It's no secret that many obese people live in America. We have so many choices when it comes to our eating and drinking habits, and many times we make the wrong decisions for our health. We think drinking diet sodas can help us lose weight as an alternative to sugary drinks that we know are not good for us. If drinking diet beverages could hurt, these three stocks could hurt your portfolio even more.

A study from The American College of Cardiology (ACC) has linked diet drinks with death or heart disease; this may change the way that people feel about diet soda . The health drawbacks are becoming an increasingly large obstacle for diet beverage giants Coca-Cola (KO 0.63%) and Dr. Pepper Snapple (DPS), which derive most of their revenue from soda sales. PepsiCo (PEP 1.34%), another diet beverage giant that is affected by this study, only derives at least 25% of its revenue from soda sales.

Declining diets
Women who consume two or more diet beverages a day have a 30% higher chance of having a heart attack or other cardiovascular "event," and 50% of them are more likely to die than those women who infrequently touch such drinks, according to the study . Who knew that drinking something that is supposed to be safe could contribute to health failure, as the study suggests.

Keep in mind that the study does not suggest that the diet drinks themselves are killers -- many other factors contribute. The researchers only found an association between the diet drinks and these problems, so saying that diet drinks were the main cause of the problems would overstate the results of the study. But partly due to this study, sales of diet drinks will probably decline in 2014. 

Risks facing diet soda companies
What this could possibly mean for Coca-Cola, Dr. Pepper Snapple, and PepsiCo: drops in stock price, possible lawsuits, higher R&D expenses, and possible label-restricting expenses. A few of the risk factors that the beverage manufacturers list in their annual reports suggest that they have plans in place to combat such a scare.

Coca-Cola, Dr. Pepper Snapple, and PepsiCo's business, image, and reputation could suffer as a result of this study. Any negative feedback a company receives in regards to its product's quality and safety results in a drawback in its stock price. This type of study could force companies like these to add specified labeling, in turn creating higher expenses and a loss of sales for their affected products. Coca-Cola, Dr. Pepper Snapple, and PepsiCo could also face modifications from lawmakers that could augment their costs, as well as decreased consumer demand for their products.

In 2010 soft drinks took a hit but diet drinks didn't. In a list of 10 drinks by sales figures four diet sodas appeared on the list: Diet Coke was in second, Diet Pepsi was in seventh, Diet Mountain Dew was in eighth, and Diet Dr. Pepper was in ninth.

However, diet beverage sales, representing almost a third of America's soda sales, have been declining for the last three years according to the Wall Street Journal. Sales of Diet Coke fell 6.8%, while its counterpart Coca-Cola only fell 0.5%. Diet Pepsi and Diet Mountain Dew fell more than their regular counterparts in 2013 as well. PepsiCo will be hurt less than Coca-Cola and Dr. Pepper Snapple because PepsiCo does not depend on its soda sales as much as its rivals.

Foolish wrap-up
Besides a diet scare these companies have strong brands and they would not let their reputations be tarnished by a study that does not confirm that their products are dominant causes of death or disease. Investors have no reasons to panic about the recent study on diet soda; if anything, short-term pullbacks could provide buying opportunities for long-term investors.