Causes of Obesity and Detailed Explanation of Simple and Secondary Obesity

What are the causes of obesity?

Obesity is caused by excessive fat storage in the body. The substances that sustain human life and bodily functions are mainly proteins, carbohydrates, lipids, minerals, and vitamins. If excessive fat intake exceeds physiological needs, some will be stored in the body. Similarly, excessive carbohydrate intake will also be converted into fat and stored. A normal adult's body fat should account for 10% to 20% of their body weight; exceeding this range leads to obesity.

The following are some of the main reasons why excessive fat accumulates in the body and causes obesity:

(1) The influence of genetic factors. Some statistics show that if both parents are obese, the incidence of obesity in their children is as high as 80% or more, and if one parent is obese, the incidence of obesity in their children can reach 40%.

(2) Excessive nutrition and insufficient consumption. For example, excessive food intake, excessive consumption of high-fat and high-calorie sugars, excessive sleep, lack of activity, and lack of physical exercise. This leads to an imbalance between calorie intake and consumption, with "supply" exceeding "expenditure," and excessive fat and sugar are converted into fat and stored in the body.

(3) Caused by certain diseases. The absorption and metabolism of carbohydrates, fats, and proteins in the body are regulated by the nervous and endocrine systems. If the nervous and endocrine systems are diseased, it will lead to disorders or dysfunctions in the metabolism of carbohydrates, fats, and proteins. Sequelae of meningitis, hypofunction of the pituitary gland, thyroid gland, and gonads, as well as tumors in the pituitary gland, adrenal glands, etc., can all cause disorders in the metabolism of carbohydrates, fats, and proteins, leading to obesity.

(4) Certain medications can cause obesity as a side effect while treating certain diseases. For example, treatment of asthma, rheumatism, rheumatoid arthritis, and allergic diseases with corticosteroids can lead to obesity, with fat mainly accumulating in the chest, back, and face (clinically known as "buffalo hump" or "moon face"). Phenothiazine drugs used to treat mental illness can also cause sexual dysfunction and obesity in patients.

The weight loss we usually refer to is obesity caused by the first two reasons, also known as "simple obesity." The third type is called secondary obesity. Treatment should target the underlying cause.

What is simple obesity?

Obesity is generally divided into two main categories: simple obesity and secondary obesity.

Secondary obesity is caused by an underlying medical condition. It can be diagnosed based on clinical presentation and test results. This type of obesity requires treatment from a doctor to address the underlying cause.

Obesity without a clear cause is called simple obesity, and the kind of obesity that we usually refer to as needing to lose weight is this kind of simple obesity.

Simple obesity can be further divided into constitutional obesity (also known as primary obesity) and acquired obesity. The former may have a family history of obesity or be obese since childhood, with fat cell proliferation and hypertrophy. The latter is mostly caused by excessive food intake and insufficient energy expenditure, resulting in cell hypertrophy, but without proliferation.

The causes of simple obesity are not fully understood. It is generally believed to be related to genetic factors, overeating, lack of physical activity, and psychological factors.

What is secondary obesity?

Obesity caused by a certain disease is called secondary obesity, also known as pathological obesity. Treating this type of obesity with the same methods as for simple obesity will not only be ineffective but may also delay proper treatment. Common types of secondary obesity include:

(1) Cortisol-induced obesity. This type of obesity is characterized by a swollen face, neck, and trunk, while the limbs are not swollen, and may even be slender. The face becomes round like a plate, hence the name "moon face," the shoulders and back become like a "buffalo hump," and the abdomen becomes swollen like a pregnant woman; medically, this is called "central obesity." In addition to obesity, there are also symptoms such as purple striae on the skin, hirsutism, high blood pressure, and sexual dysfunction. This disease is caused by hyperfunction of the adrenal cortex due to adrenal cortical hyperplasia, adenoma, or adenocarcinoma, resulting in excessive secretion of cortisol. Cushing first described this disease in 1932, so it is also called "Cushing's syndrome."

(2) Pituitary obesity. The obesity is similar to that of Cushing's syndrome and is caused by pituitary basophilic cell tumors. These tumors cause hyperfunction of the adrenal cortex and excessive secretion of cortisol.

(3) Brain obesity. This type of obesity is characterized by underdeveloped reproductive organs in adolescence and loss of sexual function, lack of sperm, decreased libido, amenorrhea, and infertility in adulthood. The breasts, lower abdomen, and area around the external genitalia are particularly obese, while the face and limbs are not obese. This type of obesity is caused by damage to the hypothalamus-pituitary region due to infection, tumors, or trauma, resulting in abnormal appetite, fat metabolism, and sexual function.

(4) Gonadal obesity. This type of obesity is caused by conditions such as removal of the ovaries during puberty in women, absence of testes in men, congenital testicular hypoplasia, or orchiectomy. This type of obesity is mainly located in the lower body, around the pelvis, thighs, and breasts.

(5) Obesity caused by hyperplasia of the inner table of the skull. This type of obesity is relatively rare and almost always occurs after menopause in women. The obesity is most pronounced in the trunk and proximal extremities. In addition, there are symptoms such as headache, hirsutism, and mental disorders. A skull X-ray showing hyperplasia of the frontal bone and other inner table bones can confirm the diagnosis. This may be related to autonomic nervous system dysfunction and pituitary insufficiency.

What is physiological obesity?

Physiological obesity refers to a state of excessive fat accumulation under normal physiological conditions due to the body's own needs. This type of obesity is beneficial to the body, such as childhood obesity, obesity during pregnancy and lactation, etc. In addition, certain special occupations also require a relatively large amount of fat accumulation, such as sumo wrestlers and weightlifters. Some people with physiological obesity may experience symptoms such as chest tightness, sweating, and shortness of breath, but they still fall into the category of simple obesity.

What is pathological obesity?

Pathological obesity encompasses a wide range, but mainly refers to obesity caused by a certain disease, such as Cushing's syndrome, hypothyroidism-related obesity, and post-hepatitis obesity. The presence of severe complications in simple obesity also indicates that the obesity has become pathological obesity.

In reality, the above classification is only a theoretical distinction and is difficult to measure clinically. Generally, the distinction is based solely on whether pathological changes occur. However, both pathological and irrational obesity can transform into each other. Further aggravation of physiological obesity can lead to pathological changes, becoming pathological obesity; conversely, with proper treatment, pathological obesity can gradually improve and transform back into physiological obesity, eventually restoring a normal physique.