Obesity has been more precisely defined by the National Institutes of Health (the NIH) as a BMI (Body Mass Index) of 30 and above. (A BMI of 30 is about 30 pounds overweight.) The BMI, a key index for relating body weight to height, is a person's weight in kilograms (kg) divided by their height in meters (m) squared.

Obesity:
Obesity is a medical condition characterized by an excessive accumulation of body fat, to the point where it can have a negative impact on a person's health. It is typically measured using the body mass index (BMI), which takes into account a person's height and weight.

Causes of Obesity:
- Poor diet: Consuming high-calorie, low-nutrient foods such as fast food and sugary drinks can contribute to weight gain.
- Lack of physical activity: Sedentary lifestyles with little to no physical exercise can lead to weight gain and obesity.
- Genetics: Some people may be more predisposed to obesity due to genetic factors.
- Medical conditions: Certain medical conditions such as hypothyroidism or polycystic ovary syndrome can contribute to weight gain.

Health Risks of Obesity:
- Obesity is associated with a higher risk of developing chronic conditions such as heart disease, diabetes, and certain types of cancer.
- It can also lead to psychological issues such as low self-esteem and depression.
- Obesity can put strain on the joints, leading to conditions like osteoarthritis.
- Sleep apnea and respiratory problems are more common in obese individuals.

Prevention and Treatment:
- Eating a balanced diet rich in fruits, vegetables, lean proteins, and whole grains can help prevent obesity.
- Regular physical activity is essential for maintaining a healthy weight and reducing the risk of obesity.
- Behavioral therapy, medication, and in severe cases, surgery may be recommended for the treatment of obesity.
Overall, obesity is a complex condition influenced by a combination of genetic, environmental, and lifestyle factors. It is important to address obesity through a combination of healthy eating, regular exercise, and medical intervention when necessary to reduce the associated health risks.