They singled out a few particular gut-busting dishes -- the sort of food found on the menu at franchises across the country.
"These huge portion sizes can not only blow your diet for the day but can blow your diet for the week," said Margo Wootan, director of nutrition policy for the Center for Science in the Public Interest.
We wanted to see what effect eating this food would have on our bodies, other than the obvious impact on our waistlines.
ABC News producer Jon Garcia and I went to the University of Maryland Medical Center to put an appetizer, entree and dessert to the test.
Before we ate, researchers took blood samples and gauged the health of our arteries with an ultrasound. We both passed the tests and were deemed perfectly healthy.
Our three-course meal: an appetizer (deep fried macaroni and cheese), entree (quesadilla burger) and dessert (mega-sized deep dish sundae) packed 6,190 calories and 187 grams of saturated fat. The USDA recommends that adults our age eat roughly 2,000 calories per day, and no more than 20 grams of saturated fat. This means our single meal packed more than three times the daily recommended calories, and nearly 10 times the saturated fat suggested by federal guidelines.
We tried our best, but neither Jon nor I could finish the massive portions. We both felt tired and sluggish after eating. Jon even got a severe headache.
Gut-Busting Meals Have Immediate Impact
We waited two hours, then it was time to test our blood. Jon's blood samples showed an obvious, significant difference. While his pre-meal blood sample was relatively clear, his post-meal sample was extremely cloudy -- you could literally see the fat that was now flooding his system.
My blood also showed a difference, though not nearly as dramatic as Jon's. On the other hand, my ultrasound revealed a startling change. A large dose of saturated fat causes a chemical reaction, wherein the arteries narrow and do not dilate properly. This means the heart must work harder to pump blood through the arteries. In my case, my heart was working so intensely to pump blood through my narrowed arteries, you could actually hear the difference in my blood flow.
The University of Maryland's Dr. Robert Vogel and Dr. Michael Miller analyzed our results. They both agreed that the food had made a major impact.
"It shows that one meal can affect the health of your arteries," said Vogel. "Each and every meal is important to the health of our arteries and since we live by our arteries, your survival depends on it."
Miller said that eating high-fat foods like the ones Jon and I did is as bad as smoking cigarettes.
"You are developing premature aging of your vascular system by eating an unhealthy diet," Miller explained.
Although the scary effects of our one enormous meal lasted just six hours, doctors warn that if eaten regularly, these types of unhealthy meals can lead to heart attacks and a variety of other health problems.
"It's the poisoning of America. There's just no question about it. We have the best country on Earth, and we have a lousy lifestyle. We really do, and it starts with food," said Vogel.
ABC News' Brian Hartman contributed to this report.