The researchers conducted the study on 32 female rates. Half of the rats were given unprocessed foods in diet and the remaining were put on lower-quality foods for a period of six months. Unprocessed foods included fish meal and ground corn.
After three months the researchers found the rats who were eating junk food diet became obese where as those who ate unprocessed foods didn't. The researchers also found the rats who ate junk food were not able to press a lever for reward of food or water quickly. They took twice the time taken by thinner rats.
Lead author of the study, Aaron Blaisdell, said the finding shows lethargy may arise from consumption of junk foods. After six months researchers made the obese rats to eat nutritious food for nine days and made the reaming rats to eat junk food. It was seen the weight of obese rats did not improve and they performed the leer task same as before, and the thin rats remained thin and performed the task as before. This suggests long-term eating is to be blamed an d not short-term.