In reality I think it's likely that different people are overweight for different reasons. Adenovirus 36 infections for example do correlate with overweight.
Partly because "The infection with Adv36 accelerates differentiation and proliferation of the 3T3-L1 human preadipocytes into adipocytes [27,43,44] and increases the concentration of lipid content in fat cells."
Saying it's "calories in, calories out" suggests that the fact that the virus results in more adipocytes (fat cells) in lab cells is irrelevant.
Lab animals with their controlled diets also got more overweight.
Investing money into finding out how to cure Adenovirus 36 seems important to me from a public health perspective but a group of researches of obesity who believe in the calorie in, calorie out maxim won't direct their research that way.
It seems like we have the technology to produce vaccines against some types of Adenovirus.
If it's worth saying, but not worth its own post, then it goes here.
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