In addition, the researchers found that the rats on the junk food diet grew large numbers of tumors throughout their bodies by the end of the study. Those on the more nutritious diet had fewer and small tumors that were not as widespread.

Blaisdell, 45, changed his diet more than five years ago to eat "what our human ancestors ate." He avoids processed food, bread, pasta, grains and food with added sugar. He eats meats, seafood, eggs, vegetables and fruits, and he has seen dramatic improvements in his health, both physically and mentally.

"I've noticed a big improvement in my cognition," he said. "I'm full of energy throughout the day, and my thoughts are clear and focused."

An expert in animal cognition Blaisdell conducts research that addresses the relationship between health and lifestyle (diet and exercise) and the relationship between a junk food diet and cognitive impairments it may induce.

"We are living in an environment with sedentary lifestyles, poor-quality diet and highly processed foods that is very different from the one we are adapted to through human evolution," he said. "It is that difference that leads to many of the chronic diseases that we see today, such as obesity and diabetes."

Co-authors of the research are Yan Lam Matthew Lau, Ekatherina Telminova and Boyang Fan, UCLA undergraduate students in Blaisdell's laboratory; Hwee Cheei Lim, the manger of Blaisdell's lab; Cynthia D. Fast, a UCLA graduate student in the lab; Dennis Garlick, a postdoctoral scholar in the lab; and David Pendergrass, a biology professor at the University of Kansas.

The research was funded by the National Science Foundation and by entrepreneur Cameron Smith.