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Old 07-20-2009, 06:00 PM   #1  
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Default Beyond BMI - Why doctors won't stop using an outdated measure for obesity.

Taken from Slate...an interesting summary of the history, limitations, and current use of the BMI scale.

http://www.slate.com/id/2223095

Quote:
The new research, which supports earlier findings that being slightly overweight is associated with living longer, has added to an ongoing controversy over how we measure obesity. At the center of this debate is the body mass index, a simple equation (your weight in kilograms divided by the square of your height in meters) that has in the last decade claimed a near-monopoly on obesity statistics. Some researchers now argue that this flawed and overly reductive measure is skewing the results of research in public health.
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A recent critique (PDF) of the body mass index in the journal Circulation suggests that BMI's imprecision and publicity-friendly cutoffs may distort even the large epidemiological studies. (There's no definitive count of how many people are misclassified by BMI, but several studies have suggested that the error rate is significant for people of certain ages and ethnicities.) It's impossible to know which studies have been affected and in what direction they might have been skewed.

Our continuing reliance on BMI is especially grating given there's a very reasonable alternative. It turns out that the circumference around a person's waist provides a much more accurate reading of his or her abdominal fat and risk for disease than BMI. And wrapping a tape measure around your gut is no more expensive than hopping on a scale and standing in front of a ruler. That's why the American Society for Nutrition, the American Diabetes Association, and other prominent medical groups have lately promoted waist circumference measurements as a supplement to, or replacement for, the body mass index.
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Old 07-20-2009, 06:02 PM   #2  
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Personal thoughts - I do think the BMI is limited in it's usefulness, particularly in classifying individuals and for setting individual weight goals. But I disagree with the article title (which I copied to the thread title), calling it "Outdated"...the measure is still fairly good for looking at populations as it was originally intended. I'd rather see the headline read "Why doctors won't stop misusing a measure for obesity".
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Old 07-20-2009, 07:38 PM   #3  
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The BMI was a great tool at the beginning of my weight loss journey...in case the weight of 284#s didn't convince me, that high BMI of 46 did.

For me NOW, the BMI is no longer an accurate measure. When I lost my weight (+135#s), I was left with quite a bit of saggy skin...my doctors estimate 15-20#s at least. So, while the scale weighs me in between 138-147 (my range for the last 18 months in maintenance), I'm really "thinner" but my BMI does not reflect that. In fact, based on my BMI alone, some would say that I could stand to lose more weight. In reality, that would not be a good idea.
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Old 07-21-2009, 09:59 AM   #4  
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Further to this, here is the current philosophy according to the CMAJ --
http://www.cmaj.ca/cgi/content/full/172/8/995
In particular:
BMI and waist circumference are the 2 measures currently used to screen for overweight and obesity and to assess a person's risk of health problems (Table 1). The BMI is strongly correlated with reference measures of body fat (e.g., underwater weighing) and is an indicator of risk of weight-related diseases in men and women. The waist circumference measures abdominal (central) body fat and is strongly correlated with risk of health problems (type 2 diabetes, hypertension, dyslipidemia and the metabolic syndrome, which combines all 3 of these conditions).

Considering both measurements to assess disease risk: Although the BMI and waist circumference are related, the latter provides an independent estimate of health risk beyond that determined by the BMI. It is particularly useful to consider both measures when assessing a patient's disease risk (Fig. 3).

Incorporating BMI and waist circumference into an overall risk assessment: The BMI and waist circumference classifications are derived from health risk assessments in large, heterogeneous populations, and consequently the application of BMI and waist circumference to assess the overall risk of health problems in individual patients will vary from person to person and will depend on the presence of other factors that may influence risk. The BMI and waist circumference should be combined with other determinants of risk (e.g., smoking, concomitant disease, diet, physical activity, and personal and family weight history) to estimate overall disease risk. For example, physical inactivity is a contributor to all-cause mortality and cardiovascular mortality, irrespective of BMI.3 What may be underappreciated is the importance of BMI and waist circumference compared with the other, more traditional, risk factors. Until recently, obesity was considered to increase the risk of coronary artery disease through its association with hypertension, dyslipidemia and diabetes. However, a BMI of 30 kg/m2 or greater is an independent risk factor for coronary artery disease, conferring a 2- to 4-fold increase in disease risk, which is comparable to the effect of hypertension on risk of coronary artery disease.

