Overweight?! What's your BMI again?

hiake · Oct 18, 2007

BMI: "Freaking out about nothing"

By Terri Coles

TORONTO (Reuters) -- Body mass index, a measurement of weight relative to height, is often used to classify people as normal weight, overweight or obese, but it has several limitations when used as a personal health indicator.

Kate Harding, a freelance writer who blogs about fat-acceptance issues, put together a body mass index (BMI) photo project to visually show the difference between what we think of as overweight and obese people and who they actually are. The BMI Project aims to illustrate the measurement's limitations in order to address the stigma of its labels.

"A lot of people hear overweight and think 'fat person', where you look at these pictures of people in the overweight range and they look perfectly normal," Harding said. "Even the obese people look more like what most of us would think of as chubby."

The standard classifications for body mass index -- calculated as weight in kilograms divided by height in meters squared -- place a person with a BMI of 18 or lower as underweight, a BMI from 18.5 to 25 as optimal weight or normal, a BMI from 25 to 30 as overweight, a BMI over 30 as obese, and a BMI over 40 as morbidly obese.

The low point of the overweight range was moved from 27 to 25 in 1998, and the obesity category is split into stage one (below a BMI of 35) and stage two (above 35).

In the 1980s, doctors began to use BMI as an individual health metric for determining if a person was of normal weight or overweight, but that use of BMI has several limitations.

The biggest issue with relying on BMI is that the measurement doesn't sort out fat mass from muscle mass, and doesn't indicate anything about fat distribution, said Dr. James de Lemos, a researcher at UT Southwestern Medical Center who has studied BMI as compared to other health measures.

Harding pointed to the classic example of the athlete with a lot of muscle and a low body fat percentage who has a BMI in the overweight range. The measurement also doesn't account for frame size, bone density, age or ethnicity, she said.

As well, BMI and cardiovascular health have a J-shaped relationship, de Lemos said, where the best body mass index isn't the lowest.

Those with BMIs under 23 actually show a slightly higher risk of heart disease, probably related to other illnesses associated with bad heart outcomes that reduce body and muscle mass.

"People who are normal or even slightly overweight might be even better from a cardiovascular standpoint," he said. The risk then increases again as weight relative to height increases.

Body mass index does have some value outside of clinical settings, de Lemos said, because it allows people to track changes in body mass over time. However, there are other measurements that more accurately indicate health risk, he said.

In a study comparing body mass index, waist circumference and waist-to-hip ratio in terms of association with plaque build-up in arteries of the heart and aorta, de Lemos and his research team found that the waist-to-hip ratio measurement remained associated with heart risk even when obesity-associated conditions like diabetes, hypertension and cardiovascular risk factors were accounted for.

Body mass index didn't hold the same association. "There's a much deeper association between waist-and-hip ratio and atherosclerosis than we saw for body mass index and atherosclerosis," he said.

Waist-to-hip ratio is calculated by dividing the circumference of your waist by your hips. Women should get a number below 0.8, and the healthy ratio for men is below 0.95. More belly fat results in higher ratios.

Excess fat around the belly can be dangerous for the heart because it behaves differently in the body. "It's very biologically active," de Lemos said, "and the fat on the hips seems to be at least inert and maybe even protective."

Few people have an ideal waist-to-hip ratio, de Lemos said, including those with a BMI in the normal range. While small changes to reduce waist circumference, and therefore the waist-to-hip ratio, can be helpful and are worth aiming for, he said, the associated risk is also small. "This isn't something that should panic people."

Labels like "overweight" and "obese" can lead to panic too, Harding argued. They can also be stigmatizing, she said, when a person feels and looks healthy but has a BMI that places them in the "overweight" or "obese" category. "I think a lot of people are beating themselves up."

Some insurance companies in the United States now use BMI to classify risk, and adjust their rates accordingly, which means that a person with a body mass index of 25 or 30 may pay more for health insurance than one with a BMI of 23. If a person is 5'6", the difference between a BMI of 23 and 25 is 7.5 pounds.

In her writing, Harding advocates the concept of "Health At Every Size" which focuses on exercise and intuitive eating instead of dieting, focusing on wellness and fitness as a goal instead of thinness, and saying that fat doesn't necessarily equal unhealthy.

"A lot of people are just freaking out over absolutely nothing," she said, "when they're healthier than they think they are."

Source: http://features.us.reuters.com/wellbeing/news/ECD646C8-7DA9-11DC-8F19-62106240.html
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A slideshow of Kate Harding's portfolio on BMI can be found at her website: http://kateharding.net/bmi-illustrated/

potatochip73 · Oct 20, 2007

BMI for asian is slighly lower than the white...so you need to make sure your sourse i correct

bryho87 · Oct 23, 2007

that is true, i got my test done the other week and i'm 9.75% body fat, but i work out a lot on weights and recently started boxing, so BMI index is only good for a lil part of anything. P.S the chart i was measured against was for USA/Canadians under 25, whilst i'm BBC so i wonder if anyone has a chinese BMI chart?

minidee · Oct 27, 2007

yes i like the article! BMI is what is important not how you look!

hiake · Oct 28, 2007

minidee said: ↑

yes i like the article! BMI is what is important not how you look!
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Read the article again... <_< BMI is a very crude measure...

Overweight?! What's your BMI again?

hiake Vardøgr of da E.Twin

potatochip73 Member

bryho87 Member

minidee Well-Known Member

hiake Vardøgr of da E.Twin