Welcome to another Medical Minutes. Today, I’m going to spend a few minutes talking about how to measure body fat during a weight loss program. There are several ways that are commonly used to measure body fat in a medical clinic. There’s one way called body impedance that’s very standardized and reproducible and easily done. You can even measure body fat on some home scales. It’s just often a little less accurate or a little less precise. The methodology used by most weight loss physicians, as well as in our clinic, is called body impedance. In body impedance, you stand barefoot on a scale with a plate. Your feet go on the plate and a very low electric current that you can’t feel at all goes up one leg through your lower abdomen and down the other. Through that and some sophisticated formulas, the scale has been shown to pretty accurately and precisely measure body fat.
Let’s spend a couple of minutes talking about patients I have seen in the clinic in the past and what I was able to learn by measuring their body fat on a body impedance scale. So, this is a blown-up version of the data we get from our Tanita scale. If you see, there’s a lot of numbers on it. I always like to add two lines that makes it easier to explain what I’m looking at. So, this is the first line, and this is the second line. If we look at the numbers above the first line, first it shows that it’s a standard body type and she is a female, age 67. Height is five feet, five and a half inches and her weight is 177.5 pounds. The scale then calculates her body mass index, which is 29.1. For reference, people with a body mass index over 30, have obesity and people with a body mass index under 30, but over 25 are overweight.
The next number on there is BMR or basal metabolic rate. BMR is the amount of calories you would burn if you laid in bed for 24 hours at rest and didn’t burn any extra calories. Didn’t go to the bathroom, didn’t get up and get a drink of water. Just laid there still. So, it’s your resting metabolism. In Europe, they use kilojoules. So, it’s 5,951 kilojoules, but in the U.S., we use calories, so we see her basal metabolic rate is 1,422 or 1,422 kilocalories, which are the calories we normally think of. In the clinic, we typically see numbers between 1100 and 1400 for most women.
The last value above the line is impedance. Impedance is what the scale is actually measuring. When you take all the numbers above the line and put it into a calculation, then you get the next four numbers, which are the really important numbers and the thing that this scale can do that other scales can’t. So, the first one on here is fat percentage. Her fat percentage is 41.6%. So, of her body weight, 41.6% of it is fat, and the rest is not fat. If you were to take that same number or that same value of fat and put it into a pound number, if we were able to take the fat out of her body, weigh it separately, which we can’t do, she would have 74 pounds of fat.
So, the first question is that sounds like a really big number, and then you look down to desirable range, which is the third area. And we see that her fat mass should be somewhere between 32.5 and 58 pounds. So, yes, she does have too much fat on her body, but it should not be zero. It should be 58 pounds or less. The third number in this category is free fat mass or FFM. FFM comes out to be five different values. The first factor that makes up FFM is body water, which 73.5% of her 103 pounds of free fat mass is water. The second would be muscle. The third would be bone. The fourth is clothing. And the fifth is if you’re constipated, constipation. If you take your free fat mass, which is everything but fat, plus your fat mass, which is 74, and add them together, you get your total body weight of 177.5 pounds.
The last section, again, as we started to talk about, is there a desirable range? Fat between 24 and 36% and fat mass somewhere between 32.5 and 58 pounds. In our clinic, we tend to do the Tanita test every single time you come in the clinic and our scale and electronic medical record will compare last week versus this week to make sure the weight that you are losing is predominantly fat over muscle and other things as well as if you happen to be up in water, for whatever reason, that we know that you’re up in water and not up in fat. Thanks for being here. I’ll see you next week.