So, it kind of isn't one or the other. Both are valuable for different reasons as they are determinants of different things. One reflects body fat, the other reflects disease risk. But there are some absolutes: BMI over 30, for example, or inactivity. The article also says that both of these measurements should be used with caution for a number of different populations, the elderly, non-whites, and people with healthy lifestyle habits when determining treatment options for patients.

Kira

Last edited by kiramira; 07-21-2009 at 10:04 AM.
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Old 07-21-2009, 12:47 PM   #5  
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Wow, that's awesome that Canada's standard is to look at waist circumference. Unfortunately, too many decisions are made PURELY on a BMI basis, especially for things like insurance coverage/pricing. In the US, considering waist (or ANYTHING beyond BMI) isn't done on a consistent basis.

Even if BMI correlates strongly with % body fat, also, is higher body fat NOT around the waist associated with increased disease? Most studies I've seen looking at long term health outcomes have found that waist circ and activity level have predicted mortality, but I don't know a specific link between body fat % (adjusted for waist size) and health outcomes.
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Old 07-21-2009, 02:30 PM   #6  
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I think the article recognizes that at a certain point, a higher body fat is a definite indicator of disease. This is a BMI of 30 or higher. This absolute value is the cut-off point for "obesity" It doesn't matter where the fat it in this instance -- if you have a small waist circumference and carry the fat in your hips for example, but your BMI is 30+, you are at significant increased risk for CV disease. The following statement is SO important, and the implications are, IMHO, HUGE:

Until recently, obesity was considered to increase the risk of coronary artery disease through its association with hypertension, dyslipidemia and diabetes. However, a BMI of 30 kg/m2 or greater is an independent risk factor for coronary artery disease, conferring a 2- to 4-fold increase in disease risk, which is comparable to the effect of hypertension on risk of coronary artery disease

Why this struck me is that conventional thought believed that if you were obese, your risks were higher because the associated diseases would put you at higher risk of CV issues. Which means that for a long time, it was thought that if you DIDN'T have the associated diseases such as hypertension, your risk of CV issues would be LOW even if you were obese. This is where alot of the FA movements have the philosophy that even if you are obese, you can be fit and therefore have no worries with respect to increased risk of disease. BUT THIS IS NOT THE CASE. Obesity is an INDEPENDENT risk factor -- it doesn't matter what else you have or how fit you think you are, if you are obese, your risk of CV issues is significant by virtue of the fact that you are obese. The cheese stands alone, so to speak

The "grey area" seems to be in the normal to overweight categories. My DH is considered "overweight" by some BMI calculators (6 ft high, ranges between 181 and 183 lbs) BUT when his lifestyle and waist circumference (33 inches) is taken into consideration, he has no worries. He is extremely athletic - cycles, runs, does weights at the gym - so his MD isn't concerned about his BMI. After all, DH at the age of 44 does his "easy" runs of 10km in less than 45 minutes! He bicycled across Canada two summers ago, averaging 140 km per day. With fully loaded panniers. His size and weight has been constant since he graduated from University in 1987 because he works darned hard at it...So despite the BMI, his waist circumference and fitness lifestyle become a factor in determining if he needs to deal with his BMI.

I on the other hand, have a BMI of 26.5 (clearly overweight, BMI wise) and a high waist circumference. Although I do yoga, my lifestyle and waist circumference indicate that I am still at increased risk for various diseases. So I just keep on my path.

