[Kim Jaeho's Life Story]<179> The Devotion of Adipose Tissue

We obtain the energy necessary for living through daily meals, but even if we do not eat for more than a week and only drink water due to certain circumstances, it does not cause major problems or harm our health. When we resume eating, starting with very small amounts and gradually increasing to normal meals, the lost weight is easily regained, and health can even improve. For this reason, some people intentionally fast once a year.

The reason why not eating for a considerable period does not cause serious problems is that the body can use stored energy. Our body uses carbohydrates, proteins, and fats as energy sources. When new energy is not supplied, the liver and muscles break down stored glycogen and some muscle protein to use for about two to three days, then switch to using fat stored in adipose tissue.

Adipose tissue, commonly known as body fat, is mostly composed of fat cells within loose connective tissue that contains numerous nerves and blood vessels. It is distributed throughout the body, mainly under the skin (subcutaneous fat), around internal organs (visceral fat), between muscles, inside bone marrow, and within breast tissue. It stores energy in the form of fat and releases it when energy is not supplied, while also providing insulation and cushioning functions.

Nowadays, companies fiercely compete to reduce the size and weight of batteries while increasing their charge capacity, but adipose tissue performs energy storage much more efficiently. Carbohydrates and proteins produce 4 calories of energy per gram each, whereas fat produces 9 calories per gram, making it highly effective for storage. Carbohydrates serve as temporary storage, while most long-term storage is performed by fat for this reason.

The fat accumulated in adipose tissue comes from food or is primarily synthesized in the adipose tissue itself and also in the liver. When adipose tissue receives hormonal signals indicating the need for energy, it breaks down stored triglycerides into fatty acids and glycerol, which are then sent to the organs and tissues that require them.

How long can one endure on stored fat when unable to eat? According to research, typically more than 100,000 calories can be supplied, which is enough for an adult male consuming 2,500 calories per day to last about 40 days. Compared to batteries in mobile phones or electric cars, which are judged by how long they can be used on a single charge, this is a sufficient amount unlikely to be insufficient in daily life.

Unless in special situations like severe malnutrition, the fat stored in adipose tissue alone can supply energy for over a month, so there is no need to increase fat storage further. What about reality? In Korea, it is rare for people to have insufficient fat storage that harms health; rather, excessive fat storage leading to obesity is common, making it important to address problems caused by obesity.

From the perspective of energy storage alone, storing more fat does not cause major problems. The issue arises not from the energy storage function of adipose tissue but from its other functions. Recently, it has been revealed that adipose tissue plays a dedicated role as an endocrine organ synthesizing numerous biological compounds that regulate metabolic homeostasis, and obesity disrupts this function.

Hormones and cytokines (proteins secreted by immune cells) produced extensively by adipose tissue, such as leptin and adiponectin, are involved in glucose metabolism, lipid metabolism, inflammation, blood clotting, blood pressure, and feeding behavior. They affect the metabolism and function of many organs and tissues, including muscles, liver, blood vessels, and brain. Obesity disrupts the secretion of these hormones and cytokines, causing type 2 diabetes, hypertension, hyperlipidemia, myocardial infarction, stroke, and various vascular diseases.

To prevent and cure various diseases caused by obesity and ensure the dedicated functions of adipose tissue are not wasted, obesity must be improved. The key is to improve lifestyle habits by reducing energy intake and increasing energy expenditure. To reduce energy intake, dietary habits should be improved toward healthy eating (see Life Story episode 63), and to increase energy expenditure, physical activity should be actively promoted.

Kim Jaeho, Independent Researcher