McDonald's is America's most popular restaurant, with the Wall Street Journal reporting that it generated over $23 billion worth of sales last year.

One major seller is McDonald's Filet-O-Fish, something the company describes as "pure temptation on a lightly steamed bun." However, it's no secret that the Filet-O-Fish contains things many Americans would prefer to avoid. 

Trans fats linked to heart problems and diabetes

That's according to a report published this month by The Daily Meal contributor Melissa Szaro, which pointed to the presence of hydrogenated soybean oil.

Harvard's School of Public Health explains that such trans fats have "been implicated in heart disease, stroke, diabetes, and other chronic conditions."

Livestrong quoted nutritionist Jennifer O'Donnell-Giles as saying that the ingredient helps a product "stay on the shelf for longer, and it creates a mouthfeel people like."

"That's my first red flag as an ingredient," O'Donnell-Giles continued, adding, "It can be worse for you and hurt your heart health more than saturated fats."

Artificial colors may contribute to behavioral hyperactivity

The nutritionist also raised her eyebrow at McDonald's use of added colors, substances which the company is not required to describe.

"They don't have to tell you, but that brings up more questions when ingredients are randomly listed like that. It makes you think they have something to hide," O'Donnell-Giles said.

The Daily Meal pointed to a 2007 study which found that "[a]rtificial colors or a sodium benzoate preservative (or both) in the diet result in increased hyperactivity in 3-year-old and 8/9-year-old children in the general population."

O'Donnell-Giles also pointed to the presence of sugar, an ingredient that many consumers may not associate with fish sandwiches. "I'm not sure why they add it except because people enjoy sugar," she admitted.

Too much sugar can boost risk of heart disease

In addition to causing tooth decay and weight gain, the Mayo Clinic warns that eating sugary food also leads to increased triglycerides.

"Triglycerides are a type of fat in the bloodstream and fat tissue," the Mayo Clinic's website states. "Eating an excessive amount of added sugar can increase triglyceride levels, which may increase your risk of heart disease."

Another concern is Polysorbate 80, something Szaro describes as being "a synthetic compound derived from dehydrated sugar alcohol and fatty acids" which is " used to help reduce fat separation in a processed food product.

"While more research needs to be done, there are concerns about the safety of polysorbate 80 in food," Szaro stressed, saying that the compound's inclusion "doesn't make us salivate.