Why Fructose May Make You a Couch Potato

Fructose may be linked to weight gain, inactivity and body fat


From salt to trans fat, many ingredients have come under scrutiny by health experts. One such ingredient found in many common prepackaged foods is no exception.

A new study from the University of Illinois found that fructose may cause significant weight gain, physical inactivity and body fat deposits.

“Our study suggests that such levels of fructose can indeed play a role in weight gain, favor fat deposition, and also contribute to physical inactivity," said Justin S. Rhodes, PhD, of Beckman’s NeuroTech Group and professor of psychology at the University of Illinois, in a press release. "Given the dramatic increase in obesity among young people and the severe negative effects that this can have on health throughout one’s life, it is important to consider what foods are providing our calories.”

Fructose — sometimes known as fruit sugar — is a simple carbohydrate that occurs naturally in fruits and berries. High fructose corn syrup (HFCS) is made from corn starch. When corn starch is broken down, the end product is corn syrup — which is essentially 100 percent glucose (a simple sugar).

According to the US Food and Drug Administration (FDA), enzymes are then added to corn syrup to convert some of the glucose to fructose. This process creates HFCS. HFCS may be found in bread, other baked goods, yogurt, soft drinks and many other processed foods found on grocery store shelves.

Dr. Rhodes and team looked at two groups of mice for 77 days. One group of mice was fed a high-fructose diet — with 18 percent of their daily calories coming from fructose. The other group of mice was fed a high-glucose diet — with the same number of calories coming from glucose. Both groups had the usual intake of calories for a mouse.

The high-fructose diet was intended to mimic the average intake of fructose of adolescents in the US, according to these researchers.

Dr. Rhodes and team found that the high-fructose mice had an increased body weight, liver mass and fat mass — compared to the high-glucose mice. Researchers also found that the high-fructose mice became less active.

"Biochemical factors could also come into play in how the mice respond to the high fructose diet," said study author Jonathan G. Mun, in the press release. "We know that contrary to glucose, fructose bypasses certain metabolic steps that result in an increase in fat formation, especially in fatty tissue and liver."

The FDA has not placed a warning on fructose. However, the FDA recommends everyone limit consumption of all added sugars, including HFCS.

This study was published April 20 in the journal Nature.

The Center for Nutrition, Learning and Memory funded this research. No conflicts of interest were disclosed.