Boosting Weight Loss By Limiting Fructose
One of the reasons people on low-carbohydrate diets may
lose weight is that they
reduce their intake of fructose, a type of
sugar that can be made into
body fat quickly, according to a researcher at UT Southwestern Medical Center.
Dr. Elizabeth Parks, associate professor of clinical nutrition and lead author
of a study appearing in a current issue of the Journal of Nutrition, said
her team's findings suggest that the right type of
carbohydrates a person eats
may be just as important in weight control as the number of
calories a person
Current health guidelines suggest that limiting processed carbohydrates, many of
which contain high-fructose corn syrup, may help prevent weight gain, and the
new data on fructose clearly support this recommendation.
The study shows for the first time the surprising speed with which humans make
body fat from fructose. Fructose, glucose and sucrose, which is
a mixture of fructose and glucose, are all forms of sugar but are metabolized
differently. According to the study, all three can be made into triglycerides, a form of
body fat; however, once you
start the process of fat synthesis from fructose, it's hard to slow it down.
triglycerides are predominantly formed in the liver, which acts like
a traffic cop to coordinate the use of dietary sugars. It is the liver's job,
when it encounters glucose, to decide whether the body needs to store the
glucose as glycogen, burn it for energy or turn the glucose into triglycerides.
When there's a lot of glucose to process, it is put aside to process later.
Fructose, on the other hand, enters this metabolic pathway downstream, bypassing
the traffic cop and flooding the metabolic pathway. It's a less-controlled
movement of fructose through these pathways that causes it to contribute to
greater triglyceride synthesis. The bottom line of this study is that
fructose very quickly gets made into fat in the body.
Though fructose, a monosaccharide, or simple sugar, is naturally found in high
levels in fruit, it is also added to many processed foods. Fructose is perhaps
best known for its presence in the sweetener called high-fructose corn syrup or HFCS, which is typically 55 percent fructose and 45 percent glucose, similar to
the mix that can be found in fruits. It has become the preferred sweetener for
many food manufacturers because it is generally cheaper, sweeter and easier to
blend into beverages than table sugar.
The Research Study
For the study, six healthy individuals performed three different tests in which
they had to consume a
fruit drink formulation. In one test, the
was 100 percent glucose, similar to the liquid doctors give patients to test for
diabetes - the oral glucose tolerance test. In the second test, they drank half
glucose and half fructose, and in the third, they drank 25 percent glucose and
75 percent fructose. The tests were random and blinded, and the subjects ate a
regular lunch about four hours later.
The researchers found that lipogenesis, the process by which sugars are turned
into body fat, increased significantly when as little as half the glucose was
replaced with fructose. Fructose given at breakfast also changed the way the
body handled the food eaten at lunch. After fructose consumption, the liver
increased the storage of lunch
fats that might have been used for other
The message from this study is powerful because body fat synthesis was measured
immediately after the sweet drinks were consumed. The
carbohydrates came into the body as sugars, the liver took the molecules apart
like tinker toys, and put them back together to build fats. All this happened
within four hours after the fructose drink. As a result, when the next meal was
eaten, the lunch fat was more likely to be stored than burned.
This is an underestimate of the effect of fructose because these individuals
consumed the drinks while fasting and because the subjects were healthy, lean
and could presumably process the fructose pretty quickly. Fat synthesis from
sugars may be worse in people who are overweight or
obese because this process
may be already revved up.
Dr. Parks said that people trying to lose weight shouldn't eliminate fruit from
their diets but that limiting
containing the sugar may help.
Do not demonize fructose as the cause
of the obesity epidemic, it may be a contributor, but it's
not the only problem. We're
overeating fat, we're overeating protein; and we're overeating all
Foods With Fructose
There are many foods that contain fructose, says Shirley Schmidt, CDE, a
diabetes nutrition educator at William Beaumont Hospital in Royal Oak, Mich.
Fructose is a natural sugar found in many fruits and vegetables. Table sugar, or
sucrose, is half fructose and half glucose. And as a component of high-fructose
corn syrup, fructose is found in everything from soda to
fruit drinks, sports
beverages, chocolate milk, breakfast cereals, flavored and
dessert syrups and
toppings, baked goods, candy, jam, sweetened yogurt, and many other packaged
And while it may be true that you'll gain weight by eating too much of the
above fructose-filled foods, you'll gain weight if you eat too much of any food.
Remember, obesity is caused by a host of environmental, psychological, and
physiological factors. All macronutrient food ingredients --
proteins -- will contribute to
weight gain when consumed to
Limit your consumption of fructose-sweetened beverages and snack foods
just as you would any simple carb. Of course, cutting back your total calorie
intake wouldn't hurt either.
Keep your total carbohydrate intake to no more than 50% of your daily
diet, and make sure that most of those carbs come from
fiber-rich sources such
as whole grains and vegetables rather than added sugars or processed foods.
is a good way to limit your intake of fructose and
Avoid any packaged food product that lists as one of its first three
ingredients anything ending in "ose" -- the chemical suffix that indicates
To satisfy your sweet tooth, choose fruit instead -- "nature's candy".