Some of them did only consider weight. It is the conclusion of the meta itself a mean BMI couldn't be determined from the 12/17 that had it. I don't think those

Some of them did only consider weight. It is the conclusion of the meta itself a mean BMI couldn't be determined from the 12/17 that had it. I don't think those running the studies are at all dumb. They are often focused on specific things, and to the exclusion of generalizable conclusions. I do find it odd that even mean BMI wasn't of apparent interest in diet studies, but I haven't gone thru each sub-study to see why or why not. I wouldn't feel comfortable reading too much into this one's conclusion. "Low-carb w/o any additional specificity looks like bad news" seems technically fair to me, but actual diets are going to tend to distinguish fat and protein as well as their sources so that isn't a a very logical stopping point for an actual decision. Including core concerns like fat vs protein and plant vs animal sources can yield different conclusions, as the meta linked in the sub-thread above did.