The surprising news about soda sales

Per-capita soda consumption rates have fallen to their lowest levels since about 1986, a sign that continued attacks by public health groups over the potential health risks posed by these products may be working.

At least, to a point: Data released this week by the trade publication Beverage Digest shows that some of the leading full-calorie beverages made by industry leaders Coca-Cola (KO) and PepsiCo. (PEP) outperformed their diet counterparts.

Market leader Coke posted a volume gain of 0.1 percent in 2014, its first increase in many years. Pepsi, which dethroned Diet Coke for the number two spot, saw a 1.8 percent decline. Diet Coke, which finished fourth, fell 6.6 percent while Diet Pepsi was seventh with a 5.2 percent decline.

The data surprised Michael Jacobson, the head of the Center for Science in the Public Interest, a leading critic of the soda industry, who told CBS MoneyWatch that it shows that people who quit drinking regular soda are taking a pass on the diet varieties as well.

"You would think that would be the easiest change to make," he said in an interview. "Over the last few years, sales of Diet Coke and Diet Pepsi have seriously eroded."

One reason for the decline in diet soda consumption has been the growing concern about the potential health effects of the commonly used sweetener aspartame. Beverage Digest Editor and Publisher John Sicher told CBS MoneyWatch that those concerns about the chemical, which is sold under the brands Equal and NutriSweet, are without justification.

"Aspartame in fact is a safe and good sweetener," Sicher said, adding that the Food & Drug Administration and its regulators in Europe have given the sweetener as clean bill of health.

The CSPI's Jacobson isn't sold on aspartame, and accused the U.S. government of "sticking its head in the sand" by disputing studies that showed a link between the sweetener and cancer. Nonetheless, he noted that there has been far less negative press about the health effects of diet soda compared with regular soda, where a plethora of studies have documented its potential health effects.

For instance, scientists have found that people who consume sugar-sweetened soft drinks regularly have a 26 percent greater chance of developing diabetes. Another study found that men who guzzled down these beverages had a 20 percent higher risk of having a heart attack or dying of one compared with their counterparts who avoided the stuff.

Coca-Cola, PepsiCo and other carbonated beverage companies are trying to develop alternative sweeteners using stevia, a plant found in the jungles of Paraguay and are hoping to find what Bloomberg News described as the "industry's holy grail -- a soda that tastes as good as the iconic colas, is sweetened naturally, and has zero calories."

Both Coca-Cola and PepsiCo. introduced mid-calorie drinks sweetened with stevia, called Coke Life and Pepsi True. They are mixed with cane sugar since stevia can leave a bitter after taste, a problem that is hampering its wider use. According to Sicher, these products are too new to have a statistically significant impact on the market.

Jacobson wants more testing of stevia, though he considers it to be safer than artificial sweeteners and urges consumers to avoid drinking all soda.

"Health officials, legislators, and other policy makers should escalate their efforts to further drive down consumption by supporting policies that decrease availability in public places, raising new taxes, requiring warning labels, and otherwise promoting water as the default drink," he said in a recent press release.

Officials from Coca-Cola and PepsiCo didn't immediately respond to requests for comment.