BMI vs. body fat percentage

[Twilight 2]

I know there has been some discussion over healthy BMI and I don't want to open up that can of worms. I don't want to debate healthy vs unhealthy BMI. What I was wondering today is about body fat.

Here is my question and reasoning. I have heard and read that being obese causes our bones to become denser and therefore our BMI increases. I don't know how much so. I don't know how much it effects it. Are we talking a point or two or a major increase.

Is BMI supposed to be similar to body fat percent? Is a healthy body fat number the same as your bmi number? I just don't know enough about body fat and was hoping you all could educate me.

Help please.

[Bel 1]

Ok so, from what i have learn't (which isnt much) Body fat is a lot more accurate way of measuring your healthy weight because it scans your body and tells you how much fat you have, bone, Water weight, muscle and exactly how much you can lose to be considered healthy.

Bmi is much more general, how much you should weight is based on simple measurement which in my opinion is too general to be accurate.

My nutritionist measures my body fat by a machine, it says i should be 2kgs heavier then a healthy bmi based on my muscle and fat ratio. I also have very dense bones which the machine takes into account unlike bmi.

Im no expert but wanted to reply :-)

Bel:biggrin2:

[Jachut 487]

Body fat is more accurate than BMI and its what really matters. Its entirley possible to have a "healthy" BMI and still be too fat, just as its entirely possible to have a higher than ideal BMI but be very muscular and not fat at all.

That said, for the average person, BMI is a pretty good indicator of body fat status. People tend to use the old "muscle is heavier than fat" line, when in reality, for most average people, doing average exercise (which can include working very hard) they are just never going to have so much muscle that it throws their BMI into an "overweight" status and I asked my doc specifically about the previously obese people having a higher BMI because of heavy bones and he scoffed at it. He said, yes, our bones are dense as a result of having been heavier, but it would account for a few lb maybe, not significant weight.

The main reason why previously obese people dont get to a "healthy" BMI is multifold - heavier bones, lots of extra skin for sure, but mainly an inability to live on few enough calories to maintain that lighter weight - for some unknown reason we have to eat LESS than normal people to maintain the same weight and its just not maintainable for many.

So for most people, BMI is a good enough indicator. Chances are if your BMI is 28, you are overweight. Not that you have heavy bones.

But that said, I do agree in entirety that you can be slightly overweight and much healthier than someone who's much thinner, AND to be only slightly overweight after years of being morbidly obese, that's quite an achievement.

[Twilight 2]

Thanks for your replies. I hope I get many more as it is very interesting. My gut feeling was that the dense bone doesn't make THAT much of a difference but I didn't know for a fact....I hadn't asked anyone in the know.

I still want to learn more about this body fat vs. bmi debate so I welcome any other answers. Jachut, your explanation was great and I do take what you say seriously. I have found you to be a very knowledgeble and helpful ally in this fight. So thank you for your reply.

Other info that anyone has gleaned from drs or reading? Also, in case I think to ask during one of my appointments....what is "healthy" body fat %. For some reason something about body building and 18% is sticking in my head, but I don't remember where I got THAT number. Is this something I can just search for? I guess I should just try instead of ask here, but then it wouldn't open a conversation I guess....

Thanks for your help all.

[MacMadame 81]

The formula for BMI is based on your height and weight. That means if two people have the same height and weight, they have the same BMI. But they don't necessarily have the same body fat %. In fact, most likely, they don't -- one is bound to have more or less muscle than the other.

You can't know your body fat % from a chart either. It has to be measured just for you.

Some machines that measure it are more accurate than others. My scale measures it by shooting electrical current through my body via my feet. This is considered reasonably accurate though it's not the most accurate. (The most accurate method requires a a swimming pool -- not something I keep in my bathroom. :biggrin: ) The caliper method is the least accurate.

What is considered a healthy body fat % varies. But for adult women, it's usually 18-22%. Mine is 74% :thumbup:

[Jachut 487]

Hmm, I thought it was 20 to 25% for adult women?

Anyhow, whichever, its a good case in point. My body fat level is 25% on the knocker. Which with a BMI of 22 is a good indicator about how your BMI can be low, but your fat content higher. I'm not a muscular person, despite exercising hard and regularly. I'm finer built. Which means that could I achieve it, it would probably be perfectly healthy for me to have a BMI of 19 or so.

Its so individual. We've had all those heated debates about BMI but someone with a BMI *could* conceivably have no more fat than I do, therefore be no less *ideal*. But then again, they could have a BMI which places them overweight and a body fat level that still has them well and truly obese. Everybody is different.

