The causes of obesity and the mysteries of fat cells

Part 1: Causes of Obesity

1. Fat and thin

"I've started gaining weight recently, what should I do?"

"You're so slim, I really admire you."

We often hear conversations like this in daily life. So what do "fat" and "thin" mean? We can't say that being heavy means being fat, or that being light means being thin. A wrestler weighing over 100kg has well-developed muscles and a strong physique, but that doesn't mean he's obese; conversely, an elderly woman weighing less than 50kg but with a bulky figure is not necessarily not obese.

What are the general standards for judging body fat by visual inspection? The standard is the percentage of body fat in one's weight. There are slight differences in body fat percentage between men and women, but it's generally around 20%. Body fat percentage = fat weight / body weight. Generally, boys and girls in puberty (around age 12) have about 20% body fat. By age 18, males' body fat percentage drops to 15%, while females' increases to over 20%. After age 18, both men and women show an upward trend. Normal body fat percentage is 15%–20% for men and 20%–25% for women. If it increases from 20% to 25%–30%, then one is considered overweight; conversely, if it decreases to 10%–15%, one is considered underweight. Therefore, weighing 100kg doesn't necessarily mean being obese, and weighing 50kg doesn't necessarily mean not being obese. In short, to gain weight, increase fat; to lose weight, reduce fat. This sounds simple, but it's very difficult to do. Especially when losing weight, simply reducing fat is extremely difficult.

It's possible to lose 3-5 kg ​​in a week by not eating anything. However, this actually reduces not only fat but also protein. This isn't true weight loss; it's more akin to developing diabetes. While you may lose weight, your overall body becomes weaker. Weight loss that only reduces fat makes you feel lighter and easier to climb stairs. Conversely, weight loss that reduces both fat and protein simultaneously weakens your constitution, leaving you breathless when climbing stairs.

So how can we lose weight healthily? To lose weight healthily, we must understand how body fat increases and decreases.

2. Fat for storing energy

Plant leaves contain chlorophyll, which can use solar energy, carbon dioxide, and water to produce starch. When a person eats starch, it is broken down in the body to produce glucose, which is then absorbed by the intestines and enters the bloodstream. The human body primarily relies on glucose, which contains solar energy, for its functions.

If too much glucose is stored in the body, some will be converted into glycogen, while most will be stored as fat. Compared to the remaining glucose stored as glycogen, fat only needs half the volume to store the same amount of energy. Therefore, fat is an excellent energy storage substance.

The glycogen stored in our bodies is the main energy source during sprinting, but the energy consumed when running a 42km marathon is mainly fat.

A fat molecule is composed of one glycerol molecule and three fatty acid molecules. Glycerol, also known as propanetriol, is a component of fats, phospholipids, and glycolipids. Fatty acids are hydrocarbon chains containing a carboxyl group and are also components of various lipids. Fatty acids contain a considerable amount of energy.

3. Locations where fat is stored

If you stir the oil used for frying fish, which is suspended in water, the small oil droplets will immediately turn into larger droplets and float on the surface. If this phenomenon were to occur in the human body, it would be very dangerous; blood vessels would quickly become blocked, causing hemiplegia. For example, a fracture caused by a traffic accident can also lead to hemiplegia. This is because fat from the center of the fractured bone enters the blood vessels, causing a blockage in the cerebral blood vessels. This is known as fat embolism.

But even if you frequently eat fatty foods, such as steak, you won't suffer from hemiplegia. Why is that? It turns out that before fat is absorbed into the bloodstream, the oil droplets are surrounded by proteins and phospholipids, forming lipoproteins. Lipoproteins, no matter how much they come into contact with each other, do not fuse and grow larger. The fat in blood vessels exists in the form of lipoproteins, and therefore does not fuse with each other.

Fat can be absorbed from food and also produced in the liver. Under normal circumstances, fat does not accumulate excessively in the liver, which has functions such as synthesizing albumin, converting ammonia into urea, and detoxification. However, if fat accumulates in the liver, it can cause problems and prevent the liver from performing its proper functions. Therefore, under normal circumstances, excess fat enters the bloodstream and exists in the form of lipoproteins.

So, if fat isn't stored in the intestines or liver, can it be stored in blood vessels? In blood vessels, fat can exist in the relatively safe form of lipoproteins, but it cannot be stored in a fixed form. Excessive accumulation in blood vessels can cause arteriosclerosis, so it must be eliminated. Therefore, there must be a place in the human body to store fat-this is adipose tissue. Fat is stored in fat cells. Besides fat cells, adipose tissue also contains collagen fibers, pre-adipocyte cells, vascular cells, and autonomic nerves. Adipose tissue is mainly distributed in the subcutaneous tissue of the abdomen and thighs, and around internal organs.