We’ve all felt like a sloth after eating an entire bag of chips. But in the world of nutrition research, an age-old chicken-and-egg debate still rages on: Does eating junk food make you lazy, or does laziness make you eat junk food?
New research from UCLA points to the former. Eating sugary, processed, and high-fat foods can actually cause tiredness, a lack of motivation and decreased performance, according to a study published in the April 10 issue of Physiology & Behavior.
Thirty-two female rats were placed on one of two diets for six months. The first was a standard (read: healthy) rat’s diet of unprocessed foods like ground corn and fish meal. The second was made up of highly processed foods that included substantially more sugar, similiar to a human junk food diet. After three months, the 16 rats on the junk food diet became much fatter than the others—no surprise there.
But they got lazier too.
As part of the study, the rats were given a task in which they were required to press a lever to receive a food or water reward. The rats on the junk food diet demonstrated impaired performance, taking longer breaks than the lean rats before returning to the task. In a 30-minute session, the overweight rats took breaks that were nearly twice as long as the lean ones.
After six months, the rats’ diets were switched, and the overweight rats were given the more nutritious diet for nine days. This change, however, didn’t help reduce their weight or improve their responses. The reverse was also true: Placing the lean rats on the junk food diet for nine days didn’t increase their weight noticeably or result in any reduction in their motivation on the lever task. These findings suggest that a pattern of consuming junk food, not just the occasional binge, is responsible for obesity and cognitive impairments, lead researcher Aaron Blaisdell said.
So, do people who are overweight become less healthy or do less healthy people become overweight?
“Overweight people often get stigmatized as lazy and lacking discipline,” says Blaisdell. “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.”
Blaisdell, 45, is practicing what he’s preaching. He changed his diet more than five years ago to avoid 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.”
The opposite of a sloth.