Obese people are frequently criticized for being sedentary, or more bluntly put—lazy. It isn’t always a fair characterization and inactivity in the obese is often attributed to a variety of factors, not the least of which being their physical health and abilities. However, a new study published in the journal Physiology and Behavior indicates the very foods that lead to obesity could also cause laziness, showing obesity and inactivity are more complexly linked than previously thought.
According to a press release from UCLA, the study involved feeding rats one of two diets—either one considered “healthy” by the researchers (of fish meal and ground corn) or one made up of junk food, sugar, and processed carbohydrates.
Not surprisingly, the rats fed the junk food diet gained weight. But more than that, they also became lazy.
Part of the study required the rats to press a lever to gain access to food or water as a reward. The junk food rats were slower, acted impaired, and actually took breaks in between tasks. In 30-minute sessions, the rats fed junk food took breaks twice as long as the healthier rats.
“Overweight people often get stigmatized as lazy and lacking discipline,” lead researcher Aaron Blaisdell said. “We interpret our results as suggesting that the idea commonly portrayed in the media that people become fat because they are lazy is wrong. Our data suggest that diet-induced obesity is a cause, rather than an effect, of laziness. Either the highly processed diet causes fatigue or the diet causes obesity, which causes fatigue.”
Unfortunately, changing the diet produced no quick fix. After six months, the researchers switched diets. For nine days, the overweight rats were given the healthier diet, but it didn’t reduce their weight or improve their responses to the lever trials. The healthier rats, placed on the processed food diet, similarly saw no immediate change.
“These findings suggest that a pattern of consuming junk food, not just the occasional binge, is responsible for obesity and cognitive impairments,” according to UCLA.
Perhaps even more importantly than the fact that the unhealthy rats were lazier than the others, they developed a “large number of tumors throughout their body”. Though the healthier rats also developed tumors (common in rats in general), there were far fewer and smaller.
“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,” explained Blaisdell. “It is that difference that leads to many of the chronic diseases that we see today, such as obesity and diabetes.”
What’s worse, previous studies have found that the junk food plaguing grocery store shelves alters certain parts of your brain responsible for levels of hunger, thirst, and the body’s natural rhythms and cycles. In other words, processed foods and junk foods are addictive.