Dr. Elizabeth Parks of the University of Texas Southwestern Medical Center in Dallas said fructose, glucose and sucrose are all forms of sugar but are metabolized differently. Fructose, a monosaccharide, or simple sugar, is naturally found in high levels in fruit and is also added to many processed foods.

"All three can be made into triglycerides, a form of body fat; however, once you start the process of fat synthesis from fructose, it's hard to slow it down," Parks said in a statement.

In humans, it is the liver's job, when it encounters glucose, to decide whether the body needs to store the glucose as glycogen, burn it for energy or turn the glucose into triglycerides. However, fructose enters this metabolic pathway downstream, bypassing the liver and flooding the metabolic pathway.

"It's a less-controlled movement of fructose through these pathways that causes it to contribute to greater triglyceride synthesis," Parks said. "The bottom line of this study is that fructose very quickly gets made into fat in the body."

The findings are published in the Journal of Nutrition.