DEXA Body Scan - Shed Fat, Not Weight

2»

Replies

  • PikaKnight
    PikaKnight Posts: 34,971 Member
    edited March 2015
    Really great write up by the ETP group in regards to pros and cons of the different methods of getting body fat estimation if anyone was interested:

    http://www.myfitnesspal.com/topics/show/830595-body-fat-estimation-methods
  • _Terrapin_
    _Terrapin_ Posts: 4,301 Member
    _Terrapin_ wrote: »
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    Are you thinking of BMI? This is one very strange thread.

    Indeed. And being stronger doesn't mean you're building/ keeping muscle.

    How much weight had you lost in total?


    _Terrapin_ wrote: »
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    Are you thinking of BMI? This is one very strange thread.

    Indeed. And being stronger doesn't mean you're building/ keeping muscle.

    How much weight had you lost in total?

    Not sure if this was for me?!? Was it?

  • PikaKnight
    PikaKnight Posts: 34,971 Member
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    How far apart were your scans? During that time, were you eating at a deficit? How large of a deficit? How about your protein macro? What was that set at?

    If you were still in a deficit than eating sufficient protein and strength training helps minimize muscle mass loss, but it doesn't prevent it completely.

    As IronFeline pointed out, as well, gaining strength =/= gaining/retaining muscle mass. You can definitely get much stronger without building additional muscle.
  • EvgeniZyntx
    EvgeniZyntx Posts: 24,208 Member
    Merkavar wrote: »
    I wouldn't mind getting one of these scans. But more when I get closer to my goal weight.

    I hope I'm not losing muscle too much. I do cardio and some strength training and I keep putting my weights up every other week or so, suggests to me I'm gaining a little muscle at least.

    According to my super "accurate" scale I have 30% body fat which if my math is correct, if I was to get to about 15-17% body fat I would be like 90kg which I think is above the healthy weight ranges I see.

    Having a more accurate bf% would let me be more accurate in my goal.

    I don't want to get down to the healthy weight range and find I lost 5-10kg of muscle to do it.

    Whether
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    It's not so much a question of calibration but different machines use different models (2, 3, 4 compartment density models) to carry out calculations. They can be well calibrated and still give slight differences. Always try to use the same machine, set up by the sane technician.
  • beertrollruss
    beertrollruss Posts: 276 Member
    To answer pikaknight's questions, it was nine months in between scans. The scans were at two different places only because the first place was not available. I did eat at a deficit and I was 14 pounds lighter for the second scan. If I were to believe the second scan, I would have lost 4 pounds of fat and 10 pounds of muscle during that time while increasing my lifts 10-25% and consuming an average of 190 grams of protein during that time. I may have accepted losing 10 pounds of fat and 4 pounds of muscle, but not the other way around. A 10 pound difference on my 210 pound body is almost a 5% variability in readings. That's too much variability for me to trust either measurement.
  • brianpperkins
    brianpperkins Posts: 6,124 Member
    To answer pikaknight's questions, it was nine months in between scans. The scans were at two different places only because the first place was not available. I did eat at a deficit and I was 14 pounds lighter for the second scan. If I were to believe the second scan, I would have lost 4 pounds of fat and 10 pounds of muscle during that time while increasing my lifts 10-25% and consuming an average of 190 grams of protein during that time. I may have accepted losing 10 pounds of fat and 4 pounds of muscle, but not the other way around. A 10 pound difference on my 210 pound body is almost a 5% variability in readings. That's too much variability for me to trust either measurement.

    So you have no baseline, just two completely independent measurements. You maximized, rather than minimize, variables.
  • PAV8888
    PAV8888 Posts: 14,303 Member
    Merkavar:

    This is what you get with a DEXA scan: http://www.bodycomp.ca/sample.html

    By the looks of it, if you have a lot of "free" fat, eat sufficient protein for your lean body mass (let's call it a target of at least 0.7 per lb of LBM, with many advocating up to 1g per lb) , lift heavy weights, don't overdo the cardio and maintain a reasonable loss rate of no more than 1% per week (and/or eat at no greater deficit than 20% off your TDEE), you will have done everything you can to "spare" your lean body mass. And you will still lose some!

    Having done it, did it give me any information that I couldn't live without? Given my original fat %, not really.

    However, I found it darn informative and regret that I didn't do my first scan before I started losing weight!

    re: scale based estimates:
    My last scan was 32.8%. Mathematically I can only range between 34% (all subsequent weight loss was LBM) and 30.5% (all subsequent weight loss was fat). My scale has been saying 27% to 25%

    Yes, I do realize that the "gold" standard is fairly silver.
  • Iron_Feline
    Iron_Feline Posts: 10,750 Member
    _Terrapin_ wrote: »
    _Terrapin_ wrote: »
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    Are you thinking of BMI? This is one very strange thread.

