| Total body weight can be broken down into compartments
according to the type of tissue and how each compartment functions.
We use BIA to estimate how much fat-free mass and fat mass are in the
body. Equations were published[1]
to help us break fat-free mass down further into two sub-compartments:
body cell mass (BCM) and extracellular mass (ECM or ECT). This helps
us to better characterize what is going on in the body at any point in
time, especially if you have more than one reading to compare results.
You will be forever confused about BIA until you know what each of these
compartments represents.
Definitions, please!
First and foremost, the body needs enough body cell mass,
which “jargonites” often refer to as simply BCM. This compartment is primarily
muscle and organ tissues.
These tissues are greedy for calories and use nearly all
the calories you expend everyday. So, the more BCM you have, the more calories
you need to sustain this important compartment. It has long been known that
when your BCM drops below a good level, you are more likely to get sick, feel
fatigued, or even die! Keeping your body running at 100% requires 100% or
better than what is expected for that compartment. At 95% of the expected
level, there is likely to be some functional compromise. Below that can
get you into hot water fast. And, at about 55% of this expected level,
regardless of how you got there, you and every other human in the world will
die… just not enough of this stuff to keep you going.
The other sub-compartment of fat-free mass is extracellular
tissue a.k.a. ECM or ECT. Yep, it’s fat-free, but it has entirely different
functions associated with it. This stuff includes the bone, collagen, and fluid
tissues around the cells.
It doesn’t use up much in the way of calories, but it is
important to be there in full capacity and volume so that the other body parts
work.
And, finally, fat (the “other” compartment we have so many misgivings
about). Fat tissue can be subcutaneous (stored type) and can also
contribute to small amounts of metabolism calorie use as functional and
essential fat. You definitely need this stuff… don’t shortchange
yourself! Sex hormones and insulin sensitivity can be compromised
if you have too little.
Here, like in other circumstances, men and women are
different! Men tend to have more muscle tissue and women have more fat tissue.
Trust me on this, that is the way it is supposed to be and our hormonal
homeostasis counts on it!
Here is how it shakes out:
If you are a man at a good weight and in pretty good
shape:
40-45% should be BCM
40-45% should be ECM
10-20% should be fat
If you are a woman at a good weight and in pretty good
shape:
30-40% should be BCM
35-45% should be ECM
20-30% should be fat
Obviously, if you are an athlete, more emphasis may be on
BCM and less may be on fat. Still, you don’t want to go much below optimal fat
levels or you may experience some problems.
[Okay, that is good for Mr. And Ms. Optimal, but what about
the rest of us??]
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