What Chuck Does

Body Weight, Fat %, Hydration %

This is the Tanita BF-681W. This is how I acquire my body weight, fat % and hydration readings. The following is an account on how I believe it works and recommendations for consistent readings.. Disclaimer: This may or may not be entirely factual.

The Tanita scale like most other scales shoots a small current of electricity through your body and depending on the level of resistance, measures a voltage that is then “translated” into a fat% and hydration level. This works because of the basic equation V=IR where V=voltage, I=current, and R=resistance. The current is constant and the resistance is your body, thus providing a variable voltage.

Some people swear by these scales while others think they are horribly inaccurate. Of the people who hate these scales, more than half of them are in denial. When I first stepped on my Tanita I said, “WTF?” when I saw my results.

Source: Bioelectrical Impedance Analysis “weighs” each of the different kinds of tissue in your body. It measures the amount of muscle and other lean tissue, like your organs, and the amount of fat and water in your body. Bioelectrical impedance analysis is based on the conductive and non-conductive properties that exist in biological tissues. Most of the body’s fat-free mass is composed of conductive tissues such as muscle, while fat is part of the non-conductive tissue mass. The volume of these tissues can be estimated from the measurement of the resistance to an applied electric current flowing through the body.

BIA measures the impedance or resistance to the signal as it travels through the water that is found in muscle and fat. The more muscle a person has, the more water their body can hold. The greater the amount of water in a person’s body, the easier it is for the current to pass through it.

Back to the subject at hand. All of the actual measurements and facts above are scientific. It’s all true. The subject of controversy surrounds the algorithms programmed into the scale by Tanita engineers. They take minimal variables then combined with the voltage output, compute a fat percentage and hydration level. What about body type? Mesomorph, ectomorph, endomorph. What about bone structure? Small, medium, and large frames. In addition my friends and I have experienced that the algorithmic outputs are susceptible to variations in hydration levels and pre/post meal weighings. I’ve even read that skin temperature can affect the outputs. I’ve also read that these scales are less accurate for athletes than non-athletes.

Essentially while we applaud the Tanita engineers in attempting to derive true fat readings from these variables, we must also acknowledge the fact that the algorithms are limited in their ability to produce accurate results. That said, the Tanita scale can also be a powerful tool for providing baseline readings and tracking change over time. In order to obtain consistent readings, here’s the best way to weigh yourself:

1. Maximize your hydration levels. I do this by drinking water throughout the day intentionally maximizing water absorption. Don’t forget that sodium is critical for water absorption otherwise you’ll just pee out all your water. By maximizing your hydration levels you essentially make one of the variables constant. Therefore your weight and your fat percentage are no longer “dependent” on your hydration levels.

2. Before dinner. Since you’ll need time to hydrate yourself throughout the day, you’re most likely to be fully hydrated by the evening. Weigh yourself before dinner so the weight of your meal doesn’t throw off your results. Dinner can vary greatly in volume and weight.

3. Before exercising. Exercise makes you dehydrated. Weighing after exercise will skew your results.

4. Wear nothing. You’re just adding weight to the results and clothes usually don’t conduct electricity thus increasing the fat percentage results and lowering your hydration percentage results.

5. Keep a log of results. One snapshot in time offers little in consistency. The output of the scale is all relative, so log your results over time to know what the numbers mean for you.

Thus far I’ve been doing everything except for #2 and #3. I can change #2 but I usually exercise before I get home. Eating dinner is the reason behind the fluctuations in the weight output. Coming home dehydrated from exercise is the reason behind the fluctuations in hydration levels. Both affect the fat output. Eating dinner gives me a small chance of rehydrating, but there usually isn’t much time between getting home and going to bed. So the maximum amount of time difference between two weighings is usually about 3 hours.

All of these considerations make it that much more important to keep track of your results so you have an average and a baseline from which to base your results.