Obesity is caused by an energy imbalance where more calories are consumed than expended over time. This imbalance can be due to individual behaviors, environment, and genetics. Excess weight gain leads to health risks like hypertension, stroke, coronary artery disease, colon cancer, gallstones, diabetes, dyslipidemia, and liver disease. The risks of these conditions increase with higher BMI and waist circumference. Losing weight through diet and exercise can significantly reduce health risks.