Q: I
would like to know how relevant the BMI is when it comes to muscle
mass. Isn't it true that muscle weighs more than fat? For instance,
when I was in high school, my weight was 140 pounds during a weigh in.
The girl in line behind me, who was visibly heavier than me by
all accounts (I definitely looked slimmer) weighed in at 117 pounds.
Today, I don't care as much about the numbers on the scale but at the
time I was a bit traumatized! People routinely
under-guess my weight by at least twenty pounds.
I am definitely not making excuses, but I wonder
where we draw the line between being truly "overweight" versus not
measuring up to what may be an outdated standard.
Dr. Kasongo: We tend to be very obsessed by our weight and scales and while
this may help you keep track of wieght gain or loss, it isn't telling
you how healthy you are. Because the truth is that some people think
they are overweight, when the amount of fat they have on their bodies
is just fine, while others may carry hidden fat that the scale won't
tell them about. Our bodies are made up of a lot of different kinds of
tissues (plus a lot of water). There is muscle, fat, bone, and
specialized tissue such as is in our various organs. The body fat
percentage is just that –- the percentage of our weight which is made
up of fat. Body fat percentage is similar to terms such as body fat ratio and body composition.
It is important not to confuse BMI with body fat percentage. I get
really irritated when official websites confuse the two. BMI (body mass
index) is a formula based on height and weight. It was developed
because in the general population, it is correlated with body fat.
Women with a BMI of 25 to 29.9 are considered overweight, while women
with a BMI of 30 or more are considered obese. All adults (aged 18
years or older) who have a BMI of 25 or more are considered at risk for
early death and disability from being overweight or obese. These health
risks increase as the BMI rises. And yes, there are danger zones for
fat storage For most women, carrying extra weight around their waists
or middle (with a waist larger than 35 inches) raises health risks more
than carrying extra weight around their hips or thighs. These health
risks include heart disease, diabetes, and cancer.
However, there are groups for whom BMI is not as accurate –- short
women and muscular people, to name two. BMI also varies according to
some ethnic groups (read Black). You weighed more than the girl in high
school that you looked thinner than because muscle does weigh more fat.
And people under guess your weight when you are muscular because muscle
tends to make people look leaner. So for people who are interested in
changing their body composition and not just their weight, knowing
body fat percentage
better than BMI. For example, if you are exercising to build muscle,
which is preferable, knowing your body fat percentage is a good idea.
Also, when losing weight, you want to preserve as much lean body mass
as possible. Multiple websites have calculators that can help you
determine your body fat percentage like
www.lowcarbdiets.about.com. I hope this helps a bit to clear up confusion.
Mana Kasongo, MD
is a board-certified emergency physician as well as a nationally
published writer with expertise in emergency health care issues and
women's health. Email her at anovelistamedia@gmail.com with
your women's health questions. All correspondence will be kept strictly confidential and your name will not be used if your question is selected. The Ask Dr. Kasongo column
is for entertainment purposes only and the recommendations are merely
suggestions. If you have a true concern you should consult your
personal physician.