Fructose May Make You Fatter
Study: Simple Sugar Turns to Fat With “Surprising Speed”
July 31, 2008 -- Dieters know to limit their sugar intake, but new research
suggests that not all sugars are equal when it comes to packing on the
Research from the University of Texas Southwestern Medical Center (UTSW)
shows that the body turns fructose into fat more efficiently than it does other
"Our study shows for the first time the surprising speed with which
humans make body fat from fructose," lead author Elizabeth Parks, PhD, of
UTSW's Center for Human Nutrition.
The findings might be interpreted as confirmation that high-fructose corn
syrup -- the much maligned sweetener added to many processed foods -- really
does cause more weight gain than the other sugars
But it isn't that simple. Not by a long shot.
Sugars: Fructose, Glucose, and Sucrose
Parks and her research team studied the simple sugar fructose, not
high-fructose corn syrup or sucrose, which are a mix of fructose and
Just about all the sugar we eat in foods, including those in fruits, contain
some fructose and glucose.
"The goal was not to test the effects of high-fructose corn syrup,"
Parks tells WebMD. "The study didn't address that."
Instead, the researchers wanted to find out if fructose is more likely to
lead to fat development than glucose.
They did this by feeding six healthy people breakfast drinks containing
three different sugar combinations followed by a carefully controlled lunch
over several weeks.
In one test, the breakfast drink contained 100% glucose, similar to the oral
glucose test doctors give when they suspect diabetes. In another, the drink
was half glucose and half fructose, and in the third, the drink was 25% glucose
and 75% fructose.
The researchers measured the conversion of the sugars to fat in the liver
and how the morning sugar meal influenced the metabolization of foods eaten
later in the day.
They found that lipogenesis -- the process by which sugars are turned to
body fat -- increased significantly when the breakfast drinks contained
In addition, the study suggested that when fructose is eaten with fat or
before fat is consumed, the fat is more likely to be stored rather than burned,
Parks explains that the liver tends to act like a traffic cop for glucose,
determining whether glucose will be burned for energy or stored as fat.
Fructose, on the other hand, seems to bypass the process.
"Fructose gets made into fat more quickly, and when that process is
turned on there seems to be a signal that goes to the liver that says store all
the other fats you are seeing," she says.
Fruit OK, Added Sugars Aren't
Although it would be almost impossible to avoid fructose without eliminating
all sweet and sweetened foods from your diet, it is clear that not all
foods containing fructose are equal, says nutritionist Lona Sandon, RD, who is
with UTSW but did not work on the study.