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The best body mass indexes for low mortality rates

The views expressed are those of the author and are not necessarily those of Scientific American.


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ideal bmi healthy adultsWant to pencil in a healthy target weight for that New Year’s resolution? A new analysis of data from 1.46 million adults has zeroed in on the body mass index (BMI) with the lowest risk of death from any cause—and they aren’t the ones that most tilt the scales downward.

For healthy white adults who don’t smoke, those with a BMI (based on height and weight but not body composition) between 20 and 24.9 had the lowest risk of death after a median follow up period of 10 years, according to the new report, which was published online December 1 in The New England Journal of Medicine. For a 179-centimeter (five-foot nine-inch) tall individual, that would be a weight between about 61 and 76 kilograms (135 to 168 pounds).

The researchers analyzed data from 19 studies that collected information on height, weight, lifestyle and demographics from non-Hispanic white adults ages 19 to 84.

With the abundance of data, "we were able to evaluate a wide range of BMI levels and other characteristics that may influence the relationship between excess weight and risk of death," Amy Berrington de Gonzalez, of the National Cancer Institute and co-author of the new study, said in a prepared statement.

Berrington de Gonzalez and her colleagues controlled for age, alcohol consumption, education, marital status, physical activity as well as variation across studies. (Most of the information collected in the various studies was self-reported by the subjects, but the researchers developed an algorithm to adjust calculated BMIs based on common self-reporting errors.)

Two thirds of U.S. adults are currently considered overweight or obese (having BMIs 25 and over). The new range of lowest mortality risk for healthy non-smokers falls within the current span of "normal" BMIs for men and women (which is 18.5 to 24.9).

When the whole subject population was assessed, however, those with higher BMIs (22.5 to 24.9) had the lowest mortality rates. But when the researchers omitted current and former smokers as well as those who reported cancer or heart disease, the optimal BMI range was 20 to 24.9. (Those with the lowest BMIs were the most likely to be current smokers, but those with the highest BMIs were the most likely to be former smokers.)

As the report authors note, underweight individuals (those with BMIs 18.4 and under) are a tricky bunch to assess and might still be skewing some of the results. Some might be slim due to undiagnosed illness that could increase their risk of an early death, and others might be leading a healthy, active lifestyle that could help them live longer. And the longer the follow-up period, the lower the mortality rate for people with lower BMIs, the researchers found. (Because the new study was a meta analysis of previously collected data, the researchers were not able to track the impact of weight loss or lifestyle changes on mortality risk.)

Those at the upper reaches of the BMI scale had the highest mortality risks. Obese women (those with BMIs of 30 to 34.9) who had never smoked and didn’t report any disease at the outset of the study period were about 44 percent more likely to die during the follow-up period than those with BMIs of 20 to 24.9. That likelihood doubled to 88 percent for otherwise healthy women with BMIs of 35 to 39.9, the researchers found. As of 2008, some 17 percent of non-Hispanic women in the U.S. had BMIs 35 and above, the researchers noted in the paper.

In addition to the high rates of obesity in U.S. adults, the pattern might be especially worrying with the growing number of overweight young people. The researchers found that the overall increased risk of death for those with BMIs 25 and above was strongest in individuals who had topped that number before the age of 50.

Image courtesy of iStockphoto/GOSPHOTODESIGN





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  1. 1. AndrewJayPollack 7:35 pm 12/1/2010

    Very little angers me more than the use of the bullshit pseudo-science measurement.

    I am 5’9" tall. I am 215 pounds. According to BMI, I’m not just fat, I am "Morbidly Obese".

    What it doesn’t mention is that I am also a Firefighter, that I practice Karate 2-3 times a week, or that I have a 34" waist and a 49" jacket size.

    When I try to float in the pool, I sink to the bottom and can lay there holding my breath.

    In other words, I probably have a lower body fat percentage than most of the idiots using that chart.

    If they combined just ONE more measurement in that damn chart, it could ALMOST be meaningful. Suppose a measurement of wrist size, which would fairly well indicate the kind of bone structure someone has. For me, that’s nearly 8" around my wrist. To get me to drop 50 pounds would take a few months of chemotherapy and I would NOT be healthier at the end of it.

