How does hydration affect body fat measurement

National Academy of Sports Medicine. Yes; depending on your method of tracking body fat and lean body mass. Bioelectrical impedance is a method of tracking body fat that occurs by sending a low voltage electrical current through the body.

Your muscle is composed largely of water. Since water is a conductor of electricity, the resistance the electrical signal experiences while traveling through the body will help determine what percentage of your body is fat. If for some reason you are over-hydrated or dehydrated, your results will be impacted. If you have just consumed a sports drink, the increase of fluid and electrolytes in the your system will speed up the electrical current and show a lower body fat than what is actually present.

If you are dehydrated, the current will pass through at a slower rate and show an inflated body fat percentage. On the flip side, it soars through fat-free mass, such as muscle, which contains 70 to 75 percent water.

Flood your body and the device will give you a falsely low fat reading. To get the best results, don't exercise it's dehydrating or sip two hours prior to your analysis, says F.

Xavier Pi-Sunyer, M. Pi-Sunyer explains it's better to pinpoint your body-fat percentage optimally 20 to 30 percent for women ages 20 to 40 at a medical center with underwater weighing. Jason took over an hour to drink his water. As can be expected, the majority of the water's effect is on lean tissue. As you probably know, the DXA scan categorizes all non-bone, and non-fat matter as lean tissue, including blood and other fluids.

By increasing the amount of water in your body, you're effectively increasing your lean tissue amount — and decreasing your body fat percentage. The fat tissue numbers are also changed slightly as water is dispersed throughout the body over the course of an hour, changing the average tissue density.

However — notice that it took an entire gallon of water to drop Jason's body fat percentage by 1 percent. How much is one gallon of water? That means that when you drink just 1 or 2 cups before your scan, the difference in your results should be negligible.