Obesity is a common and ancient metabolic syndrome. When the calories consumed by the human body exceed the calories expended, the excess calories are stored as fat in the body. When this amount surpasses normal physiological requirements and reaches a certain threshold, it develops into obesity.

bubble_chart Etiology

The pathogenesis of obesity can be attributed to the following two groups of factors:

1. Intrinsic factors: Internal factors within the human body that disrupt fat metabolism, leading to obesity.
   1. Genetic factors: The development of simple obesity in humans also has a certain genetic background. Human obesity is generally considered to be polygenic, with genetics playing a predisposing role in its onset. The formation of obesity is also related to the interaction of lifestyle behaviors
   2. , such as eating habits, preferences, insulin response, and psychosocial factors.
   3. Neuropsychiatric factors: There are two pairs of nuclei in the human hypothalamus related to eating behavior. One pair is the ventromedial nucleus, also known as the satiety center, and the other is the lateral hypothalamic nucleus, also called the hunger center. When the satiety center is stimulated, it induces a feeling of fullness and suppresses appetite; when damaged, it leads to increased appetite. Conversely, stimulation of the hunger center increases appetite, while its damage results in anorexia and refusal to eat. Under physiological conditions, these centers maintain a dynamic balance, regulating appetite within a normal range and maintaining a healthy body weight. The blood-brain barrier in the hypothalamus is relatively weak, an anatomical feature that allows various bioactive factors in the blood to migrate there easily, influencing eating behavior. These factors include glucose, free fatty acids, norepinephrine, dopamine, serotonin, insulin, and others. Additionally, psychological factors often affect appetite, as the feeding center is influenced by mental state. When under excessive stress with sympathetic excitation or adrenergic stimulation (especially when α-receptors dominate), appetite is suppressed. Conversely, when the vagus nerve is stimulated and insulin secretion increases, appetite often becomes hyperactive.
   4. Hyperinsulinemia: In recent years, the role of hyperinsulinemia in the pathogenesis of obesity has drawn attention. Obesity often coexists with hyperinsulinemia, and while the causal relationship requires further investigation, it is generally believed that hyperinsulinemia contributes to obesity. Individuals with hyperinsulinemic obesity release approximately three times more insulin than normal individuals.
      Insulin has a significant role in promoting fat accumulation and can, to some extent, serve as a monitoring factor for obesity. Insulin promotes body fat increase through the following mechanisms: (1) facilitating glucose entry into cells, thereby synthesizing neutral fats; (2) inhibiting fat mobilization in adipocytes.
      The coexistence of excessive food intake and hyperinsulinemia is often a critical factor in the onset and maintenance of obesity.
   5. Abnormal brown adipose tissue: Brown adipose tissue is a type of fat tissue discovered only in recent years, distinct from white adipose tissue, which is primarily distributed subcutaneously and around internal organs. Brown adipose tissue has a limited distribution, found only in the interscapular region, neck, armpits, mediastinum, and around the kidneys. It appears light brown and exhibits relatively small changes in cell volume.
      White adipose tissue serves as an energy storage form, where the body stores excess energy as neutral fats. The volume of white adipocytes varies significantly with energy release and storage.
      Brown adipose tissue functions as a thermogenic organ. When the body consumes food or is exposed to cold, the fat in brown adipocytes burns, determining the body's energy metabolism level. These two scenarios are referred to as diet-induced thermogenesis and cold-induced thermogenesis, respectively.
      Brown adipose tissue directly participates in the overall regulation of body heat, dissipating excess heat to the external environment and maintaining energy balance.
      Research on brown adipose tissue in human obesity is limited, but some patients with thermogenic dysfunction-related obesity have indeed been observed.
   6. Other hormones are important factors in regulating fat metabolism, especially the synthesis and mobilization of triglycerides. The increase or decrease in these processes is determined by hormones through the regulation of enzymes. Among them, insulin and prostaglandin E1 are the main hormones that promote fat synthesis and inhibit breakdown, while catecholamines, glucagon, ACTH, MSH, TSH, GH, ADH, and glucocorticoids are hormones that promote fat breakdown and inhibit synthesis. If the former is secreted excessively and the latter is insufficient, it can lead to increased fat synthesis, exceeding breakdown and resulting in obesity. This group of endocrine factors is more closely related to secondary obesity.
2. External causes: mainly due to excessive eating and insufficient physical activity (as previously mentioned).

bubble_chart Clinical Manifestations

The clinical manifestations of obesity vary depending on the {|###|}disease cause{|###|}. Secondary {|###|}obesity{|###|} presents not only with obesity but also with the symptoms of the primary disease. Below, we focus on simple obesity. This condition can occur at any age: juvenile-onset cases exhibit obesity from childhood, while adult-onset cases typically begin between ages 20–25. However, clinically, it is most common among middle-aged women aged 40–50, and is also frequently seen in the elderly aged 60–70 and above. In men, fat distribution is primarily in the neck, trunk, and head, whereas in women, it tends to accumulate in the abdomen, lower abdomen, chest (breasts), and buttocks. Grade I {|###|}obesity{|###|} is often asymptomatic, whereas moderate to Grade III {|###|}obesity{|###|} may present with the following syndromes:

