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Body Fat %- am I doing my math correctly?

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  • Body Fat %- am I doing my math correctly?

    So the other day, I stepped on a friend's scale that supposedly measures body fat %. It said that 34% of my weight (135lb) is body fat. 135X.34=47.5 lb! Is that right? So, if I wanted to get down to only 15% body fat, I would have to drop 35 lbs, right? Here's my math:
    135-47.5=87.5 (lean weight?)
    87.5*1.15=100.625 (weight with added 15% body fat?)

    Okay, so i know this doesn't take into consideration an increase in weight due to increased muscle mass. But as far as muscle mass goes, I'm really not that skinny now. So I'm thinking that my math logic must be off. Can anyone help?
    my primal journal:
    http://www.marksdailyapple.com/forum...Primal-Journal

  • #2
    Your maths is good. I just wouldn't believe that a scale could measure my body fat percentage
    Four years Primal with influences from Jaminet & Shanahan and a focus on being anti-inflammatory. Using Primal to treat CVD and prevent stents from blocking free of drugs.

    Eat creatures nose-to-tail (animal, fowl, fish, crustacea, molluscs), a large variety of vegetables (raw, cooked and fermented, including safe starches), dairy (cheese & yoghurt), occasional fruit, cocoa, turmeric & red wine

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    • #3
      thanks. I think that the scale must be wrong. If I weighed just 100 lbs, I would have a BMI of 17.2. My goal weight is around 115-120, though I'm more concerned about how I look and feel than what I weigh.
      my primal journal:
      http://www.marksdailyapple.com/forum...Primal-Journal

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      • #4
        I wouldn't trust a scale to give anything like an accurate measurement of bf percentage. If you can get booked in a bod pod you can get a very accurate reading, but if you can find a measuring tape, this is about the best you could do. Hope it helps. Your scale might be reading high so, you just might like this better anyway.

        http://www.scientificpsychic.com/fitness/diet.html
        http://www.facebook.com/daemonized

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        • #5
          A scale CANNOT measure bf. At best it can do some bullshit like the BMI (which is mostly meaningless anyway).
          A steak a day keeps the doctor away

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          • #6
            Hoooowww taaaaalllll aaaare yoooouuuuu
            You lousy kids! Get off my savannah!

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            • #7
              A scale can measure body fat percentage by using impedance, which is only accurate if you are well hydrated
              Meghan

              My MDA journal

              Primal Ponderings- my blog- finally added some food pron :P

              And best of all my Body Fat Makeover!!

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              • #8
                Tanita has a scale which says it can measure bodyfat percentage. It does this by impedance. Bone and muscle (LBM) have low impedance, fat has higher impedance. Problem is, the scale only measures the current flow from one leg to the other, and does not account for hydration. Your BF% in your upper body will not betaken into account with a Tanita scale.

                If you carry a lot of your fat in your hips/thighs---the bf% it gives will not be accurate. Also...if you're a little dehydrated, as in the morning...your bf% can read 7-10% higher, than the rest of the day. Just sayin'....

                ETA: Take your weight in the morning---take your bf% in the afternoon.

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                • #9
                  I've got a salter bioimpedance scale. I know its a load of rubbish, but it is nice to have something to go on if you are weighing yourself regularly (eg, my bf has dropped by 3.5% since I got it 6 months ago) Interesting kuno about it being higher in the morning, cause that is when I measure most the time, ie after having a cuppa tea and going to the loo and then having a shower. When I got weighed on the gym Tanita scales the amount was MUUUUUUUUUCH higher. Hence I dont really take a hell of a lot of notice of any of them I just want to look smoking in a bikini some time and I dont need a body fat measurement to tell me that I look good (assuming that will happen sometime)

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                  • #10
                    With the scales, as long as you use the same one each time and at the same time of day it will give you an idea of whether or not you are losing BF. No, it won't be 100% accurate, but it is easy to do We had one that was pretty close to being accurate. I went into a Bod Pod and then the next day used our scale (after the shower so there is better contact with the electrodes) the scale was just a little over 1% off. That was close enough for me to know I was getting a fairly good idea of my BF%.

                    The one we had also measured hydration levels, so if my hydration level was low and my BF% was higher than normal, I knew why. It was nice until the kids got a little primal in the bath tub and flooded the floor, now it doesn't work at all...lol
                    Meghan

                    My MDA journal

                    Primal Ponderings- my blog- finally added some food pron :P

                    And best of all my Body Fat Makeover!!

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                    • #11
                      I wanted to say too though, that your math may be correct, but even if you lost no more body fat and gained lean muscle mass, you BF% would decrease. So if you exercise and weight train you will decrease your BF% and may not need to lose that much fat. So you could weigh say, 120 and be closer to a BF% you like because you increase your lean mass.

                      It would be a bad idea to focus only on losing fat if you want to be 15% BF, you would be so scrawny and might look like one of our banana friends.
                      Meghan

                      My MDA journal

                      Primal Ponderings- my blog- finally added some food pron :P

                      And best of all my Body Fat Makeover!!

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                      • #12
                        My scale measures bodyfat and I use it more as a measure for hydration...if I'm dehydrated, it comes in anywhere from 42-47%. When I'm hydrated, it shows 38-39%. I've been measured and it is just under 28%.
                        Lesson learned - scale bodyfat measurement is a joke.

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                        • #13
                          Originally posted by Saoirse View Post
                          Here's my math:
                          135-47.5=87.5 (lean weight?)
                          87.5*1.15=100.625 (weight with added 15% body fat?)
                          No, actually the math is wrong.

                          100.625 - 87.5 = 13.125 pounds of fat. 13.125 / 100.625 = 13% fat. Not hugely off, but the math is wrong. You took 15% of 87.5 (lean weight), not 15% of total weight.

                          What you need is 87.5 / 0.85 = 102.94 total pounds
                          102.94 - 87.5 = 15.44 pounds fat
                          15.44 / 102.94 = 15%

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                          • #14
                            @avacado

                            You beat me to it.



                            Unless you have paid over $500 for your scale it will not be very accurate. My Costco special impedance scale will not budge past 21.5% even though calipers, tape, better impedance scales have me around 11%. I can't even use it for trends. I suggest a pair of calipers and measuring the skinfold an inch above your hip bone for trends.
                            Don't be a paleotard...

                            http://www.bodyrecomposition.com/nut...oxidation.html

                            http://www.bodyrecomposition.com/nut...torage-qa.html

                            http://www.bodyrecomposition.com/fat...rn-fat-qa.html

                            http://www.bodyrecomposition.com/nut...-you-need.html

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                            • #15
                              THIS is the most accurate way to measure Body Fat % without using calipers
                              ===============================================
                              http://www.free-body-fat-calculator.com/
                              http://lowcarbdiets.about.com/librar...yfatcharts.htm

                              Also THIS is the best way to measure Body Mass Index & your ideal weight target
                              =================================================
                              http://www.halls.md/body-mass-index/av.htm

                              PS) My weight just hit another 35 year low today, 218 lbs on my way to my ideal weight of 175 lbs.
                              Many Thanks the the Primal Blueprint.

                              Best to all,
                              Grizz

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