Tanita vs. DexaScan

Yesterday was our Health Fair at work.  Various health related vendors were there, including the company my personal trainer works for, two massage therapists (chair massages--yay!), medical clinics, and the nutritionist we have here on campus (I work at an American university that is part of an educational complex sponsored by the country's royal family).  The nutrionist was very nice and had a lot of free takeaways to share.  One of the things she offered was a body composition analysis using one of those Tanita body comp machines (it looked like this, but I couldn't swear this was the exact model).  I've seen people talk about these kinds of machines on the boards before and while the general consensus seems to be that they're not as precise as some other means of measurement, they're still a good indication of where people stand when it comes to things like body fat and bone density.

Au contraire, mon frere.

At least in my case, the numbers were waaaaay off.  Some of this I know because I just had a DexaScan a month ago.  Some I know just from common sense.

According to Tanita, my bones weigh 2.5kg total.  That comes to about 5-1/2 pounds.  Given that the average person's bones weigh approximately 15% of their total body weight, that number should be upwards of 19 lbs. for me.  Per Dexa, I know my bone density is slightly above the average for women my age, so clearly this number is off by quite a bit.  I showed it to Mark, my trainer, who was working the event, and he burst out laughing.  His comment was, "I'd take those figures with a big pinch of salt."

Given what Tanita said about my fat percentage, I would definitely agree.  According to the machine's measurement, I'm at 16.7% body fat, which is dangerously low for a woman my age (the nutritionist took one look at this and said with a certain measure of concern in her voice, "You need to be eating more!").  Dexa had me at 23% if you include fat in places like my brain and 22% if you focus solely on my torso.  While a month has passed since that scan was done and I've continued to eat under 1,200 calories and work out regularly, there is no way the percentage has dropped that dramatically.

Overall, the machine told me I was underweight.  I'm 5'4" and weigh 129 lbs.  The nutritionist looked at my data, asked me how often I work out (I told her 4-5 times a week for an hour) and calculated that I should be eating 2,400 calories a day.

2,400!

Good grief.

I wanted to post this here because I think there's a danger sometimes in thinking, 'While this tool (any tool) may not be perfect, the information it will give me is better than having nothing.'  I realize not everyone has the money or the ability to have a scan done and I also know that Dexa isn't perfect either (yet according to everything I've read, it seems like the best option for measuring body fat percentage and bone density).  But seeing the variance here made me consider how someone might look at results gotten from a Tanita or similar body composition scale and figure they're only off by a degree (if at all).  At least in my case, they were off by a significant percentage and the advice I got as a result would have positively sabotaged my weight loss efforts.

Hi Karen. Interesting, thanks!  

I had a dexa scan a few months ago.  I didn't realize it told more than bone density. All I was told was normal. I will ask for the details of percentages, that would be cool to know.  

I am also 5' 4" and 132. So almost the same as u.  I am sure I have higher body fat as I don't exercise much, a little Zumba and hand weights, not consistent.   I'm surprised they said u were underweight.  It is right smack in the mid range of normal bmi. 

Hi, Candy.

I had my DexaScan done largely to look at body fat percentage.  The company that did the scan, Dexafit, analyzed bone density too, which was great.  I was in the top 5 percentile for both (for my age group), so all seems to be well.

I had to laugh at the thought of eating 2,400 calories a day--that's crazy!  I was also surprised at the nutritionist's comment that I was underweight.  I'm 4 lbs. from goal and, as you said, smack dab in the middle of the BMI range.  Granted, we know BMI is a flawed measurement (like nearly everything I've posted about, apparently), but still--I'm not wasting away!  Sometimes you just need to use common sense.

Oh, mine was done at my PCPs office and was paid by insurance as a base line bone scan.  So maybe they don't do the fat percentage part.  I will ask, cant hurt.  2400 - we would be eating all day OR eating junk!

It's funny--before searching for options in the States (I was only able to consider that because an unexpected trip home popped up at the last minute), I'd searched for providers here in Qatar.  Several medical clinics had them here, but they only used them for bone density scans.  One of the big issues in this country is places invest in really sophisticated equipment, but they don't have the technicians with the necessary skills to use the machines.  My Medical Officer advised against doing it here, saying she didn't trust the results would be accurate.  DexaFit was located in a nationally ranked gym in Chicago (it's a serious, no frills kind of place where bodybuilders train).  The default report included both the bone info and fat percentage.  The total cost was $100, so I was pleased.

I agree that "close" sometimes isn't "close enough".  Close enough to give yourself a rough idea perhaps, but not scientific enough to make me feel comfortable basing nutritional information on it.

The woman who did my impedance one with the metal mat and the hand grips said that she was told that those things are calibrated for people with more or less normal amounts of bone and muscle and that if they do it on people who are either very tiny or very large they are supposed to let them know that it can be off by quite a bit (so they know that before they pay for it) and they are NOT supposed to give them the same detailed info I got for calories and RMR. 

So if it can be off by so much for people at the extremes, it makes perfect sense that it can be off for other people as well.  Since they used both the mat and the grips at the health fair I was at, and explained that the mat and grips together are more accurate than just a scale (which I have at home) because it gives two points of reference, I have always been skeptical of the scale only method.

In my case, the body fat % I had done via three different methods were all close -- within 2%, and since they were about 6 months apart, that might account for perhaps half of that difference even though my weight is stable -- but the one from my scale was the lowest of the three, so I always take that number and add 1-2% for where I think I really am.  

Lora

I think you're right--having two data points (the hands and feet) has got to make the information more accurate.  At least, that's what common sense would suggest. 

I also think it's smart to get info from various sources and then see what that tells you.  I was just so shocked to see things like the weight of my bones recorded so very inaccurately.  I could easily see someone being given that info and then panicking, thinking, 'This was measured scientifically, so it's got to be right.'  Clearly this is not an exact science. 

Interesting... I have one of the Tanita models that I bought in a moment of weakness during a weight loss stall.  My percentages were actually pretty darn close to what one would think - and it has been interesting to see how the fat percentage drops when my weight is less cooperative (I lift weights in addition to cardio).  I will certainly keep your warnings in mind - it is never a good idea to base your behavior on one isolated data point!

I think all of us are curious about what's happening to our bodies when we're post-surgery.  I know I am!  :-)  I was just so surprised by how inaccurate the information was.  I completely understand their being a variance of a degree or two, but this was something I could tell was wrong (at least in certain categories) without even consulting another set of data.

No way should I be eating 2,400 calories!  :-)

I just stood on that same thing tonight at a health fair at my surgical weight loss center. The lady gave me the printout of everything. I was surprised that it could tell me how much my organs weigh. Strange. I remember she explained how much of my body was made up of water. I told her that I feel like water is coming out of me everywhere as I prepare for WLS. She laughed. I know water is a good thing and I really don't mind it at all because I know it is so necessary, but I am going to wear a hole in the carpet running back and forth to pee every day.  lol 

I found it odd that she said I should not pay attention to BMI. She said a normal BMI can be unhealthy for a surgical weight loss patient.