Eating two and a half times more calories than the recommended daily allowance regularly will undoubtedly lead to obesity, but it can also lead to diabetes, heart disease and even cancer.

That’s what a new study conducted by a research team led by Guenther Boden and Salim Merali from Temple University revealed. The study had six healthy male participants consuming 6,000 calories’ worth of food every day for a week while laying in bed and not engaging in any sort of movement or exercise. Merali told New Scientist:

“It was a regular, American diet, composed of pizzas, hamburgers and that sort of thing.”

Within two days of their diet, all of the volunteers developed resistance to the hormone insulin. After a week, they had gained an average of seven and a half pounds.

Resistance to insulin is known to threaten the health of the kidneys, nervous system and heart, and can lead to diabetes. Francis Stephens at the University of Nottingham in the UK told New Scientist:

“By definition, they all developed diabetes.”

The team also noticed that the volunteers were urinating increasing amounts of oxidised lipid compounds as the week progressed, which is commonly seen in individuals who have oxidative stress.

Oxidative stress weakens blood sugar regulation, which alters the structure of a protein that is usually in charge of moving glucose out of the bloodstream. This results in glucose not being removed from the blood.

While other mechanisms are probably still involved, the researchers pointed at oxidative stress and a damaged glucose-transporting protein as the potential causes for type 2 diabetes and obesity.

Stephens said that the participants’ seven-pound weight gain in a week is severe. He added:

“It will probably take them several months to get rid of it.”