Obesity
Obesity is a medical condition, considered by multiple organizations to be a disease, in which excess body fat has accumulated to such an extent that it can have negative effects on health. People are classified as obese when their body mass index —a person's weight divided by the square of the person's height—is over ; the range is defined as overweight. Some East Asian countries use lower values to calculate obesity. Obesity is a major cause of disability and is correlated with various diseases and conditions, particularly cardiovascular diseases, type 2 diabetes, obstructive sleep apnea, certain types of cancer, and osteoarthritis.
Obesity has individual, socioeconomic, and environmental causes. Some known causes are diet, low physical activity, automation, urbanization, genetic susceptibility, medications, mental disorders, economic policies, endocrine disorders, and exposure to endocrine-disrupting chemicals.
While many people with obesity attempt to lose weight and are often successful, maintaining weight loss long-term is rare. Obesity prevention requires a complex approach, including interventions at medical, societal, community, family, and individual levels. Changes to diet as well as exercising are the main treatments recommended by health professionals. Diet quality can be improved by reducing the consumption of energy-dense foods, such as those high in fat or sugars, and by increasing the intake of dietary fiber. The World Health Organization stresses that the disease is a societal responsibility and that these dietary choices should be made the most available, affordable, and accessible options. Medications can be used, along with a suitable diet, to reduce appetite or decrease fat absorption. If diet, exercise, and medication are not effective, a gastric balloon or surgery may be performed to reduce stomach volume or length of the intestines, leading to feeling full earlier, or a reduced ability to absorb nutrients from food. Metabolic surgery promotes weight loss not only by reducing caloric intake but also by inducing sustained changes in the secretion of gut hormones involved in appetite and metabolic regulation.
Obesity is a leading preventable cause of death worldwide, with increasing rates in adults and children. In 2022, over 1 billion people lived with obesity worldwide, representing more than a double of adult cases registered in 1990. Obesity is more common in women than in men. Obesity is stigmatized in most of the world. Conversely, some cultures, past and present, have a favorable view of obesity, seeing it as a symbol of wealth and fertility. The World Health Organization, the US, Canada, Japan, Portugal, Germany, the European Parliament and medical societies classify obesity as a disease. Others, such as the UK, do not.
Classification
| Category | BMI |
| Underweight | < 18.5 |
| Ideal weight | |
| Overweight | 25.0 – 29.9 |
| Obese | 30.0 – 34.9 |
| Obese | 35.0 – 39.9 |
| Obese | ≥ 40.0 |
File:Obesity6.JPG|thumb|upright=1.2|alt=A front and side view of a "class III obese male" torso. Stretch marks of the skin are visible along with gynecomastia.|A "class III obese male" with a BMI of 53 kg/m2: weight, height. He presents with stretch marks and enlarged breasts.
Obesity is typically defined as a substantial accumulation of body fat that could impact health. Medical organizations tend to classify people living with obesity as based on body mass index – a ratio of a person's weight in kilograms to the square of their height in meters. For adults, the World Health Organization defines "overweight" as a BMI 25 or higher, and "obesity" as a BMI 30 or higher. The U.S. Centers for Disease Control and Prevention further subdivides obesity based on BMI, with a BMI 30 to 35 called class 1 obesity; 35 to 40, class 2 obesity; and 40+, class 3 obesity.
For children, obesity measures take age into consideration along with height and weight. For children aged 5–19, the WHO defines obesity as a BMI two standard deviations above the median for their age. For children under five, the WHO defines obesity as a weight three standard deviations above the median for their height.
Some modifications to the WHO definitions have been made by particular organizations. The surgical literature breaks down class II and III or only class III obesity into further categories whose exact values are still disputed.
- Any BMI ≥ 35 or 40 kg/m2 is severe obesity.
- A BMI of ≥ 35 kg/m2 and experiencing obesity-related health conditions or ≥ 40 or 45 kg/m2 is morbid obesity.
- A BMI of ≥ 45 or 50 kg/m2 is super obesity.
The preferred obesity metric in scholarly circles is the body fat percentage – the ratio of the total weight of person's fat to his or her body weight, and BMI is viewed merely as a way to approximate BF%. According to American Society of Bariatric Physicians, levels in excess of 32% for women and 25% for men are generally considered to indicate obesity.
BMI is now viewed as outdated in some countries because it ignores variations between individuals in amounts of lean body mass, particularly muscle mass. Individuals involved in heavy physical labor or sports may have high BMI values despite having little fat. For example, more than half of all NFL players are classified as "obese", and 1 in 4 are classified as "extremely obese", according to the BMI metric. However, their mean body fat percentage, 14%, is well within what is considered a healthy range. Similarly, Sumo wrestlers are typically categorized by BMI as "severely obese" or "very severely obese"; but one study of college-aged Sumo wrestlers found that 40% of them were no longer categorized as obese when body fat percentage was used instead of BMI; this was attributed to their very high lean body mass.
Canada utilises BMI sparingly within their method of defining levels of obesity through use of the Edmonton Scale. This scale also introduces factors such as Quality of Life, Mental Health & Mobility amongst others. In recent years, Canada chose to allow both Chile & Ireland to adapt their obesity guidelines to suit both countries' health systems. In Ireland, obesity is now defined as "a Complex, Chronic & Relapsing Disease".
Effects on health
Obesity increases a person's risk of developing various metabolic diseases, cardiovascular disease, osteoarthritis, Alzheimer disease, depression, and certain types of cancer. Depending on the degree of obesity and the presence of comorbid disorders, obesity is associated with an estimated 2–20 year shorter life expectancy. High BMI is a marker of risk for, but not a direct cause of, diseases caused by diet and physical activity.Mortality
Obesity is one of the leading preventable causes of death worldwide. The mortality risk is lowest at a BMI of 20–25 kg/m2 in non-smokers and at 24–27 kg/m2 in current smokers, with risk increasing along with changes in either direction. This appears to apply in at least four continents. Other research suggests that the association of BMI and waist circumference with mortality is U- or J-shaped, while the association between waist-to-hip ratio and waist-to-height ratio with mortality is more positive. In Asians the risk of negative health effects begins to increase between 22 and 25 kg/m2. In 2021, the World Health Organization estimated that obesity caused at least 2.8 million deaths annually. On average, obesity reduces life expectancy by six to seven years, a BMI of 30–35 kg/m2 reduces life expectancy by two to four years, while severe obesity reduces life expectancy by ten years.Morbidity
Obesity increases the risk of many physical and mental conditions. These comorbidities are most commonly shown in metabolic syndrome, a combination of medical disorders which includes: diabetes mellitus type 2, high blood pressure, high blood cholesterol, and high triglyceride levels. A study from the RAK Hospital found that obese people are at a greater risk of developing long COVID. The CDC has found that obesity is the single strongest risk factor for severe COVID-19 illness.Complications may be either directly caused by obesity or indirectly related through mechanisms sharing a common cause such as a poor diet or a sedentary lifestyle. The strength of the link between obesity and specific conditions varies. One of the strongest is the link with type 2 diabetes. Excess body fat underlies 64% of cases of diabetes in men and 77% of cases in women.
Health consequences fall into two broad categories: those attributable to the effects of increased fat mass and those due to the increased number of fat cells. Increases in body fat alter the body's response to insulin, potentially leading to insulin resistance. Increased fat also creates a proinflammatory state, and a prothrombotic state.