We have lunch with salad and compare pedometers. One luncher at home has a smart scale that produces body composition statistics. They look very scientific, but are they correct? Can you trust the verdict of the scale – pedometer, the fat percentage is too high, confesses the luncher?
No, and yes. The data is probably incorrect, but you can do something with it.
Smart scales work with electrical bio-impedance. Impedance is a concept from electrical engineering, it refers to the resistance experienced by an electric current in a conductor. In this case, the body is the conductor, the scale sends a little current through the body and measures how much resistance the current encounters. One tissue conducts well, the other poorly. “Fat conducts poorly,” says Peter Clarys, professor in the department of exercise and sports sciences at the Vrije Universiteit Brussel. He conducted research into and with bioimpedance meters. “Fat is hydrophobic, it doesn’t like water. Muscle tissue conducts much better. So there is a rationale behind the measurement method, but whether you can trust the measurements depends on everything.”
For starters, there are many different bioimpedance meters on the market. “Your question is about a regular scale, which probably measures from foot to foot. There are also devices where the power also flows through the hand, so there are four measuring points,” says Clarys. Electricity seeks the shortest path, so with more measuring points you arrive at a more reliable result. The normal scale mainly says something about the lower body. If you only measure at the hands, it mainly says something about the upper body. With four measuring points, measurements are also taken from left hand to right foot, and from left hand to left foot, and so on. “Then streams go in all directions. The measuring points are alternately switched on and off, which is very fast. Good scales also vary with power frequency, so they can also say something about the moisture inside and outside the cells. This creates an accurate picture, we also use these meters for research and in hospitals.”
Not immediately out the door
The foot scale at home can never be that accurate. Software in the scales interprets the limited readings and links them to data about the average man or woman at certain ages, sometimes asking if you’re athletic or a couch potato. Then a statistic comes out. „Home scales are often pleasing appliances, they underestimate the fat percentage,” Clarys says.
But the home scale does not have to leave the house right away. The measurements can be quite useful, especially if you combine them with the occasional more reliable measurement, Clarys believes. “If you measure once or twice a year with an extensive device, and compare which values your less expensive device gives, then you have an indication with which you can continue working.”
Whatever device you use, consistency in the measurement is of great importance. “If you drink a lot beforehand, the percentage of water is higher. If you have just exercised a lot, then there is muscle damage, which affects the amount of water inside and outside the cells,” Clarys says. So standardize. “For example, measuring every morning. Not once in the morning, sometimes in the evening, or then again before and then again after dinner.”