Comment by aroch

Quite possibly, but I also wouldn't be surprised if it was actually CO. The western-fatty diet, a.k.a the stereotypical US diet, winds up promoting CO output by not only your gut commensals, but by your epithelial cells themselves.

Not really on topic but human microbiota papers from before the late 90's/early 2000's aren't the best -- especially when dealing with metabolic processes and outputs. Available technologies and techniques at the time made studying many commensal anaerobes very difficult.