UC DAVIS (US) — A fructose-heavy diet may contribute to the development of metabolic syndrome—which can increase the risk of developing cardiovascular disease and diabetes.
The findings, published online in the journal Nutrition & Metabolism, come from a University of California, Davis, study that investigated the relative effects of fructose or glucose consumption on 32 older, overweight or obese men and women.
The study participants consumed glucose- or fructose-sweetened beverages, which provided 25 percent of their energy requirements for 10 weeks.
Consumption of fructose, but not glucose, affected various parameters associated with metabolic syndrome, including increased circulating concentrations of uric acid, which is known to be higher in people with metabolic syndrome.
In addition, fructose consumption increased GGT activity, which is an indicator of liver dysfunction, and production of a type of protein known as RBP-4, associated with increased insulin resistance.
No previous studies have investigated the effects of glucose or fructose consumption on circulating levels of RBP-4.
The study design involved three phases, including a two-week inpatient baseline period, an eight-week outpatient intervention period, and a two-week inpatient intervention period.
During baseline, subjects resided in the UC Davis Clinical and Translational Science Center’s Clinical Research Center (CCRC) for two weeks before beginning the outpatient intervention, consuming either fructose- or glucose-sweetened beverages. They returned to the CCRC for the final two weeks of intervention.
Fasting and 24-hour blood collections were performed at baseline and following 10 weeks of intervention for measurement of plasma concentrations of uric acid, RBP-4, and liver enzyme activities.
The study’s first results, published in 2009, showed that visceral adipose volume (fat inside the abdominal cavity) was significantly increased only in subjects consuming fructose, along with increases in several circulating lipids and a decrease in insulin sensitivity, although both groups exhibited similar weight gain.
Fruit vs. juice
Glucose and fructose are both simple sugars, and equal parts of each are the recipe for table sugar—sucrose. The pure glucose and fructose that were used to sweeten the beverages in this study are not found in nature. Most fruits and honey contain comparable amounts of glucose, fructose, and sucrose.
Grains such as wheat, oats, corn and barley contain large amounts of glucose (and negligible amounts of fructose), but the glucose is packaged as long chains that are called starch or complex carbohydrate.
Co-author Lars Berglund, director of the UC Davis Clinical and Translational Science Center, points out that fruit juices typically feature more concentrated forms of these sugars, while fruits and vegetables contain fiber and other beneficial components.
“It’s healthier to eat apples than to drink apple juice,” says Berglund.
Senior author Peter Havel, a UC Davis professor with joint appointments in the Department of Molecular Biosciences in the School of Veterinary Medicine and the Department of Nutrition, is currently the principal investigator for a follow-up study comparing impacts of glucose, fructose, and high-fructose corn syrup in younger patients. His colleague and collaborator, Kimber Stanhope, directed and coordinated the clinical research study.
Other authors include researchers from UC Davis, Touro University, Vanderbilt University, and the US Department of Agriculture.
This research was supported with funding from National Institutes of Health, the NIH’s National Center for Research Resources, and the NIH Roadmap for Medical Research.
Havel’s laboratory receives support from the NIH and a Multicampus Award from the University of California, Office of the President, and Keim’s research is supported by intramural US Department of Agriculture-Agricultural Research Service Current Research Information System.
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