Arena Pharmaceuticals (NASDAQ:ARNA) and VIVUS (NASDAQ:VVUS) both had obesity drugs approved by the Food and Drug Administration (FDA) in 2012, and are two of the most contentious stocks on the market today. The high rates of obesity in America underscore the potential opportunities these companies have, but investors may not completely understand how physicians actually treat this disease. For instance, are medications really a necessary part of treatment? Are lifestyle changes more important, and can obesity be cured?

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 video segment from their discussion, Dr. Rubino talks about how losing 5-10% of weight can have an important impact on an obese patient's health. A transcript follows the video.

The relevant video segment can be found between 12:33 and 13:57.

Max Macaluso: When you're looking at individual patients, how much weight loss -- in terms of the percentage of their total weight -- do you aim for?

Dr. Domenica Rubino: That's another misconception, and I think it has to do a lot with expectations. I think there's individual expectations and societal expectations that continually get reinforced by, "Oh, this person lost so much weight," and certain shows that show a person losing 16 pounds in one week. That's totally unrealistic.

What we do know from the field is losing 5%-10%, which sounds very low for most people, but 5%-10% of weight is associated with absolute improvement in metabolic conditions. It actually doesn't take much weight loss to effectively reduce medications for a given disease or improve disease.

The perfect example is diabetes. Both for treatment of diabetes, a weight loss between 5-10% allows reduction in medications, many times people can get off medications, and their diabetes is in much better control.

For prevention the DPP trial, the Diabetes Prevention Trial, showed that an average weight loss of 6.5%, which isn't much, actually reduced the rate of developing diabetes by 58%. All of the research consistently shows that a small amount of weight loss -- what we consider small -- actually produces large changes in terms of clinical benefit for people.

Max Macaluso, Ph.D., and The Motley Fool have no position in any of the stocks mentioned. Dr. Rubino was a clinical investigator for the obesity drugs developed by Arena Pharmaceuticals, VIVUS, and Orexigen Therapeutics, but she has no position in any of the stocks mentioned and no financial relationships with any of the companies mentioned.Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.