The three largest makers of diet soda are facing separate federal lawsuits alleging consumers were deceived into believing their beverages would help them lose or manage weight.

Scientific studies show the opposite to be true, and the controversial sweetner aspartame is the problem, the lawsuits say. CBS News reports the lawsuits were filed in federal court this week against Coca-Cola, PepsiCo and Dr Pepper Snapple Group.

The New York Post reports the lawsuits were filed by six soft drink lovers who say the diet soda products caused them weight gain.

The lawsuits say use of the word "diet" is what's misleading and untrue. An attorney behind the case, Abraham Melamed, told CBS News "it's one of the biggest consumer scams in the last 50 years."

Coca-cola representatives said in a statement the lawsuit is meritless and that Diet Coke truly has zero calories, making it in compliance with labels and marketing.

Dr Pepper Snapple also says the claims of the lawsuit have no merit.