Ocean/Corbis

In the '80s and '90s, diet soft drinks lent new fizz to the soda wars.

Advertisements featuring the world's most famous athletes and sexiest supermodels touted beverages that offered great taste and fewer calories. America was hooked.

But new sales figures now suggest that America's love affair with diet soda may have lost its pop.

"We used to say, 'I'm drinking diet. It's fine.' But these days it's becoming a little bit of a guilty confession in my office," said nutritionist Rachel Bell, author of "Eat to Lose, Eat to Win."

Nowadays, she said, clients are more apt to say: "I eat generally OK but I have to confess I drink diet soda."

Related: If you haven't already, 10 reasons to give up diet soda

For nine straight years, sales of carbonated beverages have been dropping.

For the last three years, the dropoff in diet soda sales has been steeper than for regular soft drinks - zero and low-calorie beverages have been down nearly 7 percent in the last year, while regular, full-calorie soda has been down a little more than 2 percent, according to Wells Fargo research.

Related: Diet soda linked to heart attack and stroke risks

Researchers at the University of Texas Health Science Center in San Antonio found that test subjects who drank two or more diet soft drinks a day saw their waist lines grow five times faster than those who did not drink diet soda.

In August, Coca-Cola published its first ad defending diet sodas, specifically those containing sugar substitutes such as aspartame as sales of diet sodas plummeted and people turned to flavored water.

The company was on a campaign to re-assure people that artificial sweeteners are safe even though the Food and Drug Administration reviewed more than 200 studies (some industry funded) on aspartame in 2007 and found no reason to issue warnings or pull it from the market.

"Our industry believes in the soft-drink business and sees opportunity for continued innovation and growth," said the American Beverage Association.

The beverages seeing the biggest growth these days are energy drinks, as well as good, old-fashioned water.