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An inactive lifestyle and a poor diet are often viewed as huge contributors to obesity. In a new study, researchers examined the relationship between these two factors and obesity. They reported that being overweight could explain why people lead sedentary lifestyles and not the other way around.

The research team from the University of California, Los Angeles (UCLA) tested 32 female rats. The rats were randomly divided into two diet groups for six months. The first diet was called the standard diet that included unprocessed foods such as ground corn and fishmeal. The other diet was made up of several processed foods such as sugar. This diet acted as the junk food diet.

The researchers examined the rats at three months. They found that the rats in the junk food diet were all significantly heavier than the rats from the standard diet. The rats also underwent a performance test that involved pressing a lever for food or water. The researchers observed that the heavier rats had impaired performance. They had more difficulty pressing the lever and took longer breaks in between each press. This finding suggested that these rats experienced fatigue from eating a junk food diet.

At the six months point, the researchers switched the rats in the groups. They found that when the overweight rats started eating the standard diet for nine days, they did not lose weight or perform better on the lever tests. The leaner rats that ate the junk food diet for nine days also did not experience any changes. The researchers concluded that eating a junk food diet for a prolonged period of time could negatively affect weight and mental ability.

"Overweight people often get stigmatized as lazy and lacking discipline," UCLA researchers, Aaron Blaisdell said reported by Medical Xpress. "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."

The study was published in the journal, Physiology and Behavior.