Fecal transplants from obese individuals to lean individuals can cause the recipient to develop obesity, suggesting gut bacteria play a causal role.

“our guts are messed up and there's a whole phenomenon called metabolic endotoxin has been well described and studied and the fact that your gut microbiome plays a huge role in regulation of weight independent of calories so they literally can take the poop out of a skinny rat into a fat rat and make them skinny and vice versa they've done in humans”

“so the hypothesis here has to be pretty clear that the uh gut bacteria of the obese individual is playing a causal role in their obesity”