U of I study: Fructose metabolism more complicated than was thought

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Public release date: 9-Dec-2008

http://www.eurekalert.org/pub_releases/2008-12/uoia-oi120908.php

Contact: Phyllis Picklesimer

p-pickle@...

University of Illinois at Urbana-Champaign

U of I study: Fructose metabolism more complicated than was thought

A new University of Illinois study suggests that we may pay a price for

ingesting too much fructose. According to lead author Manabu Nakamura,

dietary fructose affects a wide range of genes in the liver that had not

previously been identified.

Chances are you consume quite a bit of fructose. Most Americans do—in

refined sugars such as sucrose or table sugar (which is half fructose)

and in high-fructose corn syrup, used in products as diverse as soft

drinks, protein bars, and fruit juice.

But many scientists believe that high dietary fructose contributes to

the development of metabolic syndrome, a group of risk factors that

predict heart disease and Type 2 diabetes.

" For this reason, it's important for scientists to understand exactly

how consuming high amounts of fructose affects human health, " said

Nakamura, a U of I associate professor of food science and human nutrition.

Nakamura's lab is continuing to study the metabolism of fructose with an

eye to making recommendations about its dietary use.

His study shows that the metabolism of fructose is more complex than the

data had indicated. " Our gene-expression analysis showed that both

insulin-responsive and insulin-repressive genes are induced during this

process. Our bodies can do this, but it's complicated, and we may pay a

price for it, " he said.

According to the scientist, most carbohydrates are handled fairly simply

by our bodies. They are converted quickly to glucose and used for energy

or stored as fat. " When we are eating, blood sugar--and insulin

production--goes up. When we sleep or fast, it goes down, " he said.

The process is not so simple with fructose, he noted. " In order for

fructose to be metabolized, the body has to create both fasted and fed

conditions. The liver is really busy when you eat a lot of fructose. "

Because, unlike glucose, fructose metabolism occurs mainly in the liver,

Nakamura wanted to gain a complete picture of gene expression in the

liver during fructose metabolism.

In Nakamura's study, 24 rats were fed either a 63 percent glucose or

fructose diet four hours a day for two weeks; at the end of this period,

half the animals fasted for 24 hours before the scientists performed a

gene expression analysis; the other half were examined at the end of a

four-hour feeding.

Fructose feeding not only induced a broader range of genes than had

previously been identified, there were simultaneous increases in

glycogen (stored glucose) and triglycerides in the liver.

" To our surprise, a key regulatory enzyme involved in the breakdown of

glucose was about two times higher in the fructose-fed group than in the

glucose-fed group, " Nakamura said.

The study also suggests that a protein called carbohydrate response

element binding protein is responsible for the fructose effect on

certain genes that trigger the production of fat, he said.

" We're continuing to assess the risk of fructose insulin resistance and

the consequent risk for development of diabetes, " he said.

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Co-authors of the study, published in a recent issue of Biochimica et

Biophysica Acta, are Hyun-Young Koo, A. Wallig, Takayuki Y.

Nara, and B. H. Simon Cho of the University of Illinois and Byung Hong

Chung of the University of Alabama at Birmingham.

--

ne Holden, MS, RD

" Ask the Parkinson Dietitian " http://www.parkinson.org/

" Eat well, stay well with Parkinson's disease "

" Parkinson's disease: Guidelines for Medical Nutrition Therapy "

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