1. **Alveolar Hypoventilation Syndrome**: Also known as Pickwickian syndrome. Due to excessive fat accumulation in the body, increased weight, and the higher energy and oxygen consumption required for movement, individuals with {|###|}obesity{|###|} generally dislike physical activity, move little, and feel drowsy. Even mild exertion or physical labor can lead to fatigue. While total oxygen uptake increases in {|###|}obesity{|###|}, it is lower per unit of body surface area compared to normal. When fat deposits are prominent in the chest and abdomen, the abdominal wall thickens, the diaphragm elevates, and breathing becomes difficult, leading to CO₂ retention. PCO₂ often exceeds 6.3 kPa (48 mmHg) (normal: 5.3 kPa (40 mmHg)), resulting in hypoxia, shortness of breath, and even secondary polycythemia, pulmonary {|###|}stirred pulse{|###|} hypertension, and chronic {|###|}lung heart disease{|###|}, which can progress to heart failure. These conditions may improve with weight loss. Due to chronic hypoxia and CO₂ retention, patients often appear fatigued and drowsy, a condition termed Pickwickian syndrome.
2. **Cardiovascular Syndrome**: In Grade III {|###|}obesity{|###|}, the increase in blood vessels within adipose tissue raises effective circulating blood volume, cardiac output, and workload, sometimes accompanied by hypertension and {|###|}stirred pulse{|###|} atherosclerosis, further straining the heart. This can lead to left ventricular hypertrophy, compounded by fat deposition within and around the myocardium, increasing the risk of myocardial strain, left ventricular dilation, and left {|###|}heart failure{|###|}. Combined with the aforementioned alveolar hypoventilation syndrome, sudden death may rarely occur. Peripheral vascular resistance is typically normal or slightly reduced, and blood supply per unit weight is diminished. These symptoms may alleviate or resolve with weight loss.
3. Endocrine and metabolic disorders: Fasting and postprandial plasma insulin levels are elevated, with baseline values reaching 30 μU/ml and postprandial levels up to 300 μU/ml, approximately double those of normal individuals. Patients exhibit both hyperinsulinemia and increased C-peptide secretion, alongside insulin resistance (hypertrophic adipocytes are less sensitive to insulin, and insulin receptor numbers are reduced), leading to impaired glucose tolerance or diabetes. Total lipids, cholesterol, triglycerides, and free fatty acids are often elevated, resulting in hyperlipidemia and hyperlipoproteinemia, which form the basis for conditions such as atherosclerosis, coronary heart disease, and cholelithiasis. In obesity, plasma total protein, albumin, and globulin levels are typically within the normal range, though certain amino acids—such as arginine, leucine, isoleucine, tyrosine, and phenylalanine—may increase. This elevation in blood glucose and plasma amino acids creates a vicious cycle that stimulates pancreatic β-cells, thereby exacerbating obesity. Thyroid function is generally normal, with T3 increasing during overeating and decreasing during dietary restriction, while T4 remains unchanged. A small proportion of patients (reported in the literature as 2–18%) exhibit reduced ¹³¹I uptake, but TSH and T3 release in response to TRH are normal, indicating that the hypothalamic-pituitary-thyroid axis remains intact. In obesity, T3 receptor numbers decrease, likely contributing to reduced thermogenesis, though this can normalize after weight loss. Blood cortisol levels and 24-hour urinary 17-hydroxycorticosteroids and 17-ketosteroids may be slightly elevated, but dexamethasone suppression tests and circadian rhythms remain intact, suggesting normal adrenal cortical function with the aforementioned changes attributable to obesity. Growth hormone (GH) secretion is blunted in response to hypoglycemia and arginine stimulation. GH concentrations in obese individuals vary by age group: those under 25 have lower levels than normal, inversely correlating with body weight, while those over 30 exhibit levels comparable to normal individuals. Despite reduced GH secretion in obese adolescents, growth is unimpaired due to normal levels of growth mediators. Female obesity is often associated with amenorrhea and infertility, indicating gonadal dysfunction, and may present with polycystic ovaries accompanied by oligomenorrhea or amenorrhea, hirsutism, and virilization. Male obesity is marked by more pronounced changes in sex hormones, with increased estrogen and decreased androgen levels, frequently leading to erectile dysfunction, infertility, and eunuchoidism.
4. Digestive system syndrome: Excessive appetite, polyphagia, constipation, abdominal distension, and fullness are more common. Those with obesity may have varying degrees of hepatic steatosis and hepatomegaly, while those with cholelithiasis have a history of chronic dyspepsia and biliary colicky pain.
5. Others: Individuals with obesity may exhibit abnormal purine metabolism and increased plasma uric acid, significantly raising the incidence of pain wind compared to normal individuals, while those with coronary heart disease have a history of cardiac colicky pain. Patients may develop light purple or white striae on the skin, distributed over the lateral buttocks, inner thighs, knee joints, lower abdomen, etc. Folds are prone to abrasion, leading to dermatitis or tinea. They often sweat excessively, fear heat, and have lower resistance, making them susceptible to infections.