[MacMadame 81]

It depends on what article you read, Jachut. I check before I posted and found 18-22 on 3 articles and 22-25 on one article. So I went with the majority. :tongue:

My goal right now is to get down to 50% so it's all moot to me. Once I get to 50%, I'll worry about whether it should be 25 or 22. :cool2: Actually, my current goal is to get under 200. Then to get to 50% body fat. I like to take it in small steps.

[Pizzaman 0]

IMHO, BMI is bunk for many people.

I intended to reduce my weight to about 190ish (I'm 6'1") and even at that weight, my BMI would show me a little overweight (25.1 BMI). People who know me say I shouldn't lose that much weight because I'd be too scrawny because I am somewhat muscular (it's become more evident once I shed much of the fat that was around my upper body :frown: ). In fact, at my present weight of about 240 pounds, most people say I should lose about another 20 pounds and I'd be perfect. 6'1" and 220 pounds would leave me at a 29 BMI.

Another argument not to rely on BMI's alone. You'll know when you're at weight that you feel good with.

[KarenG. 0]

I am part of a lap band study so I get the Tanita scale print-out. It says that the desirable range for body fat is 22-33% for women. I am was at 37% about 15lbs ago. I think the reange is pretty big.

[jjsmiles 3]

I am also confused about this. I also have access to the Tanita Body Composition Analyser (you can find out more about this by googling) through my WLC. Anyways, I got the printout on April 4 which indicated that my Fat % was 40.2%, and when I got my printout on May 2, it was down to 33.4%, although I had only lost 2.8 kg (or 6.16 pounds) in that 28 day period. It never occurred to me to ask for the printout before, so I don't have any data to compare it too.

According to the same printouts, my fat mass (my weight that is actually fat versus other stuff) went from 38.8 kg to 31.2 Kg. The same machine also says that the desirable range for fat % is 23-34% (although when I googled the result, 34 % is in the "poor" range. I am excited that for the first time in my life, I may be "poor" but at least on one list, I am in the "desirable" range) . Jachut, according to the printout, my target BF% is 20%, so you were right.

Now I am not complaining, because the numbers look great to me, but I don't get the math. I am exercising a great deal (both cardio and weights), but I don't get that big of a change from one month to the next.

At least with a BMI chart, I know that I am officially "obese" (I just got downgraded from severe obesity - woo hoo).

Edited May 4, 2008 by jjsmiles
Add some info

[jjsmiles 3]

I was just reading the responses again and I noticed that McMadame indicates her Fat % is 74%. Again I don't get the numbers as she only weighes 12 pounds more than me. I am 5' 4" 1/2.

[PennyLane 0]

Here's a commercial hydro-testing body fat composition company. It's the kind that uses the swimming pool/dunk tank thing. They have locations all over the place it seems, for about $50 a visit (so you can't really go every week but a few times a year to check up on your progress wouldn't be too terrible). I'm nervous to go myself. A large part of me just doesn't want to know this kind of information. It's bad enough knowing my BMI/weight. I'd hate to have images of my body fat percentage floating around my head. I've got issues to work through, I suppose.

Anyway, here's the site:

Hydrostatic Testing | FitnessWave : Body fat testing - hydrostatic body fat testing - body fat equipment

[MacMadame 81]

I was just reading the responses again and I noticed that McMadame indicates her Fat % is 74%. Again I don't get the numbers as she only weighes 12 pounds more than me. I am 5' 4" 1/2.

Well, that's what my Tanita scale says. I haven't gotten the more expensive and elaborate, but more accurate test. I also haven't measured lately so maybe with my 5 lb. lost, it's gone down a bit.

I am only 5'1" and I have a small frame so there is room for lots of fat. Also, I'm betting at least 10% of that is in my boobies.

[Kristin1031 0]

My surgeon use a BodPod to measure your Fat % ratio to Lean mass Ratio and it also give you the # of Calories you need to maintain your current weight if sedintary or active or very active.

I went from a BMI of 47 before surgery to 36 today. I also have lowered my fat % to 49% it was 59% so I think that is an improvement but I was very disappointed that it was not more. I work out 6 days a week religiously and my body as changed enormously in the 6 months since surgery. Both in mass and fat at least to the naked eye. When I tell people that I still want to lose 70 more pounds they think I am nuts.

I am just looking at my body not at the numbers anymore because it is so depressing.