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Dieting Mathematics

Answered on August 19, 2014
Created May 14, 2012 at 5:09 PM

My math skills are laughable. I'm currently 140 pounds at 12% bodyfat. I'm going to do a protein sparing modified fast for two weeks (ala Lyle McDonald's RFL). For those two weeks, I will be on a 1,200 calorie deficit.

2 weeks = 16,800 calorie deficit 1 pound = 3,500 calories Total projected fat loss = 4.8 pounds New weight = 135.2 pounds.

How would I estimate my new bodyfat percentage?

35b2cb4d450e5288895c255dfdfff35d

(5828)

on May 14, 2012
at 05:26 PM

Oops. It's 12 pounds of fat you'd have (135.2-123.2 = 12.0). 12 pounds / 135.2 = 8.9%. Sorry for the error.

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4 Answers

best answer

1
35b2cb4d450e5288895c255dfdfff35d

(5828)

on May 14, 2012
at 05:15 PM

IF all 4.8 pounds of weight loss were fat, and that's a huge "if," then at 135.2 pounds after the two weeks, if you still had the same lean mass as before (88% of 140 pounds = 123.2 pounds) then you'd have 13 pounds of fat. 13 pounds / 135.2 = 9.6%.

35b2cb4d450e5288895c255dfdfff35d

(5828)

on May 14, 2012
at 05:26 PM

Oops. It's 12 pounds of fat you'd have (135.2-123.2 = 12.0). 12 pounds / 135.2 = 8.9%. Sorry for the error.

4
870fdea50f2a9f1cd2890c8e22549300

(2056)

on May 14, 2012
at 05:14 PM

I don't think you can predict with any certainty what percentage of your overall weight loss will be fat versus muscle tissue versus water. You can't solve the equation, therefore, because that variable is missing. Were you assuming that your loss would be 100% fat? I don't think this is a valid assumption.

Others will correct me if I'm wrong.

1
Dc6407193ba441d1438f6f0c06af872b

on May 14, 2012
at 06:40 PM

I just wouldn't make these assumptions, even to keep it all simple. You don't know what'll happen to your metabolism, muscle mass, etc. It would be a cool experiment, though, to do this experiment and report back on your results via an edit. N=1, so it wouldn't necessarily apply to anybody else, but cool anyway. Of course, that presupposes you have some sort of accurate way to measure body fat, which is another highly dubious assumption. Maybe a waist measurement or something might be the way to go ...

0
41088c15a77277f4d28f5d918c04da20

on May 14, 2012
at 05:23 PM

This is obviously assuming a perfect scenario. I just wanted to get an estimate. Thank you!

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