The body's chemical composition: the secrets of water, blood, muscles, and the brain

**The body's chemical composition**

Understanding the body's chemical composition is crucial for controlling obesity, as it reveals the percentage of body weight each component makes up. Water makes up 65% of the body's weight. A 70kg adult, after dehydration, weighs only 25kg, comprising 3kg of carbohydrates, 7kg of fat, 12kg of protein, and 3kg of minerals. Blood accounts for approximately 8% of total body weight. Losing more than 20% of blood volume at once hinders vital functions. Healthy individuals generally recover quickly from blood loss of less than 10%. The human body contains 639 muscles, composed of approximately 6 billion muscle fibers, ranging in length from 60cm to about 1mm. Large muscles weigh 2000g, while smaller ones weigh only a few grams. Muscles typically account for 35% to 40% of body weight. The total length of capillaries within muscles can reach 100,000 kilometers, enough to circle the Earth two and a half times. The brain is composed of approximately 14 billion cells, weighs about 1400 grams, has a cerebral cortex that is 2-3 millimeters thick, and a total surface area of ​​about 2200 square centimeters. 100,000 to 100,000 brain cells die every day; the less we use our brains, the more brain cells die. The information storage capacity of a single person's brain is equivalent to 10,000 libraries, each with 20 million books. Even the most mentally adept person only uses about 10% of their brain's capacity in their lifetime. The main component of the human brain is water, accounting for 80%. Although it only accounts for 2% of body weight, it consumes 25% of the body's oxygen and accounts for 15% of the blood flow from the heart, with 2000 liters of blood flowing through the brain daily. The energy consumed by the brain, expressed in electrical power, is approximately equivalent to 25 watts.

What are the functions of fat in our bodies?

During a hospital physical examination, the first thing we usually measure is our weight. This weight includes the total weight of bones, muscles, organs, body fluids, and adipose tissue. Therefore, using a scale alone cannot tell us whether weight loss is due to water, muscle, or fat. Human body weight is composed of bones, muscles, water, and fat. It's clear that the composition and changes in weight are complex, and using only the Body Mass Index (BMI) to measure a person's weight is incomplete. Next, we will discuss the factors related to obesity, including bones, fat, muscle, and water.

The amount of fat is the true standard for determining whether a person is obese. Fat is the least dense component of the human body, characterized by its low density and large volume. The body fat percentage we mentioned earlier is closely related to fat. So, let's start with fat. Fat is a substance we often mention, are familiar with, yet don't fully understand. In modern society, in some people's eyes, fat's "social image" has become negative. Hearing the word "fat" immediately conjures up images of an obese figure, unhealthy diet, and the culprit behind certain chronic diseases. Is fat really that bad? What is its connection to obesity? Excessive fat intake leads to obesity, making us immobile, and produces excessively high blood lipids, inducing chronic diseases such as hypertension and heart disease. Increased total dietary fat intake also increases the probability of certain cancers. Someone once asked if it's good to only eat vegetables and not meat. In fact, consuming meat in moderation is beneficial to health. However, meat contains a large amount of saturated fat, which is closely related to the formation of harmful cholesterol. Accumulated cholesterol can clog arteries, and excessive consumption can easily lead to stroke and heart disease, cause inflammation, and may even trigger arthritis and asthma, shortening lifespan. As long as we control the amount, alternating between fish, meat, and poultry, and not exceeding the recommended daily intake as suggested in the Chinese Dietary Guidelines, it's fine.