Diet soda helps weight loss according to American Beverage Association

While the typical participant banned from drinking diet sodas lost 9 pounds over 12 weeks, those allowed to continue drinking diet soda lost, on average, 13 pounds in the same time period. That's a 4-pound difference.
Hill says that in his clinical experience, many people who have successfully lost significant weight "are heavy users of noncaloric sweeteners."
But why was the diet soda group more successful? The most likely reason is that this group had the easier task.
Cutting calories and boosting exercise takes a lot of willpower. Trying to simultaneously give up something else you regularly enjoy -- such as diet soda -- taxes your ability to stay the course. Most psychologists agree that our willpower is a limited resource.

No offense, but putting credence into a study that only lasted 3 months; resulted in little more than a pound a month difference in the two groups and was sponsored by the American Beverage Association is very short sighted.
The long term issues of drinking diet soda and using artificial sweeteners is well documented as it relates to both physical and psychological well being.

The negative impact of consuming sugar-sweetened

beverages on weight and other health outcomes has

been increasingly recognized; therefore, many people

have turned to high-intensity sweeteners like aspartame,

sucralose, and saccharin as a way to reduce the

risk of these consequences. However, accumulating evidence

suggests that frequent consumers of these sugar

substitutes may also be at increased risk of excessive

weight gain, metabolic syndrome, type 2 diabetes, and

cardiovascular disease. This paper discusses these findings

and considers the hypothesis that consuming

sweet-tasting but noncaloric or reduced-calorie food

and beverages interferes with learned responses that

normally contribute to glucose and energy homeostasis.

Because of this interference, frequent consumption of

high-intensity sweeteners may have the counterintuitive

effect of inducing metabolic derangements.

Artificial sweeteners produce the

counterintuitive effect of inducing

metabolic derangements

Susan E. Swithers

Department of Psychological Sciences and Ingestive Behavior Research Center, Purdue University, 703 Third Street, West

Lafayette, IN 47907, USA

Like other major corporations and industry associations, The American Beverage Association is attempting to protect the market that their members have spent considerable time and money cultivating .  It isn't illegal to attempt to sway public opinion nor is it a concern of theirs to outline all possible consequences regarding their products. You no doubt have heard the term "buyer beware".   Corporations are not ethical or unethical only the humans within the organizations are ethically bound. The layers of corporate veil conveniently shield the executives from looking beyond profits into the real harm their product may bring upon mankind. To that end, it would be wise for consumers to invest time into the nutritional choices they make and to keep in mind that the Snake promised not to bite the tortoise if he provide him safe passage across the creek.  How did that story turn out?