BMI underestimates obesity levels

ninerbuff
ninerbuff Posts: 48,973 Member
in Health and Weight Loss
Recently, body mass index (BMI), which has been widely considered an effective measure of body fat, has come under scrutiny. According to researchers from Weill-Cornell Medical College in New York, the data produced from BMI measures may grossly underestimate a person’s true fat mass.

The study, published in PloS One (2012; 7 [4], e33308), focused on dual-energy X-ray absorptiometry (DXA) scans to determine measures of muscle mass, bone density and fat mass in 9,088 individuals. Researchers classified 64% of those individuals as obese. However, BMI measurements indicated that only 26% were obese. Subjects’ average age was 51.

The scientists determined that to maintain accuracy, a specific BMI cutoff point of 28 for adult males and 24 for adult females should be adhered to when BMI is the sole measure being used. “These new cut-points [increase] diagnostic sensitivity with small losses in specificity,” the authors confirmed.

“Our results demonstrate the prevalence of false-negative BMIs, increased misclassifications in women of advancing age, and the reliability of gender-specific revised BMI cutoffs,” the authors concluded. “BMI underestimates obesity prevalence, especially in women with high leptin levels (>30 nanograms per milliliter). Clinicians can use leptin-revised levels to enhance the accuracy of BMI estimates of percentage body fat when DXA is unavailable.”

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Replies

  • AntWrig
    AntWrig Posts: 2,273 Member
    Very interesting!
  • becoming_a_new_me
    becoming_a_new_me Posts: 1,860 Member
    Don't get me started....Fat is what fat is
  • LaMujerMasBonitaDelMundo
    LaMujerMasBonitaDelMundo Posts: 3,634 Member
    That is applicable for normal weight people who are short, have small frames & Asians. However for overweight people BMI is more accurate. In contrast, it overestimates obesity levels on super fit people.
  • Jac118
    Jac118 Posts: 34
    "A more appropriate cut-point for obesity with BMI is 24 for females and 28 for males"

    24 compared to what it is now - 30? That's a HUGE difference. I'm just a bit confused - 24 as the cutoff BMI seems really low, despite what they found -- no? That would make me obese at like 153 pounds. I used to be 145 and was nowhere near obese. Am I reading this wrong?

    The article, in the limitations header, goes on to say:

    "By our cutoffs, 64.1% or about 99.8 million American women are obese."

    Here's a link to the full article: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033308
  • yarwell
    yarwell Posts: 10,477 Member
    It's a question of definition of obesity really......

    "In 1995, the World Health Organization (WHO) defined obesity based on a percent body fat ≥25% for men and ≥35% for women [15], while the most recent 2009 guidelines from the American Society of Bariatric Physicians (ASBP), an American Medical Association (AMA) specialty board, used percent body fat ≥25% for men and ≥30% for women."

    If that's the basis of your chosen definition then BMI is only an indicator that will correlate with it to some degree of (in)accuracy. Calculate / measure the body fat and you don't need to know the BMI to know if the person is obese.
  • Jac118
    Jac118 Posts: 34
    I guess what it's kind of implying is that in the same way someone could be suuuper fit (and clearly not obese) at a BMI of 30 (like Arnold Schwarzenegger), a person can also be obese at a BMI of 24 - which we consider healthy.
  • mirandamayhem
    mirandamayhem Posts: 772
    I hate the BMI charts. From the age of 0 it is a scare mongerer to many mothers breastfeeding their children, and then throughout the years continues to ignore varying frames with heights etc.

