Nothing stays the same

Womens BMI body mass index changes with age

A chart showing the Body Mass Index of Women, changing with age. Quite interesting, really. I bet you haven’t seen this chart anywhere else!

Womens body mass index BMI chart

Did you make that chart yourself, doc?

I did. I needed to see child and adult curves on the same chart.

There’s something fishy, a gap around age 20.

The CDC growth charts for kids, are deliberately shifted lower, by the CDC, not me.

Notice the "median" BMI value, which is the 50^th percentile Red line. Compare it to the CDC definition of "Overweight" at BMI of 25. This is where the experts derived the famous statistic, that over 50 percent of American Women have a BMI over 25 and hence are considered overweight.

My BMI is 26, but I am NOT overweight.

The cutoff at 25 is the problem.

Ignore the BMI 25 cutoff. Just ignore it. It’s wrong.

Also notice the gradual increase in Women’s body mass index over time, until age 50-60. After that, a gradual decrease in BMI occurs in older women. Each percentile line has a curved shape, even for skinny women at 25^th and 10^th percentiles. ( I’m hinting, without much subtlety, that a curved line is better model than a flat line across BMI=25. I’m hinting, that some weight gain during adult life is "natural".)

Update in 2014. I updated a different page, proving the weight gain is healthy in adults.

The chart shows how girls BMI increases with age, even beyond age 20. The children’s data came from the standard CDC growth charts. There is a gap between the children’s and adult data, because the data sources are different. The adult data (from the NHANES III survey) is more recent ( 1988-1994 ), whereas the body-mass-index-for-age charts from the CDC are based from a mix of data from old and recent sources.

This page also shows a Men’s body mass index chart (below). Comparing Women to Men, you’ll notice some differences. At less than 50^th percentile, men have a higher BMI than women, which is generally thought to be due to men’s greater skeletal muscle mass. But after age 30, for the 50^th percentiles or higher, overweight women rise to higher BMI levels than men. Why is that? Probably because if a woman is going to be overweight, her body accumulates fat in breasts and hips, which are places that men’s fat accumulation doesn’t occur. This female trait probably explains the higher BMI levels in overweight women.

Mens BMI chart

I realize the charts can be hard to read, so the table below shows actual numbers:

Age:	20-29 yrs	30-39 yrs	40-49 yrs	50-59 yrs	60-69 yrs
The “National Average” Median Body Mass Index values for Women are:
Median BMI:	24.4	26.4	27.8	28.4	27.5

So I’m in my 20s, and the average body mass index for women, like me, is 24.4

And the number get into the 27 and 28 BMI range in older adults. That’s Normal, not a disease, not overweight.