Coca-Cola (KO), PepsiCo (PEP) and the rest of the carbonated beverage industry can't afford to ignore Thursday's call by health activists and some cities for the U.S. Surgeon General to conduct a comprehensive study on the health effects of soda, much like the landmark report on the dangers cigarette smoking decades ago. Too much is at stake.

Soda is a convenient whipping boy in the battle against obesity because it is devoid of nutritional benefits. However, the link between soda and America's bulging waistlines is not clear cut. For instance, fewer people are drinking soda on a per-capita basis, a more than decade-long trend that the Center for Science and the Public Interest, the industry's fiercest critic, has applauded.

Moreover, diet soda's share of the market has been increasing, accounting for about 29% of soda sales volume in 2011 compared with 70.9% share for regular soda, according to Beverage Digest.

A Surgeon General study, if it ever happens, would examine all the soda health issues, but would be unfair if it stopped at regular soda. Though diet soda has the aura of being a healthier alternative to sugary carbonated beverages, it has its own set of problems. A study released last year found that daily drinkers of diet soda had a 61% higher risk of stroke, heart attacks and other "vascular events." Another study found that diet soda drinkers were more likely to gain weight.

A recent New York Times op-ed made a convincing case against the consumption of cow's milk. Fruit juice is no panacea either. "Like soda, it can contribute to energy imbalance. High intakes of juice can contribute to diarrhea, overnutrition or undernutrition, and development of dental caries," according to a 2001 study in Pediatrics. Energy drinks can be problematic as well.

The reasons why people get fat and stay fat are complex. Blaming one factor, such as soda consumption, misses the broad array of medical, economic and social factors that cause the problem. New York Mayor Mike Bloomberg's plan to limit soda sizes is not the answer, and neither are soda taxes. Such approaches avoid the issue of individual responsibility.

Let's hope that the debate over soda's health effects can be based on science instead of simple fixes or sensationalistic press releases.

Jonathan Berr does not own shares of the listed stocks. Follow him on Twitter@jdberr.