gturner wrote:
How is that "proof" when you're comparing preepidemic obesity with postepidemic obesity, given that the question is whether the spread of a particular bacteria constitutes an actual epidemic? This existence of unsymptomatic, uninfected people prior to the spread of the epidemic doesn't really tell you anything.

gturner, the quoted study does NOT prove that:
bacteria cause obesity in a significant number of cases,
that these bacteria didn't exist prior to 10 years 
an epidemic, recent too? From where exactly did you come up with this, gturner?
The study doesn't even prove unequivocally that there's a link between bacteria and obesity (extremely small sample size, lack of independent confirmation, lack of peer review).
On the other hand, the link between diet, sedentary lifestyle and obesity is uneqivocally proven:
http://en.wikipedia.org/wiki/Obesity
So  the percentage of the overall population that was overweight in 1900 (or 1950, 60...) by comparison to the percentage of the overall population overweight now IS proof (corroborated with all the other proof regarding diet and lifestyle) that most cases of obesity are due to diet/sedentarism.