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Study explains why sugar makes us sick and fat

Kathleen Blanchard's picture
Fructose has opposing effects in the body, find researchers in mouse study.

Obesity and metabolic syndrome, which are linked to high consumption of sugar, is now better understood, thanks to a team of researchers who discovered how fructose is metabolized in the body. Scientists say fructose is broken down by an enzyme that exists in two forms; one makes you fat and causes diseases of the liver and Type 2 diabetes, while the other protects from the ravages of sugar. Scientists have found fructose plays a double role in the body.

In studies conducted on lab animals, Richard Johnson, MD, the senior author of the study and Chief of the Division of Renal Diseases and Hypertension at the University of Colorado School of Medicine and colleagues found one form of an enzyme metabolizes fructose in a way that leads to obesity, diabetes and other illnesses, while another form of the same enzyme metabolizes sugar to protect lab animals studied from weight gain and disease.

According to the finding, the first enzyme in fructose metabolism is fructokinase, which has two isoforms - A and C.

Mice lacking both fructokinase isoform A and C were found to be protected from metabolic syndrome, a group of conditions that increase the risk of heart disease, stroke and Type 2 diabetes from obesity, high cholesterol and triglyceride levels and central obesity.

In the study, rodents lacking only fructokinase A were prone to develop metabolic disorders.

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Fructokinase C, in contrast, has an affinity for fructose and breaks it down quickly for energy use at a cellular level. Mice

The authors explain fructokinase A protects against the effects of metabolic syndrome that comes from the action of fructokinase C.

Johnson said the finding may help explain why some individuals are more vulnerable to obesity from high sugar intakes. Sources of fructose include sucrose and high fructose corn syrup.

Johnson said in a press release, "These studies provide new insights into how fructose may contribute to the development of obesity and diabetes. In particular, the identification of contrasting roles for two enzymes that are involved in fructose metabolism was surprising and could be important in understanding why some individuals may be more sensitive to the metabolic effects of fructose than others."

The study, published in the Proceeding of the National Academy of Sciences (PNAS), supports past research that high sugar intake from sucrose and high fructose corn syrup is linked to the obesity epidemic as well as non-alcoholic fatty liver disease, which is becoming more prevalent and thought to precede Type 2 diabetes.

"Opposing effects of fructokinase C and A isoforms on fructose-induced metabolic syndrome in mice"
Takuji Ishimoto, et al, doi: 10.1073/pnas.1119908109
doi: 10.1073/pnas.1119908109

Image credit: Wikimedia commons