BehindTheMedspeak: Is obesity an infectious disease?

They laughed when Barry Marshall said ulcers were caused by bacteria and curable with a week or two of antibiotics, but by the time he won the Nobel Prize in 2005 for proving it, the laughter had long since stopped.

Now comes a group of scientists from Washington University in St. Louis with the same hypothesized cause for the epidemic of obesity that's sweeping the developed world.

Two studies describing their experiments were published last week in the journal Nature.

Here's a link to three videos about the findings, narrated by Dr. Jeffrey I. Gordon, the scientist who led the work.

Here's the first paragraph of one of the studies.

Microbial ecology: Human gut microbes associated with obesity

Two groups of beneficial bacteria are dominant in the human gut, the Bacteroidetes and the Firmicutes. Here we show that the relative proportion of Bacteroidetes is decreased in obese people by comparison with lean people, and that this proportion increases with weight loss on two types of low-calorie diet. Our findings indicate that obesity has a microbial component, which might have potential therapeutic implications.

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Here's the abstract of the second.

An obesity-associated gut microbiome with increased capacity for energy harvest

The worldwide obesity epidemic is stimulating efforts to identify host and environmental factors that affect energy balance. Comparisons of the distal gut microbiota of genetically obese mice and their lean littermates, as well as those of obese and lean human volunteers have revealed that obesity is associated with changes in the relative abundance of the two dominant bacterial divisions, the Bacteroidetes and the Firmicutes. Here we demonstrate through metagenomic and biochemical analyses that these changes affect the metabolic potential of the mouse gut microbiota. Our results indicate that the obese microbiome has an increased capacity to harvest energy from the diet. Furthermore, this trait is transmissible: colonization of germ-free mice with an 'obese microbiota' results in a significantly greater increase in total body fat than colonization with a 'lean microbiota'. These results identify the gut microbiota as an additional contributing factor to the pathophysiology of obesity.

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More on this work here.