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My BMI is 30.4 and it says I am obese. But I dont look obese. One doctor was surprised at my high BMI value. She said maybe I have high bone density or something. So my questions are:

  1. Does a high BMI always indicate bad health?

  2. Is it bad to have higher bone density( or high "flesh" density)?

  • You are asking here two different questions, please consider separating them to two different posts, in order to avoid very long answers to this question, and for better organization on the site. – Don_S Jul 26 '18 at 7:19
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    Related: health.stackexchange.com/q/11331 – Chris Rogers Jul 26 '18 at 8:12
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BMI is absolutely NOT a good indicator of health. At least not on its own.

It is made up of two measurements only: height and weight. Height is a stable property, and a person cannot do anything about it (nothing physiological and permanent, at any rate). Body weight, however, is comprised of different types of tissues in the body, most notably fat and muscle tissues (and let us not forget that ~60% of our body weight is water...).

Growth of either type of tissue adds mass to the body, which means that your weight increases by the same amount whether you develop muscles or build fat tissues through overeating (mass is mass for both types of tissues, volume is not). Therefore, it is entirely possible for two people of the same height to have the same weight and therefore the same BMI value, even though one is fat and the other is well-muscled. Your body weight does not tell you if you have more fat than muscle or vice versa. (see also this section in the Wikipedia entry).

Of course, being overweight may lead to adverse health issues, and being fit and physically active is considered protective against such issues (see WHO page about obesity and overweight). The point is that BMI score does not tell you if you are the former or the latter, it only gives you some estimation of the ratio between your height and weight and therefore should not be used alone for estimation (just like you say your doctor did).

So why do we STILL use BMI in a health-related context?

The main reason is probably that it very convenient and straightforward. Only two easily-measured values, which a person usually knows at any time. Thus, it is very available. This also makes it very popular, in the sense that people can talk about it outside of the medical context (i.e. not only when talking to a healthcare professional). Obviously historical reasons play a small part also.

There are some variations and alternatives to make better use of BMI, see here.

See also this nice article from The Independet about the subject.

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    A high bmi suggests bad health (being overweight will lead to adverse health issues), but a normal-ranged bmi doesn’t suggest that the person is healthy. – Narusan Jul 26 '18 at 7:49
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    @Narusan - The BMI charts fail miserably when confronted with muscular people. I have a body fat percentage in the low double digits and a bmi that says I am bordeline obese. – JohnP Jul 26 '18 at 14:00
  • Thanks for pointing that out. I guess for a large BMI it's either high muscle mass or high fat (or general largeness as Jan points out). But those are exemptions of the rule (although training spreads more and more, obesity is still the prevalent cause for a high bmi, at least in my limited experience). The rule of thumb - too large a BMI = unhealthy - is valid as a rule of thumb. As always with medicine, there are edge cases and exemptions, so use with caution – Narusan Jul 26 '18 at 14:42
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    @Narusan Nah, BMI is a lazy, scientifically unsound measure. It's ridiculous and should be abandoned. – Carey Gregory Jul 27 '18 at 4:15
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In short: You can have a high BMI (weight in kg/height in m squared) due to:

  • Excessive fat
  • Large muscle mass developed by training
  • "Large frame size," which is genetic, and includes thick bones, relatively lot of muscle mass ad large internal organs. With this large frame, you can have a high BMI without excessive fat, but for BMI as high as 30.4, you would very likely have some excessive fat. However, if the fat is evenly distributed, it may not make you look very fat.

What's considered normal body weight, depends on the body frame size. According to this height/weight chart, for a 6'0" high man with a small frame, 149 pounds can be normal and for one with a large frame 188 pounds can be normal.

Body frame size is genetically determined and is associated with the bone thickness (not bone density). Body frame size can be evaluated from your height and wrist circumference.

BMI 30.4 is not in a normal range for any frame, so the excessive weight must come from excessive fat (unless you have developed a lot of muscles by training). There are different types of obesity - if fat is evenly distributed through the body, you, again, won't look that obese as if fat is mainly in your belly (abdominal obesity, apple type) or around the buttocks and thighs (pear type).

Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have a negative effect on health. According to CDC.gov, people who have obesity, compared to those with a normal or healthy weight, are at increased risk for many serious diseases and health conditions...including high blood pressure, coronary heart disease, diabetes type 2, etc.

According to various study reviews, abdominal obesity is associated with significantly higher risk of various diseases than other types of obesity.

  • This completely ignores muscle mass vs. fat mass. – Carey Gregory Jul 27 '18 at 4:18
  • Muscle mass vs fat mass has been covered in another answer, so I'm not going to repeat it. Here I try to answer how someone can have a high BMI but still not look obese as the OP states. – Jan Jul 27 '18 at 7:37

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