Who knew that the first six months of life could be so, well, weighty? A new study in the Proceedings of the National Academy of Sciences tracked 800 young Filipino men since birth. They found that those who grew quickest from birth to six months grew taller, had higher testosterone counts, greater grip strength, reached puberty earlier and notched more sexual partners than those who grew more slowly in that same six-month time span.
What about that childhood obesity epidemic we keep hearing about? Is this a barely concealed clarion call to stuff our infant sons?
Hardly, explains Christopher Kuzawa, lead author and a biological anthropologist at Northwestern. Rather, it just shores up what we’ve known for a long time: nutrition early in life — including in utero — can have a permanent effect on metabolism, biological and hormonal systems and organs. (The Filipino baby boys were not, in fact, overfed. They were simply well-nourished in comparison to other baby boys at a time when malnutrition and infant diarrhea was not uncommon in the Philippines.)
The findings confirm a theory called “developmental plasticity,” in which the body adapts based on experience. “At birth we inherit genes from our parents but the body can modify development in response to things like nutrition and stress,” says Kuzawa.
Kuzawa and colleagues predicated their research on a critical but not well-known period in an infant boy’s life during which he actually produces adult male levels of testosterone for the first six months. Apparently, that surge of hormones helps shape characteristics like muscle mass and growth rate, which are enhanced in males.
“We hypothesized that good nutrition in the first six months would be an important influence on all traits that testosterone impacts,” says Kuzawa.
They were right, though it remains to be seen whether the findings would translate to a developed nation like the U.S. Even Kuzawa acknowledges “we’re not at a point where parents should be taking this into consideration when raising their kids.”
The takeaway, then, is that biology should not be used as an excuse. “This proves our genes don’t hardwire our biologic fates,” says Kuzawa.
Incidentally, baby girls did not show the same results; girls that grew quickly in their first six months did not mature quicker. Women, just as we suspected, like to take their time.