> Obesity can’t explain the entire decrease, however. One large-scale, recent review found a testosterone slump despite researchers’ adjusting for the subjects’ body mass index. “Even among normal-weight men, we see that same decline,” Eisenberg said. Some analyses, he added, have suggested that testosterone has dropped off most profoundly among normal-weight men.
We already know obesity significantly lowers testosterone, and we have never been fatter.
Per the linked article, about midway through:
> Obesity can’t explain the entire decrease, however. One large-scale, recent review found a testosterone slump despite researchers’ adjusting for the subjects’ body mass index. “Even among normal-weight men, we see that same decline,” Eisenberg said. Some analyses, he added, have suggested that testosterone has dropped off most profoundly among normal-weight men.