14 DAY TRIAL // According to the conclusions of a new study conducted on unsuspecting lab rats, it would appear that being overweight is the reason why some people become tired and take on a sedentary lifestyle. Previously, studies have suggested that the reverse is true and that being sedentary or tired was more likely to make a person overweight or obese.
The study was conducted by investigators at the University of California in Los Angeles (UCLA), who were led by Aaron Blaisdell. The expert holds an appointment as a professor of psychology with the UCLA College of Letters and Science and is also a member of the Brain Research Institute at the university. Details of the work appear in the latest issue of the journal Physiology and Behavior.
In a series of experiments, scientists divided a group of 32 female rats into two subgroups, putting each on a different diet for a total of 6 months. The control group was fed ground corn and fish meal, which can be considered as standard, relatively unprocessed rat food. The test group was fed a proxy of the typical junk food diet consumed in the United States.
The food contained significant amounts of sugar and was of consistently lower quality than what rats in the control group received. After just three months, most of the 16 rats in the test group had become fatter than their peers, exhibiting significantly higher body-mass indexes. “One diet led to obesity, the other didn’t,” says Blaisdell.
He and his group argue in the new study that exposure to a junk food-like diet leads to fatigue. This was demonstrated via a series of tasks that the rodents had to perform (press a lever to receive food or water). In all instances when the task was given, fat rats took longer breaks more often than their peers in the lean group. In some cases, the breaks were about twice as long, PsychCentral reports.
After the original 6 months, researchers switched diets between the two groups. Even though they started being fed the more nutritious and healthy diet, rats in the test group were unable to return to their normal weight and did not exhibit any improvements in lever test performances. A similar result was observed for the control group.
The 16 rats that were fed good food for 6 months did not exhibit any noticeable changes in weight after 9 days of consuming the junk food diet. Their motivation to press the lever remained the same, the team adds. Blaisdell and his group interpret these results as implying that obesity and cognitive impairments are the result of a prolonged exposure to lousy diets, not of occasional binges.
“Overweight people often get stigmatized as lazy and lacking discipline. 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 adds.