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BMI vs Body fat %

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BMI vs Body fat %

Postby SarahC » Mon Nov 26, 2007 11:00 am

I have a couple of dumb/confusing questions

1. What is the lower limit for BMI, ie, the "underweight" BMI. I have heard everything between 18.5 and 20 (now I choose to believe 18.5... I think that came from the world health organisation from memory :? )

2. Is it possible to have a "underweight" BMI, but still be a healthy weight. In my case, I have a very high body fat percentage, not sure exactly what it is, but I'd say at least 25% by now. So yeah if you have a low BMI but high body fat, wouldn't that still be considered a healthy weight.
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Postby Mandie » Mon Nov 26, 2007 11:24 am

Found some information - I think most doctors use what I've been taught, which is 20-25 is healthy, but the WHO (world health organisation guidelines) say:

* Underweight — BMI < 18. 5 kg/m2

* Normal weight — BMI greater than or equal to 18.5 to 24.9 kg/m2

* Overweight — BMI greater than or equal to 25.0 to 29.9 kg/m2

* Class I obesity — BMI = 30.0 to 34.9 kg/m2

* Class II obesity — BMI = 35.0 to 39.9 kg/m2

* Class III obesity — BMI greater than or equal to 40 kg/m2. This type of obesity is also referred to as severe, extreme, or morbid obesity.

The definition of overweight and obesity varies by race. The WHO and NIH Guidelines are currently applied to whites, hispanics and blacks. For Asians, overweight is a BMI between 23 and 29.9 kg/m2 and obesity a BMI >30 kg/m2.


I've also found a good table comparing body fat percentage and BMI: Females Males
African-

American
Asian


Caucasian


African-

American
Asian


Caucasian


Age 20 to 39 Percent fat
18.5 20% 25% 21% 8% 13% 8%
25 32% 35% 33% 20% 23% 21%
30 38% 40% 39% 26% 28% 26%
Age 40 to 59 Percent fat
18.5 21% 25% 23% 9% 13% 11%
25 34% 36% 35% 22% 24% 23%
30 39% 41% 41% 27% 29% 29%

A little confusing! If you go across the top of the numbers, the first column is BMI, the next six are all percentage body fat. Starts with females (first three), then males (second three), and the ethnic groups are African-American, Asian and Caucasian in order (1,2,3 then 1,2,3 for men). Make sense?

WAIST CIRCUMFERENCE: In adults with a BMI of 25 to 34.9 kg/m2, a waist circumference greater than 102 cm (40 in) for men and 88 cm (35 in) for women is associated with a greater risk of high blood pressure, type 2 diabetes, and high cholesterol, and heart disease.


Hope this helps! I'll try to summarise : Basically, underweight is considered below 18.5, but it depends on your ethnic group. The body fat percentages related to BMI are above. Women always have a higher body fat than men. If you have an underweight BMI, you are very unlikely to have dangerously high levels of body fat - anywhere up to and often over 30% is still okay as long as BMI and waist circumference and within normal limits.
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Postby rivenriver » Mon Nov 26, 2007 11:32 am

I found a table

http://lowcarbdiets.about.com/library/b ... charts.htm

It says that for women aged 20-40 (that's you, right?), less than 21% body fat is unhealthy, and 21%-33% is healthy. So by the looks of this, you have nothing to worry about. But maybe you should talk to your doctor? Cos they can measure you and do all the calculations and stuff, cos everyone is different.

Hope that helps. :)
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Postby rivenriver » Mon Nov 26, 2007 11:35 am

Oh, and yes, it is possible to have a BMI of like 17 and still be very healthy, BUT these are usually the people who eat all the time and don't think about their weight at all, those naturally skinny girls who have never heard the word "diet" in their life. I don't think I've heard of someone trying to loose weight to get to a 17 or 16 and still being considered healthy.
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Postby SarahC » Mon Nov 26, 2007 2:04 pm

Thanks Mandie and Marti (hehe that sounds funny :lol: ). What great info! I feel a bit better now :)

Underweight my fat a** hahaha.
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Postby zeedeveelgirl » Mon Nov 26, 2007 3:21 pm

Psh, I'm 21 and my body fat % is 19.5%, which makes me underfat! Heheheh underfat. I still have plenty of fat, thankyouverymuch :P :P :lol: :lol: How will we ever have a true guide to go by?! My BMI is 21.99, so 22, which is classified as Healthy.
Bah, pish posh! This frustrates me :lol: :lol:
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Postby losebabyfat_2005 » Wed Nov 28, 2007 9:18 am

ooo, i'm only just in the healthy range for body fat percentage according to that calculator but my bmi has been in the healthy range since i was about a month into my weightloss journey (this time).....hmmm

body fat percentage:33%
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BMI and %Bodyfat

Postby Haylez » Thu Nov 29, 2007 10:23 am

Hi guys, I just joined the forum today and this discussion interested me.

I have a BMI of 31, which means I'm obese and I look at myself and all I can think is WTF? Even my doctor said to me that if I am very far from being obese.

About a year ago I had a %body fat of 49%. Now my %body fat is 36%, yet I ahve not lost a single kilo.

The problem with BMI is that it does not take into account muscle mass. You may weigh alot due to muscle, but your BMI will say you're overweight, yet teh military uses this to determine if you're a suitable weight to get in.

%body fat is also inaccurate. If you stand on the scales with wet feet, you will get a different reading than if they were dry. Also if you put more pressure on teh scales than normal, you will get a different reading. It also doesn't take into account big breasts. What if a woman is really skinny, but has huge knockers, the %body fat will be high.

A normal, healthy %body fat for a woman is below 30% (going by what the police force asks for)
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% Body Fat
Start: 36.3%
Current: 35.4%
Goal: 27%


1st mini Goal: 80kg by christmas
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