A Lot Has Happened Since 1925

How Reliable Is BMI After Menopause?

BMI can be quite a useful screening tool, but it’s a lousy definition, by itself, for obesity. Want one more reason? Take a look at a new study by Hailey Banack and colleagues in Menopause. They’ve found that a BMI of 30 is not a reliable dividing line for obesity in women after menopause.

Poor Sensitivity in Women after Menopause

Banack used data from the Buffalo OsteoPerio Study. The study examined the relationship between BMI and total body fat percentage. Body fat estimates came from DXA scans.

Unfortunately, if you look for a single definition of how much body fat puts you into the range of obesity, you won’t find just one number. Some people say that for women, the number should be 30%. Elsewhere, you might find numbers ranging as high as 40%. So Banack looked at a range of values in her analysis.

Using 35% body fat as the threshold for obesity, screening for a BMI of 30 and above would miss 68% of women with obesity. Even at a threshold of 40% body fat, BMI screening missed 45%.

On the other hand, specificity was pretty good. It ranged from 95 to 99%.

Screening Does Not Define Obesity

The definition of obesity is simple. It’s excess adiposity that impairs health. But just because the definition is simple, that doesn’t mean that a diagnosis is simple. By themselves, neither BMI nor body fat percentage provides an adequate diagnosis of obesity. That’s because clinical status matters.

So what this study is telling us is that menopause is an important factor. After menopause, women are more likely to have extra adipose tissue, even at a lower BMI than you might think.

On the other hand, prior work has shown that the health risks of adiposity might be a little less in older women. Again, simplistic formulas go out the window. But one thing that follows from this study isn’t so hard. Paying closer attention to signs and symptoms of health issues becomes especially important as time goes by.

Click here for the study and here for further perspective.

A Lot Has Happened Since 1925, photograph © Neil Moralee / flickr

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November 18, 2017

4 Responses to “How Reliable Is BMI After Menopause?”

  1. November 18, 2017 at 2:03 pm, Anne Fletcher said:

    I’ve also wondered how the fact that we tend to “shrink” as we age factors into the equation. I’m 2 inches shorter than I used to be, so shouldn’t I have to weigh less than when I was younger to be at a healthy BMI?

  2. November 18, 2017 at 2:34 pm, John Dixon said:

    BMI is generally a good measure of %body fat but our obsession for using the same cut points throughout the adult life cycle if flawed.

    BMI is a good metric for assessing %body fat given sex, age and ethnicity, but the result misunderstood.

    We need to learn how to understand BMI and health throughout the life cycle.

  3. November 18, 2017 at 6:37 pm, Ted said:

    Well said, John. Thanks!

  4. November 18, 2017 at 6:37 pm, Ted said:

    Good point, Anne!