body fat and early puberty in girls: new findings

slate reports on a new study showing a link between body fat in girls and the early onset of puberty. puberty has dropped, on average, about 4 years in the past century. i’ve seen the current avg reported differently in different studies. i’ve seen as low as 10.5, and as high as 11.4 (as averages, that is). but that number has plummeted in the past 30 years. for a long time, studies were inconclusive as to the reason. some suggested it was a physiological response to cultural pressure to enter quasi-adulthood at younger and younger ages. others suggested it was a better diet (more rounded). others suggested it was preservatives in food. but, in the last few years, my observation (really, just my anecdotal observation) is that most studies seem to now be saying the reason is tied to how we eat, and, specifically, to all the junk we eat. there ARE trends to younger puberty in cultures that don’t eat the junk of western culture (and, especially, american culture); but the drop in those cultures doesn’t seem to be as extreme.

does anyone know of a comparative study, showing avg ages from a wide variety of cultures?

anyhow, here’s a quote from the slate article on the new study:

“New study: Now, some new research by Joyce Lee and Julie Lumeng of the University of Michigan and their colleagues offers some clarity. They studied about 350 girls of diverse socioeconomic and geographic origins, all born in 1991. The girls’ heaviness was estimated at 3 years of age and again at 4½ by calculating their body mass index percentile, an indirect measure of obesity, normal weight, or thinness. The girls were then tracked over time for evidence of the onset of puberty. As was expected from previous research, other factors like race, mother’s age of puberty onset, and mother’s education played a role in predicting when a girl would reach puberty. But none of these factors were nearly as important at predicting early puberty as a history of being overweight at age 3 or 4.”

(ht to anastasia)

7 thoughts on “body fat and early puberty in girls: new findings”

  1. Well, as the mother of a 9-year-old, I’d be curious to know what they define as “onset of puberty,” since I think some of the onset is rather invisible or at least unobserved for some time before the major, more obvious things begin. And what about girls who were sticks at the earlier ages, but put on a bit of weight later, say around 7 or 8? And then, let’s continue the study to find out why I have PMS EVERY DAY since I turned 40!! lol

  2. kathy — for studies like this, the “onset of puberty” is always marked by menarchy, a girl’s first period. this is one of the reasons almost all studies of puberty measure onset in girls, not guys, since menarchy is such a moment-in-time; whereas, guys don’t have such a clear start of puberty.

  3. I see. But there’s LOTS of other stuff happening slowly but surely before that first period. And plenty of time to put on/take off/grow into body fat before then, as well. So I’m just not too quick to buy the correlation between body fat at age 3 and onset. “But none of these factors were nearly as important” – it could be argued that the mother’s education level could be a contributing factor to weight (i.e., more $$$ equals more discretionary spending on food), but how does my going to college (or not) determine when my daughter starts her period? Just a thot.

  4. I can’t think of anything off hand, but you might be able to look for studies that prove the opposite, that a low body fat percentage staves off puberty. This usually happens with young athletes.

    If you figure, say, for girls with eating disorders, they lose their period because of low body fat… Maybe it just takes less time for girls to gain that body fat due to cultural influences.

    Kathy- One thing I’ve heard is that people in lower income families tend to be overweight due to the fact they can’t buy healthy foods (they are more expensive). So I’d ponder it’d have the opposite effect- that girls in lower income families would have an earlier onset of puberty, granted the body fat percent is the decisive factor.

    I’d love to hear what else you find on this topic!

  5. Marko I appreciate you bringing up this topic. Could you perhaps let us know your thoughts on ramifications of this for youth ministry? I.E. The ongoing debate of emotional readiness of a 6th grader for middle school.

  6. chris — i’ve always felt the drop in the avg age of puberty onset was the strongest reason for 6th graders being in middle school. the teenage years — i’ve said for years — do NOT start at 13 anymore. culturally AND physiologically, the teenage years start at about 11.

    however, i’ve been wrestling with this quite a bit lately, in terms of what’s best vs. what’s normative. i’ve posted about it three times (maybe you missed those): here, here, and here.

  7. Both of my daughters have precocious puberty, and are now on medication to stop the process. The thing is – no one knows for sure what causes this. It could be a number of things. Our pediatric endrocronlogist has basically told us that “no one really knows”.

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