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When a Carb's Not a Carb: The Net Carb Debate
Will counting net carbs help or hurt weight loss
efforts?
By
Jennifer Warner
Reviewed By Michael Smith, MD
WebMD Feature
When
is a carb not a carb? That's the question many
carb-conscious dieters are facing as they struggle
to keep their carb counts within the strict limits
recommended by Atkins and other low-carb diets.
In an effort to cash in on the low-carb craze,
food manufacturers have invented a new category
of carbohydrates known as "net carbs,"
which promises to let dieters eat the sweet and
creamy foods they crave without suffering the
carb consequences.
But the problem is that there is no legal definition
of the "net," "active," or
"impact" carbs popping up on food labels
and advertisements. The only carbohydrate information
regulated by the FDA is provided in the Nutrition
Facts label, which lists total carbohydrates and
breaks them down into dietary fiber and sugars.
Any information or claims about carbohydrate content
that appear outside that box have not been evaluated
by the FDA.
"These terms have been made up by food companies,"
says Wahida Karmally, DrPH, RD, director of nutrition
at the Irving Center for Clinical Research at
Columbia University. "It's a way for the
manufacturers of these products to draw attention
to them and make them look appealing by saying,
'Look, you can eat all these carbs, but you're
really not impacting your health, so to speak.'"
Although the number of products touting "net
carbs" continues to grow, nutrition experts
say the science behind these claims is fuzzy,
and it's unclear whether counting net carbs will
help or hurt weight loss efforts.
What's in a Net Carb?
The concept of net carbs is based on the principle
that not all carbohydrates affect the body in
the same manner.
Some carbohydrates, like simple or refined starches
and sugars, are absorbed rapidly and have a high
glycemic index, meaning they cause blood sugar
levels to quickly rise after eating. Excess simple
carbohydrates are stored in the body as fat. Examples
of these include potatoes, white bread, white
rice, and sweets.
Other carbohydrates, such as the fiber found
in whole grains, fruits, and vegetables, move
slowly through the digestive system, and much
of it isn't digested at all (insoluble fiber).
Also in this category of largely indigestible
carbohydrates are sugar alcohols, such as mannitol,
sorbitol, xylitol, and other polyols, which are
modified alcohol molecules that resemble sugar.
These substances are commonly used as artificial
sweeteners.
In calculating net carbs, most manufacturers take
the total number of carbohydrates a product contains
and subtract fiber and sugar alcohols because
these types of carbohydrates are thought to have
a minimal impact on blood sugar levels.
For
example, the label on PowerBar's new double chocolate
flavor "ProteinPlus Carb Select" bar
says it has "2 grams of impact carbohydrates."
The Nutrition Facts label on the product says
it has 30 grams of total carbohydrates.
Just below the nutrition facts box, the "impact
carb facts" box provided by the manufacturer
explains, "Fiber and sugar alcohols have
a minimal effect on blood sugar. For those watching
their carb intake, count 2 grams." That's
30 grams minus the bar's 27 grams of sugar alcohols
and 1 gram of fiber.
The Skinny on Sugar Alcohols
But researchers say the impact of sugar alcohols
on blood sugar levels and the body is not fully
understood, and they may also cause problems in
some people.
"There are some sugar alcohols that can raise
your blood sugar," says Karmally. "Certain
sugar alcohols do have a higher glycemic index,
and they still are not counted as carbohydrates
by these companies."
"When you tell a person 'net carbs' or 'impact
carbs,' it's very confusing," says Karmally.
"A person with diabetes may think, 'It's
fine for me to have as much as I want.'"
People with diabetes are advised to closely monitor
their intake of carbohydrates because their bodies
can't produce enough insulin to keep blood sugar
levels within a safe range.
"I think we should not misguide people and
make them aware that these sugar alcohols also
contribute calories," says Karmally. "Too
much of them can actually have a bad effect, and
some of them can also have a laxative effect."
Although sugar alcohols have been used in small
amounts in items like chewing gums for years,
researchers say little is known about the long-term
effects of consuming large amounts of these substances.
Registered dietitian Jackie Berning, PhD, says
she steers her patients against products containing
sugar alcohols for those reasons.
"I just don't know how they're going to react.
We've never put that much in," says Berning,
an associate professor of nutrition at the University
of Colorado at Colorado Springs. "Some are
going to get diarrhea, and some are going to have
gastrointestinal problems."
Calories
vs. Carbohydrates
Berning
says the larger issue she has with products that
tout a low "net carb" count is that
they also often contain a lot of calories.
"It's my guess that most people are restricting
carbohydrates because they want to lose weight,"
Berning tells WebMD.
"The point I think they're missing is that
you may have 2 net carbs in this bar but you've
also got 260 calories," she says referring
to double chocolate Powerbar. "I don't care
that it's only 2 net carbs. The thing is, have
you done enough exercise, have you balanced the
rest of your diet to put in 260 calories in that
bar -- whether it has 30 grams of carbohydrates
or 2?"
Rather than focus on what she calls "the
little c" of carbohydrates, Berning says
people interested in weight loss should focus
on the "big C"-- calories.
Karmally agrees and says terms like net carbs
shouldn't trick dieters into thinking, "This
is a free lunch, and I can have as much as I want,"
just because a food company says the impact or
net carbs are only so much.
"You lose track of the fact that foods have
calories, and what has impact on weight management
is the number of calories you consume and the
amount of exercise you do," says Karmally.
Earlier this year, the FDA's Obesity Working Group
also advocated a simple "calories count"
approach to battling obesity and helping people
make healthy food choices.
"Our report concludes that there is no substitute
for the simple formula that 'calories in must
equal calories out' in order to control weight,"
says FDA Acting Commissioner Lester Crawford in
a news release announcing the report.
In addition, the report recommended that the FDA
respond to requests to define terms such as "low,"
"reduced," and "free" carbohydrates
as well as provide guidance on use of the term
"net carbs." Several industry and consumer
groups as well as food manufacturers have petitioned
the FDA to set official "low carb" levels
as well as take action on "net carb"
claims.
Until the agency takes action on the carbohydrate
claim issue, experts say carb counters are probably
better off eating foods that are naturally low
in refined carbohydrates, such as fruits and vegetables,
rather than highly processed foods like snack
bars, pastas, and sweets that have had their natural
carbohydrates stripped away.
"Whole foods, like whole grains, fruits,
and vegetables, should be the foundation of diet,"
says Karmally. "Because if you miss out on
these foods, then you end up missing out on a
whole bunch of nutrients and antioxidants that
have a potential benefit on reducing the incidence
of chronic, degenerative diseases."
Published
Aug. 5, 2004.
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SOURCES: Wahida Karmally, DrPH, RD, director of
nutrition, Irving Center for Clinical Research,
Columbia University. Jackie Berning, PhD, RD,
associate professor of nutrition, University of
Colorado, Colorado Springs. FDA. News release,
FDA. News release, Center for Science in the Public
Interest. News release, Grocery Manufacturers
of America. Atkins Nutritionals Inc. PowerBar.
WebMD Feature: "What Does Low-Carb Really
Mean?" WebMD Medical News: "Atkins Food
Pyramid Aims to Clear Confusion."
©
2004 WebMD Inc. All rights reserved.
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