    Indeed. And being stronger doesn't mean you're building/ keeping muscle.

    How much weight had you lost in total?


    _Terrapin_ wrote: »
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    Are you thinking of BMI? This is one very strange thread.

    Indeed. And being stronger doesn't mean you're building/ keeping muscle.

    How much weight had you lost in total?

    Not sure if this was for me?!? Was it?

    No sorry. Quote fail
  • _Terrapin_
    _Terrapin_ Posts: 4,301 Member
    _Terrapin_ wrote: »
    _Terrapin_ wrote: »
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    Are you thinking of BMI? This is one very strange thread.

    Indeed. And being stronger doesn't mean you're building/ keeping muscle.

    How much weight had you lost in total?


    _Terrapin_ wrote: »
    I've had 2 DEXA scans after hearing they were the gold standard for body fat. They're not. DEXA scans are very good for bone density which is what they are designed for. DEXA scans are considered reliable for large populations but not reliable for individuals within the population. DEXA scans are also not reliable for tracking body fat changes. In my case, the DEXA scan said I had lost 10 pounds of muscle, even though I lifted weights and got stronger during the whole time in between scans. Unfortunately, there is no gold standard. Like other methods, the machines need to be calibrated. Going forward, I'm not going to worry about a body fat percentage. I'll focus on losing inches in the waist and hips and continue working out and dieting until I'm happy with how I look and feel.

    Are you thinking of BMI? This is one very strange thread.

    Indeed. And being stronger doesn't mean you're building/ keeping muscle.

    How much weight had you lost in total?

    Not sure if this was for me?!? Was it?

    No sorry. Quote fail

    Oh it's okay. I thought you meant the poster who has been lifting for a long time but didn't understand the difference between DEXA and BMI. I think Brian provided a spot on response for the poster.

  • _Terrapin_
    _Terrapin_ Posts: 4,301 Member
    To answer pikaknight's questions, it was nine months in between scans. The scans were at two different places only because the first place was not available. I did eat at a deficit and I was 14 pounds lighter for the second scan. If I were to believe the second scan, I would have lost 4 pounds of fat and 10 pounds of muscle during that time while increasing my lifts 10-25% and consuming an average of 190 grams of protein during that time. I may have accepted losing 10 pounds of fat and 4 pounds of muscle, but not the other way around. A 10 pound difference on my 210 pound body is almost a 5% variability in readings. That's too much variability for me to trust either measurement.


    I think this is a good illustration of the 'it isn't accurate, no way this is even close' when in fact two different techs may have used two different set ups at the two different locations. The ego saying 'this can't be right' when in fact you need to choose one scan and repeat the scan at the same locale, use the same tech, and not be surprised when you've lost muscle mass eating in a deficit.
  • yarwell
    yarwell Posts: 10,477 Member
    Mr_Knight wrote: »
    DEXAs aren't that great for body fat measurements. They don't actually measure fat

    only an autopsy can deliver an actual measurement of fat.

  • yopeeps025
    yopeeps025 Posts: 8,680 Member
    OP what have you found for your dissertation in regard to like bod pod and hydrostatic weighing for the gold standard of measuring body fat % if you had?
  • BeckiSwim19
    BeckiSwim19 Posts: 22 Member
    This is all really interesting stuff, thanks for getting so involved everyone!

    Just one quick question, would you say the DEXA scan is worth the money? (basing it on £250 for the scan)
  • yarwell
    yarwell Posts: 10,477 Member
  • PAV8888
    PAV8888 Posts: 14,303 Member
    edited April 2015
    Edit after seeing Yarwell's better pricing!
  • lydiakitten
    lydiakitten Posts: 132 Member
    I had a friend who got a lot of DEXAs done to monitor her muscle/fat, after she'd been taking cortisone and having some chemos done. The medical doctors didn't seem to trust the scans that much, and only used them as one possible clue among others. Indeed, there is a lot of space for error and inaccuracy with DEXA scans, and they do use formulas based on population averages.

    Plus it's expensive. Skinfold calipers have similar error margins and are free at some gyms.

    Still, I maintain that the best way to know how fat or muscly your body is, is touching it, looking at it, testing it, feeling how strong or how squishy you are, comparing throughout a period of time. But that's just an opinion, of course.
This discussion has been closed.