I can't remember which book I read it in, but no, it wasn't about the focal infection, but rather the inflammation markers. Inflammation changes blood chemistry (blood cell mix, the "stickiness," and other chemical markers) and there's good reason to believe there's no such thing as "local" inflammation when it's an internal organ (vs, say, a rash on your elbow). And like circulating hormones in response to a grievous injury, these changes can cause a cascade effect.
Meh, observational data sucks. And the cohort studies (with treatments) don't seem to have been compared with a control group. Just before/after.
Way more important to be lean and active.
I ask because Wikipedia[0] believes that the theory is still quite "out there" but I'd be happy to learn from more up to date/reliable sources.
[0] http://en.wikipedia.org/wiki/Focal_infection_theory