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mattbrowne's avatar

How reliable is the claim that the optimal BMI is 27 because it correlates with maximum life expectancy?

Asked by mattbrowne (31449 points ) January 27th, 2012

The other day I read a short article in a German magazine citing a doctor called Werner Bartens. He mentions studies that point to the fact that an BMI of 27 is optimal for longevity. Unfortunately the names of the studies were not given and when researching the issue online all I get are the standard claims that a BMI of 20 to 25 indicates optimal weight.

Werner Bartens seems to have a good reputation. He got an MD both in Germany and in the US. The German Wikipedia page lists several awards in science journalism.

Does this point an ongoing controversy?

Which BMI studies are reliable?

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13 Answers

keobooks's avatar

Maybe he’s correct if your BMI is that high because it’s all sheer muscle mass and black hole bone density.

mattbrowne's avatar

No, no, he wasn’t talking about athletes. He claims that the extra fat, especially when stored in the buttocks, thighs, and hips, is a good thing. So on average people with a 25 BMI die earlier.

philosopher's avatar

@mattbrowne
You can ask Dr. Mark Hyman about this.
Dr. Hyman is involved in ways to eat to be healthy. Some of his stuff is unbelievable but much makes sense. You can write Dr. Oz too.
As you know every study says, something else. Most are subjective.
I eat Whole Foods and I exercise. I do Aerobic,Yoga and lift Weights. My BMI is in the range my doctor advises. My blood work comes out great because I eat right.
All studies are imperfect.
My doctor looked at the BMI Chart and pointed to my height. I am sure it is not perfect.

wundayatta's avatar

You might search on “pear” vs “apple” body shapes. There’s been a lot of research showing that you want the weight on your hips and thighs, not on your stomach. If you’re fat in the stomach that is not good for life expectancy. Hip fat does not seem to be a problem.

Charles's avatar

Worrying about whether a BMI of 25 vs 27 is optimal will reduce your life expectancy due to stress more than the worst case BMI will.

Judi's avatar

I think BMI is horribly incorrect. If my husband were in a healthy BMI range he would blow away. A healthy BMI is accurate for me. There are much more accurate ways to measure a healthy weight.

bongo's avatar

woah surely 27 is super high?! Ideal is 18.5–25! so having a BMI of 19.14 makes me in the healthy range. 27 is in the “overweight” category.
Underweight BMI less than 18.5
Ideal BMI 18.5–25
Overweight BMI 25–30
Obese – should lose weight BMI 30–40
Very obese – lose weight now BMI greater than 40

All a load of crap anyway. As long as you are healthy, not overweight by looking at yourself and can do moderate exercise easily then there is no need at all to worry about your overall health and weight. The only thing people need to be concerned about is their waist circumference with your risk if diabetes massively increasing when you have a waist circumference greater than 35 inches for women or greater than 40 inches for men.(Obviously this does not mean pregnant women!). You can be normal weight but if your body shape dictates that you have a wider waist then you have higher risk of diabetes whatever your weight.

Judi's avatar

@bongo , A lot of people get body dysmorphia though, and don’t realize when they are overweight. The mirror has a way of lying to us. We need measures, I just think that the BMI is a faulty one.

Uberwench's avatar

My understanding is that BMI is an extremely rough guide that cannot be usefully employed in the absence of other measures and/or expert opinion. I’ve known plenty of people in good health whose BMI scores suggest that they should have died the previous Tuesday. Since there is apparently evidence that being slightly “underweight” is worse than being slightly “overweight,” though, any claim that the optimal BMI is actually above the recommended range is worth taking seriously.

Aethelflaed's avatar

The BMI is really a horrible way to measure fat, and even worse for measuring health. You can read a really wonderful 2-page history here, but to sum up, it was invented in 1823 by someone who wasn’t a medical professional who wasn’t trying to do medical things (he was trying to do some sociological studies on the average build of various populations), and wanted a shortcut to do that. To reiterate, shortcut, non-medical inventor, non-medical purpose. In fact, the inventor actually warned against the idea of using it for any medical purpose.

There are really better ways of measuring fat (where the fat is, hip-to-waist ratio, etc), but it’s also important to remember that fat itself isn’t actually an indicator of health in any way. Underweight is better than overweight, and you really don’t get a whole lot of severe effects until the very extreme end of obesity, but even still, those are statistical averages that don’t automatically mean anything for the individual. And actually, this focus on BMI instead of the actual tests of health (blood pressure, cholesterol, fat/muscle ratio, etc) has a tendency to really aggravate issues with disordered eating and body image issues.

mattbrowne's avatar

@Charles – You seem to misunderstand. I’m not worried. How did you get this impression? I’m looking for scientific clarification here. So your answer doesn’t help at all, I’m afraid. But it’s helpful as a good showcase for the problems of communication. People come up with completely different interpretations when reading the same text.

mattbrowne's avatar

@philosopher – Thanks for the tip!

mattbrowne's avatar

@wundayatta – Yes, I heard about that too.

And I’ve also heard that the BMI should be replaced by something better. Yet it’s still very common.

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