BMI (Body Mass Index)

BMI is a great starting point for the vast majority. Of course there are some people who are outliers on it, but like 98% of the time if it says you are obese then you have some weight to lose, i think.

Everybody on weight loss and bodybuilding websites tells themselves that it is not accurate because they don't want to accept those numbers. As you said, it is an accurate guideline for the average person. Most people are in denial about the fact that they are, in fact, quite average.

Seriously, every user of this website cannot be an outlier, despite everyone seeming to believe that they are.

I put quite a lot of importance on it myself. I got down to 4lbs above the lowest healthy weight for my height according to BMI, and as much as I wanted to lose more weight I wouldn't (and won't) let myself go into the underweight category. No matter how often I hear people saying BMI is rubbish, I just can't bring myself to go below what it says is healthy. Especially since most people are usually talking about being overweight according to BMI being rubbish rather than being underweight, though I've heard people say it's useless for saying what's underweight, too.

urloved33 wrote: »

Zedeff wrote: »

Everybody on weight loss and bodybuilding websites tells themselves that it is not accurate because they don't want to accept those numbers. As you said, it is an accurate guideline for the average person. Most people are in denial about the fact that they are, in fact, quite average.

Seriously, every user of this website cannot be an outlier, despite everyone seeming to believe that they are.

Well when my Doctor (md) looked it over...and then at me and then said...no that is not accurate. I believed the Doctor but thanks for that oppressive post.

First off, if a dose of reality is your definition of "oppression" then you must live a terribly unhappy existence. You're only a victim if you choose to be.

Second, your MD knows you better than anyone and probably offers you good advice, so take it. YOUR advice however is not the same as the advice for everyone else, so YOUR scenario has no reflection at all on the utility of BMI as a tool. I am a doctor (MD) myself and I respect your physicians assessment, but his assessment of you does not apply to the MFP community as a whole.

Third, for any of the broad community of doubters on this website, you can review the BMI evidence yourself rather than take others' opinions as gospel. Just plug the phrases BMI, validation, and/or predictor along with "ncbi" (which references PubMed, a publications database) into Google and read what comes up. Here's a small sample of some study conclusions:

Campillo et al, 2006: "BMI is a reliable parameter to detect malnutrition"

Pietrobelli et al, 1998: "Our results support the use of BMI as a 'fatness' measure"

Mei et al, 2002: "...the performance of BMI-for-age is better than that of Rohrer-index-for-age [an alternate assessment tool] in predicting underweight and overweight..."

Chang et al, 2013: In a study specifically looking at people believed to be inaccurately assessed by BMI (elderly patients with abnormally high or low body fat percentages): "...BMI was in better agreement with fat percentage with a smaller mean difference from fat percentage..." and "...BMI may be a better index for older men" when compared against a different index (BAI).

Lemacks et al, 2012: "Pearson's correlation analysis revealed a strong association between DXA adiposity and BMI" in middle aged women.

Geliebter et al, 2013: "...BMI correlated significantly with percentage fat from bioimpedence analysis and air displacement plethysmography [and] DXA. BMI was also the single best predictor of percentage fat...." in severely obese women (again, people claim that the scale doesn't work at extremes).

I check my body fat percentage too, not just my BMI, but I'm not an extreme athlete and I exercise only moderately, so I know I don't have a ton of muscle mass.

At 5'4", I'm definitely in the height range where it's a reasonably good predictor, but I'm small-framed so the top end of a "healthy" weight according to BMI is way too high for me (when I was 145 lb, my highest weight ever, I definitely, definitely looked overweight even though I was healthy according to BMI.) I look and feel best near the bottom of "healthy" due to my frame, although I suppose that would change if I were heavily muscled.

I think the takeaway is that BMI is an indicator, not the only indicator.

If BMI places you in a specific category and you disagree with it, then look to other indicators like body fat percentage, hip to waist ratio etc

For most, BMI is a fairly accurate indicator of a range for which most people will be medically healthy.

peleroja wrote: »

I check my body fat percentage too, not just my BMI, but I'm not an extreme athlete and I exercise only moderately, so I know I don't have a ton of muscle mass.

At 5'4", I'm definitely in the height range where it's a reasonably good predictor, but I'm small-framed so the top end of a "healthy" weight according to BMI is way too high for me (when I was 145 lb, my highest weight ever, I definitely, definitely looked overweight even though I was healthy according to BMI.) I look and feel best near the bottom of "healthy" due to my frame, although I suppose that would change if I were heavily muscled.

I'm similar to you. I'm 5'4" as well with a small frame and the high end of my BMI is definitely too high, but the low end is too low. So I guess I am one of the few that fit comfortably in the middle of my idea BMI. I know this because I have BEEN within my ideal weight range. I still looked a little pudgy because I didn't have enough muscle to appear toned. That's what I think people forget. You can be at the top of your ideal weight and be more fit and healthier than at the bottom of your ideal weight with no muscle.

The real question, it seems to me, is how well BMI correlates with health outcomes. And there is some evidence that significantly underweight and significantly obese BMI numbers are correlated with poor health, but that within those bounds, it is not. See, for example, nature.com/ijo/journal/v31/n1/full/0803365a.html

BMI is a good starting point. Also, there is a more research based around BMI than the other things one might use, so it is more useful in terms of matching yourself up with various studies. Obviously, it is going to be off for people who are on the extremes, but for 90% of the population, it works fairly well.