A new study suggests belly fat may be a better predictor of heart disease than body mass index, or BMI. They found people with larger waistlines faced a higher risk of heart disease, even if their BMI was considered normal. The body mass index uses a simple formula combining a person's weight and height. A person with a body mass index between 18.5 and 24.9 is considered a normal weight. For someone 5 feet 6 inches tall, 155 pounds is considered overweight, while 186 pounds is obese.