Do you think that “body fat percentage fluctuates every time you measure it, so you can’t rely on it”? It is thought that the cause of the fluctuation of the numerical value is largely influenced by the measurement method and the amount of water in the body. I will explain the relationship between the impedance method for estimating body fat percentage and water, and the points to keep in mind in order to grasp the accurate value.
Can’t you count on your body fat percentage? What is the Bioimpedance method?
If you are measuring your daily weight with a scale or activity meter for health management, you may be worried about fluctuations in your body fat percentage. Even though your weight doesn’t change much, if your body fat percentage changes each time you measure it, you won’t know which value is correct. Fluctuations in body fat percentage are more likely to occur due to the method of measuring body composition.
Many manufacturers of weight scales and activity meters use a technique called the “bioimpedance method” as a method for measuring body composition. This is a method of estimating the body fat percentage by passing a weak current through the body and measuring the electrical resistance (= impedance) of how much current flows through the body.
Muscles contain more water than fat, and there are electrolytes that carry current. On the other hand, fat has the property of not conducting much current compared to muscle. Using this characteristic, the body fat percentage is estimated from the measured electrical resistance value and height / weight.
With this measurement method, the value of electrical resistance fluctuates depending on the water content in the body, so the amount of water in the body at that time also affects the body fat percentage.
Does body fat percentage decrease as the amount of water increases? Fluctuating body fat percentage
Body fat percentage varies depending on the amount of water in the body, but about 60% of the body weight of adult men and about 55% of the body weight of adult women is water. Moisture in the body can be roughly divided into three types: intracellular fluid, extracellular fluid , and blood. It is the extracellular fluid and blood that circulate in the body that are said to affect the measurement of body fat percentage.
Since we are affected by gravity, the water balance of the whole body becomes even when we lie down, such as when we are sleeping, but when we stand up, the water moves to the lower limbs over time. increase. In addition, the water in the body tends to accumulate in the legs in the evening when the desk work or standing work that keeps sitting down and the passage of time. In this way, the value tends to be unstable when measuring in a state where the water distribution in the body is biased.
In addition, exercise that promotes blood circulation also greatly affects the measured values. When you use your muscles to move your body, you have more blood flow to carry oxygen and nutrients to your muscles, resulting in more blood volume. At rest, about 5 liters of blood is pumped from the heart, but when exercising, it is said that 25 liters of blood per minute, which is about five times as much, is supplied to the whole body. It is thought that the increase in blood volume temporarily increases the amount of water in the body, which makes it easier for electric current to flow and lowers the value of body fat percentage.
Tips on how to measure body fat percentage
When estimating body fat percentage from body fat percentage, try to avoid times when blood flow is higher than usual, such as during exercise, after eating, and after bathing. Even immediately after waking up, the water distribution throughout the body is unstable due to the influence of gravity, so it will be easier to obtain more accurate values if you measure after a while after waking up.
Although water has a great effect on the measurement of body fat percentage, it is unlikely that the body fat percentage will decrease after drinking a glass of water because it is largely due to the water circulating in the body, and it is considered to be within the range of error. Is reasonable. On the other hand, if the body is dehydrated, the value of body fat percentage tends to be high, so it is possible that the body fat percentage is estimated to be low by hydration.
It is easy to feel uneasy when you see the change in body fat percentage, but it is just a reference value as a “point” that shows the state of the body at that time, and the “point” becomes a “line” for continuing measurement. You can grasp the tendency from the line. When exercise increases muscle mass, body fat percentage changes, and it also helps prevent swelling of water in the lower limbs. Keep in mind to move your body on a regular basis, and try to understand your body fat percentage and body fat mass as one of your health management.
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