Fructose -- Found In High-fructose Corn Syrup, Sugar -- Sets Table For Weight Gain Without Warning
too much fructose can induce leptin resistance, a condition that can
easily lead to becoming overweight when combined with a high-fat,
high-calorie diet, according to a new study.
previous studies have shown that being leptin resistant can lead to
rapid weight gain on a high-fat, high-calorie diet, this is the first
study to show that leptin resistance can develop as a result of high
fructose consumption. The study also showed for the first time that
leptin resistance can develop silently, that is, with little indication
that it is happening.
study was carried out by Alexandra Shapiro, Wei Mu, Carlos Roncal,
Kit-Yan Cheng, Richard J. Johnson and Philip J. Scarpace, all at the
University of Florida College of Medicine in Gainesville.
is a hormone that plays a role in helping the body to balance food
intake with energy expenditure. When leptin isn’t working –
that is, when the body no longer responds to the leptin it produces
– it’s called leptin resistance. Leptin resistance is
associated with weight gain and obesity in the face of a high-fat,
has been a growing problem in the U.S. and in other parts of the world
and fructose has been suspected of playing a role. Fructose is the
sugar found in fruit, but it’s not the normal consumption of
fruit that is the problem. Table sugar and high-fructose corn syrup are
about 50% fructose and these ingredients have become increasingly
common in many foods and beverages. With sugar and high-fructose corn
syrup being added to many foods, people now eat much more fructose than
University of Florida researchers hypothesized that a high-fructose
diet could lead to leptin resistance, which in turn could lead to
exacerbated weight gain in the face of a high-fat, high-calorie diet, a
typical diet in industrialized countries. To test their hypothesis, the
research team performed a study with two groups of rats. They fed both
groups the same diet, with one important exception: one group consumed
a lot of fructose while the other received no fructose.
these six months, there were no differences in food intake, body
weight, and body fat between rats on the high-fructose and the rats on
the fructose-free diets. In addition, there was no difference between
the two groups in the levels of leptin, glucose, cholesterol or insulin
found in their blood. There was only one difference at the end of the
six months: The rats on the high-fructose diet had higher levels of
triglycerides in their blood.
researchers next tested the animals to see if they were leptin
resistant. They injected all the animals with leptin, to see if they
would respond by eating less. Animals whose leptin response is
functioning normally will lower their food intake. The researchers
discovered that the rats on the high-fructose diet were leptin
resistant, that is, they did not lower their food intake when given
leptin. The no-fructose animals responded normally to leptin by eating
first six months of the study showed that leptin resistance can develop
silently. "Usually, leptin resistance is associated with obesity, but
in this case, leptin resistance developed without obesity," Shapiro
said. "This was very surprising."
seen that leptin resistance could develop silently, the researchers
next wanted to find out what would happen if they switched the rats to
a high-fat, high-calorie diet – the kind many Americans eat. They
found that the animals exposed to the high-fructose diet, the leptin
resistant rats, ate more and gained much more weight and fat than the
leptin responsive animals on the fructose-free diet. All told, this
study showed that leptin resistance can:
- develop by eating a lot of fructose
- develop silently, that is, with very little indication it is happening
- result in weight gain when paired with a high fat, calorie dense diet
said the study suggests it is the interaction between consumption of
large amounts of fructose-containing foods and eating a high-fat,
high-calorie diet that produces the weight gain. "This study may
explain how the global increase in fructose consumption is related to
the current obesity epidemic," Shapiro said.
researchers hypothesize that the elevation in triglycerides produced by
fructose prevented leptin from reaching the brain. If leptin does not
reach the brain, the brain will not send out the signal to stop eating.
presence of high fructose alters the way leptin works, fooling the
brain so that it ignores leptin," Scarpace said. Consumers should be
cautious about what they eat, checking labels to see how much sugar the
items contain, Shapiro said.
For more information on the American Physiological Society, www.the-aps.org.