Newly produced Coca-Cola soft drink bottles on an assembly line at a Coca Cola bottling plant in Clamart, near France. - 

Soft drinks have had a rough go of it lately. New York tried to ban them. Many schools are getting rid of them. Both Coke and Pepsi have promoted diet soda as a healthier option. But the sugar substitutes in them may not be so great for you, either. Tomorrow Coca-Cola starts a new ad campaign in defense of aspartame.

Susan Swithers is a professor at Purdue. She recently looked at several big studies of people who drank diet soda over a period of 20 to 25 years and found that people who drink as little as one diet soda a day "have increases in the risk not only for overweight and obesity, but also for diseases like type II diabetes, coronary heart disease, metabolic syndrome, high blood pressure and stroke."

It's research like this that beverage consultant Tom Pirko says is shaking the foundation of America's soda belief system. "The real issue here is whether or not Americans still buy into the religion of soft drinks in general. "

Pirko believes that as long as we continue to see a shift away from the belief that soft drinks are wonderful, safe and pleasurable, the beverage industry will continue to go on the offensive. "They have to dig in now and dig in deeply to try and control this before Americans stop believing in soft drinks."

Coke's new ad campaign is designed to do just that. It points out that aspartame is one of the most studied ingredients on the planet and the FDA has approved its use in over 6,000 products.

What the industry is trying to do, says Pirko, "is create a psychological marker to say that we have the scientific evidence to say that aspertame in particular is regulated and has proven to be safe."

Diet soda sales are declining even faster than regular soda. Not only because of health concerns about aspartame, but because diet sodas simply aren't working for consumers, says Pirko. "They switch over to diet and yet their waistlines continue to expand."

Follow David Weinberg at @@randomtape