I have convinced myself that one of the keys to health is not the BMI, as some nutritionists would have us use, but percentage of body fat. Having said that, do any of you Dopers have any experience with scales or other devices that measure body fat electronically? Any recommendations?
I have one of the Tanita scales - I don’t recall the model number, but it measures pounds down to 1/10th and body fat to .1%. As far as the body fat percentage, I notice that it fluctuates wildly; much more so than weight does. You can use it to get an idea of your body fat percentage, but it isn’t really useful for tracking and charting. At least not the obsessive kind I had planned. 
I have a Tanita scale, too. If I remember what the owner’s manual says, the reading varies quite a bit throughout the day. The most time when the percentage is most accurate is around 6 pm. But I tend to weigh myself in the morning, just before stepping into the shower, so having to weigh myself a second time in the evening is a bit inconvenient, especially since I have to take off my shoes and socks to do it. But if that’s an inconvenience you can live with, then it’s a useful gadget.
So long as you measure yourself at a consistent time each day, it’s decent. It may not be incredibly accurate, but it seems to be precise–its readings aren’t spread out all over the map at 6 pm each day.
What’s changing your reading is your level of hydration, which varies throughout the day. I’ve got one, and I can lower my body fat percentage by one just by drinking a glass of water. But it is a decent investment.
Since it is measuring resistance, I would assume that foot moisture would effect the reading too. Do you dry your feet before you wiegh?
No, but as long as I consistently don’t dry, that shouldn’t make a difference. My office is not the sort of place where one’s feet get wet.
Another Tanita owner checking in. I use it mainly to detect a relative change in body fat percentage, and I always do this at the end of the day when I’m most hydrated. Of course, the weight that counts is the one in the morning when I’m least hydrated. 
Also have a Tanita and it is rather consistent (first thing in the morning)
however, it is about 10 points higher than the body calipers that they use on me in the gym…
They do both go down and up together - so I do know if I’m losing body fat or gaining body fat, I just am not sure of how much there really was to begin or end with.
We have a Tanita Body Comp Analyzer (TBF - 300 Goal Setter) at the office, and it is important that you use it according to the guidelines.
If you use it correctly, it is very reliable. If you don’t, or if it doesn’t have different settings for standard and athletic types, forget it. Time of day, hydration, etc should be consistent…usually very do-able…read the intstructions. This is a piece of equipment where not controlling the variables will result in greater +/- accuracy.
Overall, it has helped me tremendously, because as I gain muscle (and weight) I want to make sure that my body fat is controlled. If I used only a scale, I could not be certain that I wasn’t gaining fat weight. This way, I am confident that I put on X amount of muscle weight, and I can be confident in my diet and exercise balance.
For the record, here are my last stats from Tuesday:
35 years old, 5’ 10"
BMI = 25.2
fat% = 17.5%
BMR= 7612kj (calories = 1819)
fat mass = 30.8 lb.
FFM= 145 lb
TBW= 106.2 lb
Ideal range = 17-23% body fat
Ideal Fat range = 29.6 - 43.41 lb
Without this analyzer, I would be doing alot of guessing about my diet versus body composition, and I might see weight gain as fat and accidentally cut calories needed for muscle building.
I’m not entirely certain what the practical or scientific difference between BMI and an electronically determined % body fat is. Can you help me out?
The reason I ask: I’m well aware that BMI can be misleading if you are at a fairly low bodyfat, slightly overweight by charts, but can deadlift 800 pounds in your sleep. What are YOU hoping to measure or accomplish?
It’s been a while since the OP, but BMI is a ratio between body weight and height. The same body weight, for the same height, can correspond to many different compositions: it’s the reason why BMI is considered “inapropriate” for quite a range of people, from athletes to pregnant women.
Measuring % body fat is about actual composition. Unlike BMI, it differentiates between a bodybuilder and a fat person of the same weight and height.
James Krieger has an excellent series on the pitfalls of bioelectrical impedance, DEXA, and other methods of body fat measurement:
^ Was just going to post the same thing.