In a study to understand why only some people gain weight and get health issues, researchers are paying people to consume an extra 1000 calorie fast food meal a day for three months.

Researchers at the Washington University School of Medicine in St. Luis are paying individuals to eat the extra fast food meal in order to find out why some people gain weight and develop health issues like diabetes and hypertension while other people do not develop the same issues.

Five fast food restaurants will participate in the study including Burger King, Taco Bell, Pizza Hut, KFC and McDonalds.

The pay scale for the participants is incentivized.

"Participants can earn up to $3,500, depending on how long it takes them to reach the study's weight goal. They have to gain 5-6% of their body weight during the three-month span. Researchers monitor their weight from week to week. After the study, the hospital guides participants through weight loss back to their baseline," LA Weekly reported.

Dr. Samuel Klein is the lead researcher in the study and he said to ABC News, "What you learn in rodents does not always translate to people. What you learn on flies and worms won't translate to people."

ABC News reported that Fast Food restaurants are good at regulating food content and it researchers know the amout of calories and nutrition content in each meal. Klein added to ABC News, We know exactly the calories and macro-nutrient composition within fast food restaurants, so it's a very inexpensive, easy and tasteful way to give people extra calories."