Obesity is a chronic, progressive metabolic disease characterized by excessive accumulation of body fat, particularly triglycerides, resulting from excess energy intake or altered body metabolism. This condition leads to excessive weight gain and a cascade of pathophysiological changes in the body. It is also referred to as obesity and metabolic diseases or simply obesity. Over the past few decades, the prevalence of obesity has steadily risen worldwide, largely due to changes in dietary habits and lifestyle.
Etiology
The development of obesity is a complex process involving the interplay of multiple factors, including genetic and environmental influences.
Genetic Factors
Genetic influences, such as gene mutations, play a significant role in determining an individual's susceptibility to obesity. Gene mutations can affect physiological processes such as appetite, metabolic rate, and fat storage, thereby increasing the risk of obesity.
Environmental Factors
Environmental contributors include food types and structures, eating behaviors, psychological stress, and substance misuse. These factors can lead to increased food intake or reduced calorie expenditure, with excess energy being converted into fat, resulting in weight gain. For example, psychological stress can drive some individuals to overeat as a coping mechanism, while substance misuse may alter appetite or metabolism, further exacerbating the obesity problem.
Risks
Obesity affects not only physical appearance, causing inconvenience in daily life, but also poses risks for a wide array of metabolic diseases. These include insulin resistance, type 2 diabetes mellitus (T2DM), hypertension, dyslipidemia, hyperuricemia, gout, and nonalcoholic fatty liver disease. As such, the term "obesity and metabolic diseases" is often employed.
In addition to these metabolic disorders, obesity is associated with a variety of non-metabolic obesity-related conditions, such as obstructive sleep apnea syndrome, osteoarthritis, polycystic ovary syndrome, acanthosis nigricans, venous thrombosis, heart failure, respiratory failure, and numerous malignancies (e.g., breast, endometrial, prostate, gastric, colorectal, and thyroid cancers). Obesity affects nearly every organ system, and the risk of obesity-related diseases increases in proportion to the severity of obesity. Severe obesity reduces life expectancy, particularly in young males. Furthermore, obesity may negatively affect mental health, contributing to conditions such as depression, anxiety disorders, and bipolar disorder.
Diagnosis
The diagnosis of obesity is commonly based on body mass index (BMI), although body fat percentage, waist circumference, waist-to-hip ratio (WHR), and visceral fat content are also useful diagnostic parameters.
Body Mass Index (BMI)
Diagnostic BMI thresholds vary by region due to ethnic differences. According to the World Health Organization (WHO), obesity is defined as a BMI ≥ 30 kg/m2.
Body Fat Percentage
Body fat percentage reflects the proportion of fat relative to total body weight. In healthy adults, a normal range is 10–20% for males and 15–25% for females. Obesity is diagnosed when body fat exceeds 25% in males and 30% in females.
Waist Circumference
Waist circumference provides an estimate of abdominal visceral fat. Obesity is diagnosed when waist circumference is ≥85 cm in males and ≥80 cm in females. In many Asian populations, central (abdominal) obesity is more prevalent.
The diagnosis of obesity often relies on a combination of these three indicators: BMI, body fat percentage, and waist circumference.
Staging and Grading
Staging
There are 3 stages:
- Compensatory Stage: Obesity without metabolic or obesity-associated diseases, accounting for approximately 30% of cases.
- Decompensatory Stage (Morbid Obesity): Obesity accompanied by one or more metabolic or obesity-associated diseases, accounting for approximately 70% of cases.
- End-Stage Organ Failure: Obesity with severe complications such as cardiac or pulmonary failure.
Grading by BMI
There are 4 grades:
- Mild Obesity (Grade I): BMI of 28–32.49 kg/m2.
- Moderate Obesity (Grade II): BMI of 32.50–37.49 kg/m2.
- Severe Obesity (Grade III): BMI of 37.50–49.99 kg/m2.
- Extreme Obesity (Grade IV): BMI ≥ 50 kg/m2.
Treatment
Treatment options include dietary control combined with exercise therapy, pharmacotherapy, and bariatric surgery. Similar to other chronic conditions, a multimodal approach is generally necessary. Although non-surgical approaches offer some benefits, long-term outcomes are often less satisfactory, even with significant recent advancements in anti-obesity medications. As a result, bariatric surgery, which produces rapid and significant therapeutic effects, has garnered increasing attention.
Research has demonstrated that bariatric surgery not only leads to substantial weight reduction but also reverses or alleviates metabolic diseases such as T2DM and other obesity-related conditions. This has given rise to the emerging field of obesity metabolic surgery, also known as bariatric surgery or metabolic-bariatric surgery.
To be continued