DEXA scan for fat composition accurate?

[big booty]

Has anyone had a DEXA scan done? Useful? Accurate? What sort of dose rate does one receive?

[Baalzamon]

Should look at what happened to Jimmy Moore before and 2 dexa scans after 17 and 12 days of fasting

[madmacca]

In terms of decreasing orders of accuracy in measuring body fat and lean mass composition, you have:

1. Underwater weighing
2. Skinfold calipers (in the hands of a trained operator - amateurs can mess up badly).
3. DEXA scans
4. Bathroom BF scales
5. Online BF calculators

[big booty]

Thanks guys. Im assuming that underwater weighing must work on some sort of Archimedes principle of water displacement and buoyancy? It would give you a total fat content but Im assuming wouldn't tell you where that fat was located throughout the body?

Baalzamon do you have the link for Jimmy More and his DEXA scan?

[bigfriendlyvegan]

Here's a water testing setup so you get an idea of what it is.

https://www.youtube.com/watch?v=1oWcpweTuXs

[big booty]

Thanks BFV. Well I sucked at determining the BF% of those volunteers in the video. It then occurred to me that even the percentage is really quite meaningless. You really need to know where the fat is located. Also here's a slight aside. Lets say I weigh 75kg and have 15kg of fat. My BF% = 20% I go to the gym and bulk up. I now weigh 80kg Lets assume Ive lost no BF and its still 15kg worth. My BF% = 18.75%. Am I any better off with regards the BF% Im carrying? Still got the same total as before by my % has gone down.

[TheShadow]

The water tank was always the only truly accurate way to check body fat, since decades ago. It must be related to density, I guess. A combination of weight and the volume of space your body displaces. Seems obvious enough, given muscle weighs more than fat.

I really have to question its significance however, or it's worth as an indicator of an optimum power to weight ratio that you can theoretically achieve at a certain weight. I think you learn that best yourself by riding, and experimenting (within reason) with various body weights.

Afaik, you lose fat first off your tricep area, and upper back, and face. Abdominal fat is slower to go and last to go? If you have no love handles left - I mean if you're under age 40 and you can barely scrape together a tiny fold of skin on the side of your waist - there's probably not a huge benefit going lighter than that unless you're in you're in the top 10 at the TDF and you're trying to peak for the hardest Alps stages. I mean, maybe it would help, but there are probably other performance issues that are more beneficial to concentrate on.

In fact, my non-medical opinion is that I suspect going below a 'pinchable amount of waistline', you're just increasing the risk of getting something like chronic fatigue syndrome, or one of those semi-related auto-immune diseases. Or simply getting really tired, or picking up colds and flu too easily.

And I also have to wonder about stuff like bone density issues as you age, which I notice the water-tank guy in the video mentioned. I think retired Pro Chris Boardman has osteoporosis and I can't help but wonder if that is related to spending too many years at very low body fat percentage......or if that is due to some other kind of "medical" issue related to whatever it was his training preparation involved. He doesn't seem to be the only former Pro with hard to understand health issues.

[big booty]

Ive definitely got enough to pinch around the waist. 55 y o.

Ive had one cold in three years and I have three kids that always bring stuff home from school/uni My wife thinks Im crazy, cold showers summer or winter. Summer isn't too bad, winter is bloody hard work.

[bobbythebrit]

I'm just about to graduate from exercise science and DEXA is pretty much the gold standard in terms of body composition measurements. Underwater weighing is great at overall measurements of body comp but DEXA is able to identify how much fat mass is where etc.

[RhapsodyX]

I'm just about to graduate from exercise science and DEXA is pretty much the gold standard in terms of body composition measurements. Underwater weighing is great at overall measurements of body comp but DEXA is able to identify how much fat mass is where etc.

Agree, but variations between machines and modes mix things up (yes - there is published research to back this up). As long as you use the same machine, the error rate should be low and (from memory) it's been shown to be up to 6% for fat mass, and that would only have been valid for one specific DEXA machine. 6% just for fat mass... I can live with that in terms of repeatability.

[madmacca]

I'm just about to graduate from exercise science and DEXA is pretty much the gold standard in terms of body composition measurements. Underwater weighing is great at overall measurements of body comp but DEXA is able to identify how much fat mass is where etc.

While there is some evidence of health risks based on where you tend to store fat ("apples" v "pears"), in terms of actionability, there isn't a whole lot of benefit to knowing where fat is being stored (other than reducing overall body fat). You can't spot reduce.

[Calvin27]

While there is some evidence of health risks based on where you tend to store fat ("apples" v "pears"), in terms of actionability, there isn't a whole lot of benefit to knowing where fat is being stored (other than reducing overall body fat). You can't spot reduce.

Most accurate would be a series of MRI sections - but this would cost a bomb. When I got my MRI done, I was amazed how much fat my knees could possibly store!

Anyway on where fat is stored and spot reduction. I have a mate who gets fat often and he stores it all around his chest and arms. He actually looks buffed because of it. Amazing.

[ValleyForge]

You can't spot reduce.

Except with liposuction, cool sculpting or surgery.

[bobbythebrit]

Agree, but variations between machines and modes mix things up (yes - there is published research to back this up). As long as you use the same machine, the error rate should be low and (from memory) it's been shown to be up to 6% for fat mass, and that would only have been valid for one specific DEXA machine. 6% just for fat mass... I can live with that in terms of repeatability.

Yeah 6% is pretty bloody accurate for something so intricate, especially compared with methods such as skin folds etc.

[bobbythebrit]

While there is some evidence of health risks based on where you tend to store fat ("apples" v "pears"), in terms of actionability, there isn't a whole lot of benefit to knowing where fat is being stored (other than reducing overall body fat). You can't spot reduce.

There isn't but as you said, if you know the fat is sitting around your abdominal area, you know it's time to do something about it. The biggest problem is that isn't much research at all that has shown that exercise (pretty much in any form) makes you lose weight as a lone strategy.