Obesity drugmakers Arena Pharmaceuticals (NASDAQ:ARNA), VIVUS (NASDAQ:VVUS), and Orexigen Therapeutics (NASDAQ:OREX) are three of the mostly hotly debated stocks in the biotech space. The fact that obesity afflicts more than 35% of American adults today defines these companies' massive market opportunity. Investors may not completely understand the nuances of this complex disease, however. For instance, how do clinicians approach the treatment of obesity? Are medications actually an integral part of treatment, or are lifestyle changes more important? Can obesity be cured?

In order to shed light on these topics, Motley Fool health-care analyst Max Macaluso spoke with Dr. Domenica Rubino, a weight management expert and representative of The Obesity Society. In the following segment from their discussion, Dr. Rubino discusses how clinicians define obesity and what other conditions it can lead to.

The relevant video segment can be found between 0:00 and 1:24.

Max Macaluso: Hi, welcome to The Motley Fool. I’m Max Macaluso and today I’m joined by Dr. Domenica Rubino. Welcome.

Dr. Domenica Rubino: Hi, Max. Thank you.

Max: Dr. Rubino is a board-certified physician in obesity medicine, endocrinology, diabetes and metabolism, and internal medicine.

Dr. Rubino: Absolutely.

Max: Today you’re here as a representative of The Obesity Society.

Dr. Rubino: Yes. Thank you.

Max: Dr. Rubino, three of the most popular stocks that our audience follows are Arena, Vivus, and Orexigen. These are three companies that are either developing drugs for the treatment of obesity or already have FDA approved drugs. You’ve also been involved in some of the trials as a clinical investigator.

Today let’s start with a general question. What is obesity?

Dr. Rubino: Obesity is a condition in which we have excess fat -- excess fat cells. The concern about obesity is actually the fat that’s deposited around the abdominal organs, which is reflected in an increase in abdominal waist circumference.

That abdominal obesity actually is what causes problems and diseases. It contributes to heart disease, diabetes, high blood pressure, cholesterol, sleep apnea.

Max: Cancer as well.

Dr. Rubino: Cancer as well, osteoarthritis, liver disease, infertility issues... so it is actually a major health risk to have this excess abdominal weight.