1 percent of a certain kind of bacteria, selenomonas noxia in their saliva.

'Meager' Data
To be sure, Goodson points out, this is a hypothesis based on strictly association, not causal data. "The data that substantiates it is meager." Goodson said. And the s. noxia bacteria found in increased level in the overweight women studied isn't one of the main bacteria implicated in gum disease.

However, even if certain bacteria changed the efficiency of converting food into calories by a small percentage, over a year, the impact would be quite large.

"The thing that people don't realize is that there are a lot of bacteria in the mouth." said Goodson. "If you get one bacteria that is Selenomonas noxia, it ends up being an enormous inoculum in the G.I. tract."

What exactly causes inflammation remains unknown, but Goodson and colleagues suggest that mouth bacteria could be an indicator of change. "I'd like people to think about the possibility that there might be alternate hypotheses [for obesity]," the researcher said.

A Gram a Day
The sheer quantity of bacteria in your mouth is staggering. According to Goodson, people swallow about a gram of bacteria a day and there are an estimated 700 species of bacteria that live in the mouths of people around the world.

In their paper published in the "Journal of Dental Research," the researchers suggested that the bacteria in saliva could be used to diagnose incipient obesity. And they propose further study to investigate the possibility that oral bacteria could directly cause  obesity.

Prior studies linking obesity to bacteria have been done in mice. Mice with certain sorts of bacteria in their guts had a tendency to gain weight and they could catch the bacteria from each other by eating excrement, a common mouse behavior.

Coincidentally, researchers involved with the Framingham Heart Study noticed that spouses and siblings of fat people tended to get fat themselves, but that could be just because of shared behaviors and eating habits.