Obesity is a complex medical condition defined by an excess accumulation of body fat to the extent that it can have a negative effect on health. It is a chronic and progressive disease influenced by a combination of genetic and environmental factors. Globally, it represents a significant public health challenge, with rates having more than doubled since 1990.
Methods for Assessing Obesity
The most widely used screening tool for assessing obesity is the Body Mass Index (BMI), a calculation that divides a person’s weight in kilograms by the square of their height in meters (kg/m²). According to the World Health Organization (WHO), a BMI between 25.0 and 29.9 indicates overweight, and a BMI of 30.0 or higher is classified as obesity. Obesity is further divided into Class I (BMI 30 to 34.9), Class II (BMI 35 to 39.9), and Class III (BMI 40 or higher).
Despite its widespread use, BMI has limitations because it does not distinguish between fat mass and lean muscle mass. Consequently, individuals with high muscle mass, such as athletes, may be misclassified as overweight or obese. Conversely, older adults who have lost muscle may have a normal BMI but still carry excess body fat.
To create a more complete health assessment, clinicians use other measurements alongside BMI. Waist circumference is a valuable indicator of abdominal, or visceral, fat, which is the fat stored around internal organs associated with a higher risk for heart disease and type 2 diabetes. A waist circumference greater than 40 inches for men and 35 inches for women is considered a risk factor. Body fat percentage, assessed through methods like DEXA scans, provides a more accurate picture of body composition.
The Complex Causes of Obesity
The development of obesity is a multifactorial condition where genetics, environment, behavior, and socioeconomic circumstances all contribute. Genetic predisposition plays a documented role in an individual’s susceptibility to weight gain. Research has identified numerous genes, such as variants in the FTO gene, that can influence appetite regulation, satiety, and the body’s tendency to store fat.
The modern environment is often described as “obesogenic” because it promotes obesity through the widespread availability of high-calorie, ultra-processed foods. Many communities lack access to affordable, nutritious options, leading to a greater reliance on convenience foods. Furthermore, urban design that prioritizes driving over walking can limit opportunities for daily physical activity.
Individual lifestyle and behavioral patterns are also significant contributors. Dietary habits high in processed foods and sugary beverages are a major factor, as is a sedentary lifestyle with prolonged periods of sitting. Insufficient sleep can also disrupt hormones that regulate appetite, such as ghrelin and leptin, leading to increased hunger and food intake.
Socioeconomic and psychological factors add complexity. Chronic stress is associated with an increased risk of obesity, as it can trigger the release of cortisol, a hormone that may increase cravings for high-fat, high-sugar foods. Lower levels of income and education are often correlated with higher rates of obesity, partly due to limited access to healthy foods, safe recreational spaces, and healthcare.
Systemic Health Consequences
The presence of excess body fat, particularly visceral fat, has far-reaching effects on nearly every system in the body. The physiological changes that accompany obesity disrupt normal bodily functions and create a state of low-grade, chronic inflammation.
The cardiovascular system is heavily burdened by obesity. Excess weight increases total blood volume, forcing the heart to work harder, which can lead to high blood pressure (hypertension). Obesity also promotes the buildup of fatty plaques in the arteries (atherosclerosis), which restricts blood flow and increases the risk of heart attacks and strokes.
In the endocrine system, obesity is a primary driver of insulin resistance. Adipose tissue releases inflammatory molecules that interfere with insulin’s ability to regulate blood sugar. This resistance forces the pancreas to produce more insulin, which can eventually lead to the exhaustion of insulin-producing cells and the development of type 2 diabetes.
The musculoskeletal system is also affected through increased mechanical stress on weight-bearing joints like the knees, hips, and lower back. This stress accelerates the wear and tear of cartilage, which can lead to osteoarthritis, a degenerative joint disease characterized by pain and reduced mobility. Obesity also impacts the respiratory system, as fat deposits in the neck can narrow the upper airway and lead to obstructive sleep apnea.
There is a well-established link between obesity and an increased risk for developing certain types of cancer. Excess adipose tissue can produce high levels of hormones like estrogen and growth factors that promote the growth of cancer cells. Cancers associated with obesity include those of the breast, colon, endometrium, kidney, and esophagus.
An Overview of Treatment Strategies
Managing obesity involves a spectrum of strategies tailored to an individual’s health profile, with the goal of achieving a healthier weight to reduce health risks. A 5% to 10% reduction in initial body weight can produce significant health benefits. The cornerstone of treatment is lifestyle modification, which integrates dietary changes, physical activity, and behavioral therapy. This approach focuses on creating a sustainable calorie deficit, aiming for at least 150 minutes of moderate-intensity exercise per week, and developing coping strategies for long-term success.
For individuals who do not achieve sufficient weight loss through lifestyle changes alone, pharmacotherapy may be an option. Medications are used as an adjunct to diet and exercise, not as a replacement. A prominent class of drugs is the glucagon-like peptide-1 (GLP-1) receptor agonists, such as semaglutide and liraglutide, which work by signaling satiety to the brain and helping regulate blood sugar.
In cases of severe obesity (a BMI of 40 or higher, or 35 with serious comorbidities), bariatric surgery may be considered. These procedures work by either restricting the amount of food the stomach can hold or altering the body’s ability to absorb nutrients. Common procedures include the sleeve gastrectomy, which removes a large portion of the stomach, and the Roux-en-Y gastric bypass, which creates a small stomach pouch and reroutes the small intestine.