    Edited to add, it's great as a loose guideline, at the end of the day there's enough information out there to find out what sort of weight we should be aiming towards depending on how much muscle we carry etc, but at the end of the day the most important thing is that we feel healthy, and are healthy. That's my main aim.
  • fay_pigu
    fay_pigu Posts: 125 Member
    :noway:
    NOOOOOOOoooooooooooooo


    I was only 1 pound away from just being overweight, now I have read this article I have got even more obese. :sad:

    JK, I think this is a rose by any other name argument ... All this seems to be say is Overweight is the new obese (lets relabel it). Studies based on BMI showing health issues related to weight (in the general population) haven't changed. Healthy eating with exercise is good. Sloth and junk-food is bad.
  • anaussie
    anaussie Posts: 88 Member
    http://www.halls.md/body-mass-index/av.htm
    http://www.halls.md/ideal-weight/body.htm
  • NotThePest
    NotThePest Posts: 164
    In a book filled with research papers, Handbook of Exercise in Diabetes, several of the research papers, used this acrostic, MONW, Metabolic Obese Normal Weight, that little ditty stuck with me.
  • Yanicka1
    Yanicka1 Posts: 4,564 Member
    My BMI right now is 23.6 so almost obese for them? I know that I am way more muscular than most women but it is difficult to accept
  • jetscreaminagain
    jetscreaminagain Posts: 1,130 Member
    Who on earth believes BMI is an estimate of body fat? I don't know one person with even moderate understanding who thinks that BMI has anything to do with body fat much less that such a view would be widespread.
  • myofibril
    myofibril Posts: 4,500 Member
    Who on earth believes BMI is an estimate of body fat? I don't know one person with even moderate understanding who thinks that BMI has anything to do with body fat much less that such a view would be widespread.

    The thing is that BMI is actually an indirect method of calculating body fat. That is one of its uses and there is a rough correlation between the two for many people, though of course not all. In Lyle McDonald's "A Guide to Flexible Dieting" he outlines a table for men and women where they can get an indication of their BF% based on their BMI.

    Now certainly some applications are flawed: in particular with some women (as the OP shows) athletic individuals and also older people. In addition the way healthcare providers use it in the absence of other measures (ie a lazy application) is less than ideal.

    However, as a general tool I think it is more useful than not.
  • benita30
    benita30 Posts: 20
    I found this really interesting because I always thought that BMI mostly overestimated a person's fat mass. I find BMI to be grossly unreliable, but for someone starting out on a fat loss journey, it can be helpful at first.
  • jetscreaminagain
    jetscreaminagain Posts: 1,130 Member
    Sure its a useful tool. Helps people who are 5'8" not try for the same healthy weight as a 6'2" person or a 5'2" person. But it is just a ratio of height and weight. Not fat. You want an estimate of fat there's a bunch of calculators with more sophistication than just height and weight and about 10 seconds more time to take the measurements. Likely to be much more accurate too
  • myofibril
    myofibril Posts: 4,500 Member
    Sure its a useful tool. Helps people who are 5'8" not try for the same healthy weight as a 6'2" person or a 5'2" person. But it is just a ratio of height and weight. Not fat. You want an estimate of fat there's a bunch of calculators with more sophistication than just height and weight and about 10 seconds more time to take the measurements. Likely to be much more accurate too

    Yeah, there are much better methods nowadays without question.

    However, I think it is easy to forget that MFP is not really indicative of the general population as whole. People on here care far more about their health and diet, pay more attention to it, and engage in a much higher volume of exercise and end up with generally far different body compositions. If there is a place where BMI will not be useful it is a fitness site ;)

    As a tool for getting a general idea of fatness over large populations BMI does serve a purpose, although it can certainly be flawed for indivduals.
  • auroranflash
    auroranflash Posts: 3,569 Member
    Great! I'm probably fatter than I thought. :laugh:

    Thanks for the post.
  • half_moon
    half_moon Posts: 807 Member
    BMI is ridiculous no matter how you look at it. For me to be "healthy" (borderline healthy) I have to weigh135. Pretty damn sure I'm feeling healthy and looking good when I'm 145, seeing as I am relatively slim, energetic, and strong at 160. Ridiculous! My BMI says I can even weigh 110. Ok, maybe, but I doubt I would be healthy. I'd probably be in a hospital with an IV in my arm. I spit at the BMI and just go by how I feel and what I look like. We have to deal with enough equations in our fitness journey-- why add such a useless on to the mix?

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