    Morons.

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  2. 2. djsxxx 5:51 am 12/2/2010

    Good point. BMI calculated from weight/hight is a pretty useless measure that ignores bone size and muscle mass. If you are going to do a study, get the resources to do it right. You might have fewer subjects but at least you can trust the results.

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  3. 3. Blackpriester 7:51 am 12/2/2010

    Andrew – imagine how happy powerlifters and bodybuilders are with health insurances now using BMI as a "health indicator". After all, THIS guy (http://theswole.com/wordpress/wp-content/uploads/2009/05/flex_wheeler.jpg) is CLEARLY morbidly obese ;) .

    While BMI may be statistically relevant for the US population as a whole, it is HIGHLY unfair to people who are active in strength-based sports. Without fat percentages (or at least taking in the chest-waist ratio in males) it is simply unusable as an indicator of an INDIVIDUAL’s physical fitness level.

    I’d love for SciAm to critically report on studys that "reverse-use" BMI this way.

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  4. 4. HugoM 8:07 am 12/2/2010

    Doctors like BMI because it is slightly difficult to calculate – not too difficult, but enough to convince the average person in the street that doctors are intelligent.
    We find that waist measurement is a far more accurate predictor of heart disease and a whole host of other conditions (and there are different threshold waist measurements for eg Asian males from caucasians, men from women etc). But perhaps this is too simple?

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  5. 5. jbairddo 8:14 am 12/2/2010

    Of course, SA not reporting the other side is not unusual. Waist size has shown as much or more health implications than BMI.
    (see http://diabetes.webmd.com/news/20050310/waist-size-predicts-diabetes-risk)or a more integrative method combining both at http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/bmi_dis.htm.
    Of course my favorite screw people with body weight is "Biggest Loser" which penalizes people who actually build muscle and lose fat as opposed to those who just burn calories and lose muscle and body fat. If that show ever used body fat %, many of those sent home as losers would be winning big time. Oh well, nobody ever said entertainment and science were meant to go together (thank god or mythbusters would go under fast)

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  6. 6. vmfenimore 8:57 am 12/2/2010

    My impression of these studies is that the scientific community has already concluded that a bmi of between 18.5 and 24.9 is healthiest and will ignore data to prove it. This headline could just as well read, "BMI under 22.5 is just as dangerous as BMI of 25 to 29.9".

    Obviously being a normal weight and reasonabley fit is healthiest but measurements such as BMI and lbs don’t always reflect that. Even waste size does not account for that 6 foot amazonian woman who is naturally wide waist-ed.

    I’ve always been large under my fat (ie bones and muscle) and even when I was thin I was constantly made to feel fat. At 17 in a swimming class our instructor measured everyone’s body fat (under water and with calipers) and she told me I was 17 or 18 %. There was another tiny petite girl in the class who came to 25% body fat. Society would have definitely viewed her as the thin one. I think there is a definite bias against people with large frames who are well muscled. It seems worse for females.

    Unfortunately I think this bias helped contribute to my current obesity. I first dieted at age 11 when I was 5’4" and weighed 118 lbs. I lost 6 lbs and got down to 112. I realize now how ridiculous that was but I was responding to constant comments about how I was a big eater, I was not skinny and I would have to watch my weight when I grew up. I now realize that I never was over 18% body fat until after the age of 18 yet I felt borderline chubby my entire childhood.

    Looking around I realize that I was not the rare genetic exception these studies like to claim people like me are. There are many women who are big not fat yet the weight charts and bmi calculations are making them feel 20 lbs overweight. I feel the long term physiological results of that is to make these people feel like simply giving up.

    On top of all that, it has been proven that weight does have a large genetic component. Yes food makes you fat, but appetite makes you eat food.

    I am 45 with hardly any gray hair, young looking skin, no varicose veins, great bone structure, respectable iq, hardly any cellulite and I don’t get to take any credit for any of those traits, because they are genetic but my weight is all my fault. Hmmm. Perhaps if everyone used their brains, flexed their muscles correctly, took care of their skin and hair, and thought only nice thoughts they would have all of my good traits ?

