Researchers at the University of Colorado have discovered that obesity and insulin resistance may be tied to the fructose your body makes as well as to the fructose you eat.
In a study involving mice, they found that the metabolic conversion of glucose into fructose in the liver is a key step in the development of glucose-induced obesity, insulin resistance and fatty liver.
Obesity due to fructose content
There is no doubt that eating carbohydrates with a high glycemic index, such as glucose, causes weight gain and metabolic problems. In recent years, added sweeteners, such as high-fructose corn syrup and sugar (sucrose), have been identified as risk factors for obesity and insulin resistance. Previous studies have suggested that the risk of obesity and insulin resistance from added sugars may be due to the fructose content. However, the mechanism by which this occurs is not fully understood.
Mice convert glucose to fructose in liver
But this latest study reports that fatty liver and insulin resistance may also result from fructose produced in the liver from non-fructose-containing carbohydrates.
The research team reported that mice can convert glucose to fructose in the liver and that this conversion was critical for driving the development of obesity and insulin resistance in mice fed glucose.
“Our data suggests that it is the fructose generated from glucose that is largely responsible for how carbohydrates cause fatty liver and insulin resistance,” said one of the lead researchers, Dr Miguel Lanaspa, in a press release from the university.
Why high glycemic foods increase obesity
Professor Richard Johnson, Professor of Medicine and Chief of the Division of Renal Diseases and Hypertension at the School of Medicine and senior author of the research paper, said, “Our studies provide an understanding for why high glycemic foods may increase the risk for obesity and insulin resistance. While some of the weight gain is driven by the caloric content and the effects of stimulating insulin, the ability of high glycemic foods to cause insulin resistance and fatty liver is due in part to the conversion of glucose to fructose inside the body.
Fructose is not safe
“Ironically, our study shows that much of the risk from ingesting high glycemic foods is actually due to the generation of fructose, which is a low glycemic sugar. These studies challenge the dogma that fructose is safe and that it is simply the high glycemic carbohydrates that need to be restricted.”
As part of the study, the researchers created two types of mice that either cannot convert glucose into fructose or cannot degrade fructose in the liver. They then fed these mice a glucose-rich diet for 10 weeks. As opposed to their normal counterparts, both strains of mice were resistant to weight gain, did not develop fatty liver and had normal metabolic parameters.
The research was published online on 10 September 2013, ahead of print, in the journal Nature Communications.
