For purposes of this discussion, "commercial diet program" means a nationwide corporate-owned weight loss program. These are programs that advertise widely and are generally well-known to the American public. They offer a very polished and consistent program, they have medical advisors and nutritionists on staff so their advice and their products are usually very safe and usually effective. They are also, with one notable exception, rather expensive.
The programs I will discuss are the "big three": Weight Watchers, Jenny Craig and Nutri-System.