How accurate are bathroom scales that display body fat and do low carb diets effect this?

Most bathroom scales that provide body fat estimates do so using BIA (bio-electrical impedance analysis). The electrical impedance of body tissues is measured, which provides an estimate of total body water (TBW). Fat-free mass (FFM) and body fat is derived from TBW. Weight, height, gender and age are also required for this calculation.

The NIH found that body fat estimates using BIA can vary as widely as 10% depending on hydration status, consumption of food and beverages, ambient air and skin temperature, recent physical activity and the calculation used (http://consensus.nih.gov/ta/015/015_intro.htm)

Low carbohydrate diets have a diuretic effect. Water consumption is essential to combat dehydration.

I would seem that, given the above, low carbohydrate diets effect the accuracy of body fat scales and that any reading is more likely to be useful in a comparative sense from one reading to the next rather than as an absolute determination of body fat. In addition, the relative readings would only be comparable if taken under the same conditions, e.g. Time of day, state of hydration & meals, recent exercise, rest etc.

What are people's experience with body fat scales?

I have the Tanita BF682, a $90 body fat scale that's accurate to the .1%.

In the 2 months I have been using it, I have found it to be very accurate, sometimes too accurate. I have found the best time to measure my body fat is when I wake up in the morning. The % may fluctuate, but over time the results are obvious.

My results looked like this:

Week 1 (Varied between 39% and 42%)
Week 2 (Varied between 37% and 40%)
Week 3 (Varied between 35% and 38%)
...
Week 8 (Varied between 28.0% and 28.9%)

It has seemed that the lower in weight I get, the more accurate the readings get. However, the net result was obvious. I used MS Excel to make a simple graph of it and though it jumped up and down, the general trend was plain.

Using the numbers, I graphed my body fat vs my lean weight and its nice to see that not only am I dropping weight, but my lean mass is increasing as well. That's pushed my goal weight up from 220 to 225.

Yes, this is why I ask.

My goal was 183 as that's what I was 15 years ago when in top shape.

I have gone from 235 to 209 but stopped there for 6 weeks. I am doing a lot of exercise and now weights.

Ultimately, my goal is really 15-18% body fat. It would be nice to see at least this number coming down even if my weight is not. It may lead me to rethink my goal.

I have the tantia and think it registeres too high most of the time. I also don't think it is accurate.

I weighed and measured body fat one night. Then I went and watched a video having only water. When I weighed and checked again on a lark, I found I had gone down a pound but up 2% body fat. I dobt watching a movie and drinking water really put on 2% body fat. It will also fluctuate depending onhow long it's been since I had dinner. I have noticed though since my body fat has gotten lower the flucuations aren't as wild.

I heard the Tantia, is acually bad at measuring. I read a lot on it on another site because I was going to buy one. Opted not too once I read the reviews. Stuck with a regular $30 scale! LOL

Getting on the scale one time and looking at the body fat number is not the way to do it The optimum way is to check your body fat each night (night they say gives the truest reading for body fat unlike weight which you get in the morning) and jot down the number. Do this for one month then divide by the number of days in that month. That will give you your average body fat. Hope this helps.

Tornado, all diets have a diuretic affect. In The beginning of a diet, the body rids itself of excess water.I find that keeping my body replenished with electolytes outweigh my risk of dehydration. We should all consume a healthy amount of water for optimal health. I feel that the diurectic argument, that is often debated regarding low carb diets, is misleading.

If you really want to know your body fat check with your local University. The local University here does the water submersion body fat % readings for $20. Here soon I am going to get one done and then work my butt off for 6 months, then have one done again.