A UC study provides new evidence that
drinking large amounts of beverages containing fructose adds body fat,
and might explain why sweetening with fructose could be even worse than
using other sweeteners.
Researchers allowed mice to freely
consume either water, fructose-sweetened water or soft drinks. They
found increased body fat in the mice that drank the fructose-sweetened
water and soft drinks--despite that fact that these animals decreased
the amount of calories they consumed from solid food.
This, says author Matthias Tschöp, MD,
associate professor in UC's psychiatry department and a member of the
Obesity Research Center at UC's Genome Research Institute, suggests
that the total amount of calories consumed when fructose is added to
diets may not be the only explanation for weight gain. Instead, he
says, consuming fructose appears to affect metabolic rate in a way that
favors fat storage.
"Our study shows how fat mass increases as a direct consequence of soft drink consumption," says Dr. Tschöp.
The research appears in the July 2005
issue of Obesity Research, the official journal of the North American
Association for the Study of Obesity (NAASO).
Consumption of sweetened foods and
beverages containing sucrose and high-fructose corn syrup--particularly
carbonated soft drinks and some juices and cereals--has been thought to
be a leading cause of obesity. A widely used sweetener derived from
corn, high-fructose corn syrup is similar to sucrose (table sugar) in
its composition, about half glucose and half fructose.
Dr. Tschöp's lab used novel body
composition analyzers that use magnetic resonance technology to
carefully monitor body fat in mice.
All the mice began the study at an
average weight of 39 grams. Those consuming the fructose-sweetened
water showed significant weight gain over the course of the study, with
an average final weight of 48 grams--compared with averages below 44
grams for the other groups--and gained about 90 percent more body fat
than the mice that consumed water only.
Total caloric intake was lower in the
mice that consumed the fructose-sweetened water than in the other
groups, except for the control animals provided with water only.
"We were surprised to see that mice
actually ate less when exposed to fructose-sweetened beverages, and
therefore didn't consume more overall calories," says Dr. Tschöp.
"Nevertheless, they gained significantly more body fat within a few
Results from an earlier study in humans
led by Peter Havel, DVM, PhD, an endocrinology researcher at the
University of California, Davis, and coauthored by Dr. Tschöp, found
that several hormones involved in the regulation of body weight,
including leptin, insulin and ghrelin, do not respond to fructose as
they do to other types of carbohydrates, such as glucose.
Based on that study and their new data,
the researchers now also believe that another factor contributing to
the increased fat storage is that the liver metabolizes fructose
differently than it does other carbohydrates.
"Similar to dietary fat, fructose doesn't
appear to fully trigger the hormonal systems involved in the long-term
control of food intake and energy metabolism," says coauthor Dr. Havel.
The researchers say that further studies
in humans are needed to determine if high-fructose corn syrup in soft
drinks is directly responsible for the current increase in human
This study was conducted at both UC and
the German Institute of Human Nutrition, in collaboration with the
University of California, Davis.