Several days ago (in Daf Yomi time) we read of Rava's observation that delayed puberty may be related to body mass:
כי אתו לקמיה דרבא אי כחוש אמר להו זילו אבריוהו ואי בריא אמר להו זילו אכחשוהו דהני סימנין זמנין דנתרי מחמת כחישותא וזמנין דנתרי מחמת בריותא
Whenever people came to Rava [with a case of a man who had not developed pubic hair] he would tell them, if [the man was] thin, ‘Let him gain weight’; and if they were overweight he would say ‘Go lose weight’; for these signs [of sexual maturity] are sometimes delayed as a result of emaciation and sometimes as a result of obesity. (Yevamot 97a)
There has been some discussion of what appears to be the increasingly earlier onset of puberty in girls. In fact, menarche, (the age of a girl's first menstrual period) has been steadily decreasing by a consistent three years per century of record keeping. However, Rava was addressing not the early onset of puberty in girls, but its delayed appearance in boys. He noted that this delay was sometimes related to extremes of nutritional status, and so in these cases, was amenable to intervention.
Rava was on to something. He may in fact have been the first to report an association between obesity and delayed puberty in boys. This association has been confirmed by several studies which found that obesity has different effects on puberty in boys and girls. In girls, obesity is associated with earlier puberty, while in boys it has the opposite effect, and delays sexual maturation. But it was not until 2010 this association was confirmed by a longitudinal population-based study. This reported that a "higher BMI z score trajectory" (i.e. obesity) during early to middle childhood may be associated with later onset of puberty among boys.
Rava also claimed that puberty may be delayed in boys who are underweight, and this has also been confirmed. As far as I can tell, none of the researchers has credited Rava (who died around 350 CE.) for being the first to notice these associations. But Rava was first, and firsts count for something in science.
The same passage is repeated in Bava Basra (155b) but in the name of Rabbi Hiyya. Hiyya probably lived in the second half of the second century, and so predated Rava by a few decades. The claim of primacy regarding the association with nutritional status and delayed puberty may therefore have to be extended back to R. Hiyya. But so far I have found nothing in the works of Hippocrates, Aristotle and Galen that address this issue, so this association does not appear to have been a widely held belief in antiquity that was simply being echoed in the Talmud. As all good scientific papers end, further research is needed...