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  7. 7. CoMtMan 10:15 am 12/2/2010

    My employer adopted physical criteria to earn $750 in annual health funds to cover deductibles. The criteria were BMI 25.1, BP 120/80, and LDL 100. A year and a half ago, I began increasing my exercise level from about 10 miles of mountain hiking per week in summer and 5 miles in winter to nearly 20 miles in summer and 10 miles in winter. I rode my bicycle 2,400 miles in less than a year. I hiked to 28 summits above 14,000 feet, with several other long ascents without attaining such high summits. My BMI and other vital signs remain flat.

    Here is my commentary, written six months ago:

    The United States Winter Olympics Team were healthy enough to earn a heavy load of medals last month. However, many of these top athletes would not qualify for a health benefit award based on Body Mass Index [BMI].
    Weighing 203 pounds, standing 6’2″, Bode Miller won gold, but his BMI of 26.1 disqualifies him from wellness benefits. Based on “normal” BMI criteria of 24.9, other Olympian winners who are overweight or obese: Seth Wescott, 27.3; Jeret Peterson, 26.5; Andrew Weibrecht, 29.9; Steven Holcomb, 31.6; Justin Olsen, 29.2; Steve Messler, 27.8; and Curtis Tomasevicz, 30.6.
    At least 24 Gold Medalists from the 2004 Summer Olympics also join this list of althletes who are considered overweight or obese against the BMI standard. Of course, all of the athletes reside in countries where health care benefits are not based on their BMI, except for sprinter Shawn Crawford, 26.0, from the United States.
    Under the BMI criteria, two-thirds of citizens in the United States are overweight or obese. The poor health condition of these citizens allegedly costs $147 billion a year. Contrary to this conclusion, a Swedish study of participants revealed that Olympic athletes with lean BMI were almost twice as likely to suffer recent illness compared to those with higher BMI, leading to at least higher short-term health care costs.
    According to a recent North Carolina study, 43% of all deaths are unnecessary. North Carolina researchers conclude that the secret to a 5 pound annual weight reduction for the obese citizen on the road to immortality is an 18% tax on junk food. If the evil of the next millenia is fat, then the penalty of sin can presumably be shifted to the fat-pushers rather than punishing the health care insurers, providers, and patients.
    Aside from possible objections from food producers, retailers, restaurants, and a few diners, a wellness tax on fat could be implemented on the basis of a dime per gram of fat in any food item. The proposed tax would add $4.00 to the price of a bacon cheeseburger; $2.70 on an order of large fries; $9.60 for a pound of pork sausage; $5.10 on a vegetarian pizza; $3.60 on a box of breaded fish; $7.80 for a bag of tortilla chips; $3.20 on a box of cereal; and $44.80 on a pound of butter. Such a wellness tax will either raise enough revenue to provide health care for all Americans or create a lean citizenry with BMI that achieves the wellness standard.

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  8. 8. hsr0601 9:05 pm 12/2/2010

    "1. Meat Lovers & Weight Gainers : The Distinction In America
    "

    2. We are living in an age of Automation , naturally so the excess diet is more likely to work against wellness since the residues lingering in our body should act as a hot bed for all forms of germs, bacteria, virus and the likes, which I think spread to a variety of diseases including diabetes, depression & mental diseases & beyond.
    For instance, after eating much, we might feel so depressed. 
    That is why obesity is called an epicenter of plentiful diseases costing hundreds of billions of dollars annually.  

    3. Parents might want to turn focus from their marriage life to the education of children. 

    A common knowledge has it that the unceasing affection & dedication of parents keep their amiable children off all harmful things. 
    At the moment, the country is struggling to find out how to heighten the educational level.  

    I guess the first & critically vital step needs to begin with parents’ ardent zeal, which encourages their adorable children to use a computer mainly for educational needs, and doesn’t accept unqualified teachers. 

    It might be worth noting that the especially ardent dedication of Mozart’s father is behind his greatness.  

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