bubble_chart Diagnosis

Diagnosis can be made based on signs and body weight. First, the standard body weight must be determined according to the patient's age and height (refer to the standard body weight chart) or calculated using the following formula: Standard body weight (kg) = [Height (cm) - 100] × 0.9. If the patient's actual body weight exceeds the standard body weight by 20%, a diagnosis of obesity can be made, but factors such as muscle development or water retention must be excluded. Clinically, in addition to signs and body weight, the following diagnostic methods can be used:

1. Measurement of subcutaneous fat thickness using skinfold calipers: Since 1/2 to 2/3 of the body's total fat is stored subcutaneously, measuring subcutaneous fat thickness is representative and is simple and repeatable. Common measurement sites include the triceps skinfold thickness and the subscapular skinfold thickness. For adults, if the sum of these two measurements is ≥4 cm in males or ≥5 cm in females, a diagnosis of obesity can be made. Measurements from multiple sites improve reliability.
2. Estimation of subcutaneous fat thickness via X-ray.
3. Calculation based on the Body Mass Index (BMI) (weight/height² (kg)/(m²)). A BMI >24 indicates obesity.

1. If symptoms such as hypertension, central obesity, purple striae, amenorrhea, and elevated 24-hour urinary 17-hydroxycorticosteroids are present, Cushing's syndrome should be considered. A low-dose (2 mg) dexamethasone suppression test may be performed for differentiation.
2. Patients with a low metabolic rate should undergo further thyroid function tests (T3, T4, TSH) to rule out hypothyroidism.
3. For patients with anterior pituitary dysfunction or hypothalamic syndrome, pituitary and target gland endocrine tests, as well as examinations of the sella turcica, visual fields, and vision, should be conducted. If necessary, a cranial CT scan may be performed. Enlargement of the sella turcica suggests a pituitary tumor, but empty sella syndrome should also be excluded.
4. Amenorrhea, infertility, and virilization should prompt consideration of polycystic ovary syndrome.
5. In cases without obvious endocrine disorders but with afternoon foot swelling that improves in the morning, water and sodium retention-related obesity should be excluded. The orthostatic water test can be helpful.
6. Additionally, attention should be paid to accompanying conditions such as diabetes, coronary heart disease, atherosclerosis, gout, and gallstones.
7. For other rare types of obesity, diagnosis should be based on their specific clinical features.

bubble_chart Treatment Measures

Epidemiological studies from the 1990s indicate that the prevalence of simple obesity among adolescents in mainland China had reached an alarmingly uncontrolled level. During a physical examination at a school in Beijing, it was found that up to 27.8% of adolescents were overweight, with some exceeding the normal weight by 20%. The severe mental stress, psychological conflicts, and blows to self-confidence experienced by obese adolescents can have long-term effects on their personality, temperament, potential development, as well as future abilities and interpersonal relationships.

According to surveys, many adolescents currently resort to weight-loss methods commonly used by adults, such as taking diet pills, fasting, or undergoing physical therapies. However, growth and development are unique physiological processes during adolescence, and experts emphasize that adolescents should not engage in weight or fat loss.

Experts recommend that adolescent weight management should adhere to the following prohibitions: first, avoid starvation, semi-starvation, or disguised starvation therapies; second, avoid rapid short-term weight loss; third, avoid any weight-loss medications; and fourth, avoid surgical or physical treatments. These methods not only hinder physical growth but also impair the development of organs, tissues, muscles, and bones. Dramatic weight fluctuations in a short period can lead to imbalances in water-electrolyte and internal circulation, as well as metabolic disorders, causing significant harm to the cardiovascular, liver, and kidney systems.

Studies have shown that adolescent weight control should adopt a comprehensive approach, recognizing obesity as a chronic disease closely linked to unhealthy lifestyle behaviors. Both children and parents should avoid rushing the process. Key strategies include slowing down eating speed, avoiding "red-light" foods such as chocolate, sweets, candies, fatty meats, sugary drinks, and puffed snacks; limiting "yellow-light" foods like rice, pasta, potatoes, sweet potatoes, apples, and watermelon; and prioritizing "green-light" foods such as cabbage, bok choy, cucumber, wild celery, carrots, lean meat, eggs, milk, chicken, fish, mushrooms, oranges, and yogurt.

Simple obesity in adolescents is not only a serious health issue but also inflicts psychological harm. Parents should assist them in managing and reducing weight in a reasonable and effective manner to lead a healthy life.