Those who are trying to lose weight should stop reaching for "diet" foods according to new American research, which found that the high levels of sugar in the products could actually be having the opposite effect.
Carried out by the University of Georgia in the United States, the team of researchers fed a groups of rats a diet high in sugar but low in fat to imitate many popular diet foods.
Another group was fed a high-fat, high-sugar diet and a third group was given a balanced, "normal" diet.
After monitoring the rats for a four-week period, the team found that rather than lose weight thanks to the "diet" food, the rats on this diet actually increased body fat mass when compared to rats fed a balanced rodent diet.
The high-fat, high-sugar group also showed significant increases in body weight and body fat, and both high-sugar groups also displayed an increase in liver fat and when compared to the balanced diet group.
The increase in liver fat was particularly significant in the low-fat, high-sugar group, which the study's principal investigator, Krzysztof Czaja, warned "is a very dangerous situation, because the liver accumulating more fat mimics the effect of non-alcoholic fatty liver disease."
Non-alcoholic fatty liver disease is a condition caused by fat buildup in the liver, which can result in liver damage comparable to that caused by heavy alcohol use.
In addition, the team found that the low-fat, high-sugar and high-fat, high-sugar diets caused inflammation in the brain, with previous rat studies by Czaja showing that brain inflammation alters gut-brain communication, and can hinder the brain's ability to determine when one is full.
"The brain changes resulting from these unbalanced diets seem to be long term, and it is still not known if they are reversible by balanced diets," added Czaja.
"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."
The findings also build on Czaja's previous study which found that an unbalanced diet decreased bacterial diversity in the gut, and a low-fat, high-sugar diet increased gut bacteria that are associated with liver damage.
The study was published online in the journal Physiology and Behavior.