I think this goes back to your first observation -- BMI is a great screening tool, but isn't the be-all or end-all, at least up here in Canada. If your BMI is 30+ (you are obese), it doesn't matter what your waist circumference is with respect to certain diseases. If it is in the overweight to normal range, lifestyle assessment and waist measurement becomes another assessment tool to figure out what recommendations should be made and how to prevent those who are overweight with poor lifestyles from becoming obese.

Kira

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Old 07-21-2009, 02:34 PM   #7  
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Another interesting thing in the article is its consideration of the elderly:

Elderly people: Interpreting the BMI and waist circumference in elderly patients requires caution. People aged 65 years or older who are overweight may not be at increased risk of health problems, whereas those who have a BMI in the low end of the normal range (between 18.5 kg/m2 and the low 20s) may be at increased risk. Thus, the normal-weight or low-risk BMI range may be higher and wider (e.g., 22–29 kg/m2) for elderly people than the range for younger adults (18.5– 24.9 kg/m2). Weight loss in elderly people, especially loss of fat-free mass, regardless of the baseline BMI, is associated with an increased risk of death. Consequently, screening for weight loss may be a more useful means of determining health risk in elderly people.

I found this to be particularly interesting -- those with BMI in the LOW end of normal may be at increased risk! Weight loss in elderly people regardless of BMI is associated with an increased risk of death...the recommendation for elderly people is to assess future risk simply by tracking body weight, and going from there.

SO complicated, no?

Kira

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Old 07-21-2009, 02:43 PM   #8  
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Definitely! Weight is so complicated...far TOO complicated to use only one measure as an end-all for recommendations. That's why it kills me to think that my health insurance, were it not employer-provided, would be higher than others, despite my waist circumference and activity indicating I'm at no higher disease risk than anyone else of a normal weight. Also, to think that some people over 65 are being told to lose weight by their docs (this happened to an older friend of mine), even though studies are indicating that is NOT a good idea for her health or longevity.

I do think docs get "blinded" by BMI, and let it cloud their treatment decisions and recommendations, even when there are other factors (small waist, age, activity level, etc) that make BMI less valuable.
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Old 07-21-2009, 02:55 PM   #9  
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You might also want to read this article:

http://archinte.ama-assn.org/cgi/con...c6242eff9f73f1

From the Archives of Internal Medicine, 2002. A study of approximately 15 000 individuals show the correlation between waist circumference and risk of disease, and relates it to BMI measures.

Kira
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Old 07-21-2009, 03:02 PM   #10  
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I think BMI has been ingrained with the medical culture as the be-all and end-all without a real understanding of the grey area. Using such an absolute scale is, well, just down right harmful to alot of people, IMHO. Telling the elderly to lose weight when that in itself may be a risk factor! Because the number says so. Having your insurance rates increase because the number says so! Crazy...how many people are affected by this so the insurance company execs can get their bonuses. It makes NO sense. A comprehensive look to determine risk factors has GOTTA be the standard because anything less is, well, irresponsible and the easy way out. BMI is a great screening tool. If you hit the magic BMI of 30, you are at risk. But the grey areas are just that. There are other factors involved and it is SO EASY to assess risk properly. Just take out a tape measure, ask a couple of questions and have at it!

If you look at the second article, you very well may be at LOWER risk if your BMI is overweight but you are active and your waist circumference is small than for those who are sedentary, whose BMI is high-normal with a high waist circumference. And the insurance companies just don't get this at ALL.

I think what frustrates me the most in the BMI debate are those whose BMI are 30+ yet insist that their Waist Circumference hasn't been considered and if it WAS they wouldn't have a problem. This is where my heartburn starts because a BMI of 30+ IS an independent risk factor. Waist circumference is less of an issue, in these cases.

For me, at 5 ft 7, my BMI is 30 if my weight is 191.5 lbs or higher. Which isn't a super-high weight, when you think about it.

And kind of OT -- thank GOD there isn't mandatory genetic screening -- can you imagine? "The test says you MAY be at risk of contracting X, so your insurance premiums will triple as of today"...SCARY


Kira

Last edited by kiramira; 07-21-2009 at 03:12 PM.
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