High-fat foods are often demonised when it comes to fighting obesity – but sugar-laden "diet" foods could be contributing to unwanted weight gain too.
Researchers from the University of Georgia found that rats fed on a diet high in sugar but low in fat – which imitates many popular diet foods – increased body mass when compared to rats on a balanced diet.
The study, published in the journal Physiology and Behavior, found high-sugar diet also caused a variety of other problems too, including brain inflammation and liver damage.
"Most so-called diet products containing low or no fat have an increased amount of sugar and are camouflaged under fancy names, giving the impression that they are healthy, but the reality is that those foods may damage the liver and lead to obesity as well," said the study's principal investigator, Krzysztof Czaja.
"What's really troubling in our findings is that the rats consuming high-sugar, low-fat diets didn't consume significantly more calories than the rats fed a balanced diet," Czaja said.
"Our research shows that in rats fed a low-fat, high-sugar diet, the efficiency of generating body fat is more than twice as high – in other words, rats consuming low-fat high-sugar diets need less than half the number of calories to generate the same amount of body fat."
Over a four-week period, researchers monitored the body weight, calorie intake, body composition and fecal matter of three groups of rats. One group consumed a diet high in fat and sugar, another was fed a low-fat and high-sugar diet and a third group was given a "normal" diet.
Both the low-fat, high-sugar and high-fat, high-sugar groups displayed an increase in liver fat and significant increases in body weight and body fat, compared to the balanced diet group.
The liver fat accumulation was significant in the high-sugar, low-fat group, which according to the researchers, mimicked the effect of non-alcoholic fatty liver disease. It can result in liver damage comparable to that caused by heavy alcohol use.
The unbalanced diets also induced chronic inflammation in the brain.