Thursday, February 16, 2006

Real Weight Loss Science part 3

Real Weight Loss Science part 3

When you're learning about something new, it's easy to feel overwhelmed by the sheer amount of relevant information available. This informative article should help you focus on the central points.

The only way to keep up with the latest about weight loss is to constantly stay on the lookout for new information. If you read everything you find about weight loss, it won't take long for you to become an influential authority.

Calculating Your Weight Loss Goals
Once you know your body fat percentage (BF%), you can then calculate how much fat mass you have, and how much you need to lose based on what a healthy BF% is for you. This can help you determine how to achieve healthy weight loss that doesn’t put your body’s health at risk.
Let’s use an example of a woman in her 20’s who weighs 160 pounds and has 35% body fat. She wants to reduce her body fat to 22% to get into the healthy range for body fat percent for a female her age. Let’s calculate how much weight she needs to lose:

1. To calculate how much fat mass she has, we need to take her weight and multiply it by 35%:
a. 160 lbs x 0.35 = 56 lbs

2. Now that we know that 56 lbs of her body mass are made up of fat mass, we can find out how much fat-free mass, or lean mass, she has. Fat-free mass includes: muscles, bones, tissues and basically anything that doesn’t include fat.
a. 160 lbs - 56 lbs = 104 lbs

You may not consider everything you just read to be crucial information about weight loss. But don't be surprised if you find yourself recalling and using this very information in the next few days.

Those of you not familiar with the latest on fat loss now have at least a basic understanding. But there's more to come.

3. Now that we know that 104 lbs of her frame are made up of fat-free mass, which is body weight she does NOT want to lose, we can figure out how many pounds of fat mass she needs to achieve 22% body fat:
a. 104 lbs x 0.22 = 23 lbs
b. 104 lbs + 23 lbs = 127 lbs

4. We have now determined her healthy weight goal, which is 127 lbs. So, to achieve this weight, she will need to lose:
a. 160 lbs - 127 lbs = 33 lbs

Therefore, this woman needs to lose 33 lbs of purely body fat in order to reach her healthy weight goal of 127 lbs and 22% body fat.

Once you’ve determined your body fat percentage, by using any of the methods we talked about, you can then use that number to calculate exactly how much weight you need to lose in order to reach a healthy weigh and healthy body fat percent.

So now you know a little bit more about weight loss. Even if you don't know everything, you've done something worthwhile: you've expanded your knowledge.

Sometimes it's tough to sort out all the details related to this subject, but I'm positive you'll have no trouble making sense of the information presented above.

Kevin Newman
Weight Loss


Kevin said...

Great series

Detector said...

Hello Kevin.
First let me say that I like your blog and find the information useful, but I have to disagree with you on this method for calculating weight loss goals. The problem is that instead of calculating % body fat based on current weight, you are calculating it based on % of lean body mass. Using your example, you are not calculating 22% body fat on the current weight, but are calculating it based on 22% of 104 pounds. This method will return too low a value. You can prove this to yourself by simply using your example again, but calculating her actual body fat percentage at the weight you list as a goal weight:
127 lbs x 0.22 = ~28 lbs
Add this to your lean body mass of 104 and you get 132.

Something’s obviously amiss.

You can see this even clearer if you look at it another way. If you calculate fat weight divided by lean weight, the result is the proportion of body fat. Thus:
56 / 160 = .35
So, a female with a LBM of 104 that weighs 127 has 23 pounds of body fat (127 – 104). Thus:
23 / 127 = .18
In other words, she has a BF% of 18%, not the 22% you stated. As 18% is probably too low, this seems problematic. In reality, 134 would be a better target because this works out to be:
30 / 134 = .22

The fundamental problem is that you were calculating 22% of 104 and you need to calculate 22% of the current weight. This is easy to say, but there is no easy way to fix your formulas. I’ve thought about this and I can think of now way to formulate this percentage without knowing the current weight. Conversely, I can’t calculate the weight without knowing the percentage. Thus, since both of these are unknowns, exact measures simply won’t work.

All that said, I do have a workaround. Here is the basic formula:

(1 – Current Body Fat - as proportion) * Current Weight = Lean Body Mass
Predicted Weight – Lean Body Mass = Predicted Fat
Predicted Fat / Predicted Weight = %Predicted Body Fat (as proportion)

What this means is that one has to make an educated guess as to the proper weight (predicted weight in the formula). Then it becomes possible to figure out is that weight is acceptable based on its corresponding % body fat.

Let me give you an example: Male subject, 220 pounds, 30% body fat:
(1 - .30) * 220 = 154 (This is the lean body mass)
180 – 154 = 26 pounds of fat at 180 pounds
26 / 180 = 14.4% body fat, a number within the acceptable range regardless of age.

Had the % body fat been outside the acceptable range, simply adjust the target weight and calculate again.

Kevin said...

You are correct Detector in your mathematical calculations. I should have expressed it a bit differently. I should have expressed it as you are a X lbs with Y% body fat and you want to reach Z% body fat. (Y-Z)*X=# of lbs of body fat you want to lose.

Given that equation and the example of:

180 Lb Male 12% Body Fat wants to reach 6% Body Fat

The equation would then be
180*.12=21.6 fat
180-21.6=158.4 lbm(lean body mass)
(.12-.06)180=10.8 fat to lose
169.2 *.06=10.152 lb fat
169.2-10.152=159.048 lbm

This is within one pound of starting lean body mass and actually shows a slight increase in lbm which is normal if the fat is taken off at the rate of about 1 pound a week which is easily doable.

I think one of the biggest problems is that people try to discard the fat too fast and end up losing lbm as well which sort of defeats the purpose because you end up with a slower metabolism when you want a faster metabolism to burn the fat off as energy.

This all ties into my next article of determining your TDEE or Total Daily Energy Expenditure.

Thanks for reading and keeping me on my toes.


Detector said...

Kevin, this issue really intrigued me, so I spent some time thinking about how I could address this issue programatically. As a result, I have created a web site that can calculate an appropriate weight based on LBM and any desired %BF. If you’re interested, take a look at it here: