Exploring the Roots of Obesity: From Genetics to the Mysterious Fat Cells

The causes and mechanisms of obesity are very complex, involving both genetic and environmental factors, and the body's energy balance and body fat homeostasis network are also crucial.

Genetic factors

The genetic factors of human obesity are quite complex. More than 20 obesity genes have been discovered, located on multiple different chromosomes, and play a very important role in determining the genetic phenotype of obesity.

Body mass index, skinfold thickness, local fat distribution, calorie intake metabolic rate, and calorie expenditure are all influenced by genetic factors.

Human energy balance and body fat homeostasis network

Obesity requires a period of positive energy balance, meaning that energy intake exceeds energy expenditure, and excess energy is stored in the body in the form of diglycerides.

What is the human energy balance and body fat homeostasis network?

It is generally believed that a decrease in the levels of glucose, amino acids, etc. in an individual's tissues will cause a feeling of hunger and promote the individual's eating.

After eating, pancreatic islet cells secrete insulin, which promotes increased triglyceride synthesis in adipocytes.

Increased triglyceride accumulation and enlarged fat cells promote leptin gene expression, leading to increased leptin synthesis and secretion.

Leptin acts as a signal of increased body fat to the leptin receptor in the hypothalamus, reducing food intake. At this time, triglycerides are broken down into glycerol and free fatty acids and released into the circulation, thus reducing the volume of fat.

When triglyceride accumulation decreases, the amount of leptin secreted into the circulation also decreases accordingly. The signal transmitted by the hypothalamic leptin receptor decreases, and the signal transmitted through the parasympathetic nervous system promotes eating, which in turn increases triglyceride synthesis.

This cycle repeats itself, forming a network that maintains the body's energy balance and body fat stability.

If any link in this network malfunctions, it can affect appetite and energy consumption, leading to the continuous accumulation of body fat and obesity.

Human fat cells are composed of cell membranes, nuclei, mitochondria, lipid droplets, and enzymes, among which lipid droplets make up a considerable proportion, so their size almost controls the size of the entire fat cell.

The enzymes that synthesize and break down fats directly regulate the metabolism of lipid droplets. Usually, the rates of synthesis and breakdown are consistent, thus maintaining the metabolic balance of lipids in the human body.

When the body has excess nutrition or lacks certain nutrients, or when there are genetic defects or lipid metabolism disorders, the rate of fat synthesis exceeds the rate of fat breakdown. The enlargement of lipid droplets causes fat cells to gradually increase in size, leading to obesity.

Studies have found that during the 30th week of fetal development and within one year after birth, human fat cells undergo a period of extremely active proliferation. During this period, excessive nutrition can increase the number of fat cells. Although the number of fat cells does not increase afterward, they can enlarge and increase weight. When losing weight, the number of fat cells remains unchanged but can shrink. This is one of the important reasons why overweight infants are more likely to become obese when they grow up.

Nutritional deficiencies can also lead to obesity.

If a person has a long-term unbalanced diet, eats overly refined foods, abuses oral nutritional supplements, or engages in improper dieting for weight loss, it can lead to insufficient intake of certain nutrients, thereby causing nutritional deficiency obesity.

Science has confirmed that a deficiency of certain nutrients in the human body can also lead to weight gain. The body needs the participation of various nutrients to complete the process of energy metabolism and fat conversion into energy release and consumption, such as B vitamins, niacin, iron, calcium, zinc, etc. These nutrients are abundant in vegetables, fruits and whole grains. If the intake is insufficient, it will affect the conversion and metabolism of energy, resulting in excess energy in the body, excessive fat storage and insufficient consumption, thus causing weight gain.

Diseases can also lead to obesity

There are two main causes of obesity: one is that the body's intake exceeds its expenditure, and the other is that it is caused by disease.

For the latter type of obesity, relying solely on weight loss to achieve a therapeutic goal is actually harmful to health.

Cushing's syndrome

Also known as hyperadrenocortical syndrome, it can cause central obesity, resulting in significant fat accumulation on the neck and back, thinning of the skin, and susceptibility to purple striae and petechiae.

Female patients may experience symptoms such as decreased menstrual flow or even amenorrhea.

hypothyroidism

It is a systemic disease caused by insufficient synthesis or physiological effects of thyroid hormones, and obesity is partly caused by reduced calorie consumption.

The patient has pale skin, a swollen face, and has lost the outer third of his eyebrows.

Hypothalamic obesity

The hypothalamus is the command center for endocrine, metabolic, body temperature, and sexual functions, and the feeding center is also located within it.

Hypothalamic obesity is often caused by trauma, inflammation, hemorrhage, tumors, etc., which stimulate the hypothalamus, making patients prone to hunger and eating large amounts of food, leading to rapid weight gain.

Gonadal obesity

Obesity caused by conditions such as removal of the ovaries during puberty in women, anorchia in men, congenital testicular hypoplasia, or orchiectomy.

This type of obesity mainly occurs in the lower body, around the pelvis, thighs, and breasts.

Polycystic ovary syndrome

It is more common in women aged 20-40 and is related to dominant inheritance of chromosomes.

It is often accompanied by menstrual disorders, hirsutism, amenorrhea, infertility, etc., and some individuals may exhibit masculinization.

Dysmenorrhea-related obesity

It is a type of lipemia, and patients are mostly postmenopausal women.

Aside from early menopause and early decline in sexual function, the patient had no other specific symptoms.

Inner table hyperplasia

This type of obesity almost always occurs in postmenopausal women, with the most noticeable fat deposits in the trunk and proximal limbs.

In addition, it is often accompanied by symptoms such as headache, hirsutism, and mental disorders.