The
Basics About Carbohydrates
The three calorie-providing components of foods are carbohydrates,
protein, and fat. Carbohydrates are found in an immense variety
of foods. Which of these, for example, are rich sources of carbs:
orange juice, table sugar, nonfat milk, pears, strawberries,
whole-wheat bread, apple pie, popcorn, biscuits, green peas,
muffin, honey, sweet potatoes? If you chose all of these foods,
you're right. Carbohydrates (the word means carbon dioxide combined
with water) include all the sugars, starches, and fiber we eat.
Carbs (except for fiber) are transformed by the body into blood
sugar (mostly glucose), the body's basic fuel.
Carbohydrates are the main energy source for the body, and they're
the main source of calories in virtually every diet worldwide.
They supply 4 calories per gram, the same as protein. Fat has
more than twice as many calories (9 per gram)—one reason
for its bad reputation. Fiber, however, has no calories, because
it isn't absorbed by the body.
Since most carbohydrates are broken down into glucose, why does
it matter which carbohydrates you consume? Why is the energy
in a teaspoonful of sugar any better or worse than the equivalent
amount of carbs in lima beans or whole-wheat bread or, for that
matter, in a chocolate bar?
Not
so simple, not so complex
Most
carbohydrates come from plant-based foods—fruits, vegetables,
grains, and legumes (beans, peas, and lentils). Dairy products
are the only animal-derived foods with lots of carbs. There
are two general types of carbohydrates:
•
Simple carbohydrates
are sugars—glucose and fructose from fruits and some
vegetables, lactose from milk, sucrose from cane or beet sugar,
and others. Table sugar is pure sucrose. Much of the simple
carbs we eat are sugars added to processed foods such as sodas,
cookies, etc. These added sugars are the main reason why sugar
now accounts for 16% of all calories consumed by Americans;
20 years ago, it supplied 11%. Soda alone supplies about one-third
of this added sugar.
•
Complex carbohydrates,
which are chains of simple sugars, consist primarily of starches
as well as the fiber that occurs in all plant foods. Starch
is the storage form of carbohydrates in plants. Foods rich
in complex carbs include grains and grain products (such as
bread and pasta), beans, potatoes, corn, and some other vegetables.
Are complex carbs preferable to sugars?
Usually,
but not always. Many foods high in sugar (especially sucrose
and other added sugars) supply "empty calories"—that is,
they have few nutrients but lots of calories. By contrast, the
calories in foods rich in complex carbs usually bring many nutritional
extras with them. It depends on the food. Dairy products and
fruit contain sugars, but are important parts of a healthy diet
because of the other nutrients they contain.
Some foods rich in complex carbs are better than others. White
bread and french fries contain complex carbs, for instance,
but you can make better choices. Whole grains (such as oats,
whole wheat, brown rice) are more nutritious than refined grains,
since they retain the bran and the germ, which are rich in vitamins,
minerals, fiber, and beneficial phytochemicals. Whole grains
are digested more slowly, and thus have a more modest effect
on blood sugar than refined carbs or sugars (see below). The
same is true of vegetables and beans. The fiber in these foods
has many health benefits. In particular, soluble fiber (found
in oats, barley, and beans) may help lower LDL ("bad") cholesterol,
triglycerides, and blood pressure. In fact, people whose diet
is rich in whole grains and other high-fiber foods tend to have
a lower risk of heart disease, diabetes, and some cancers.
Carb bottom line
The
USDA's food pyramid is a good, practical place to start when
choosing your high-carb foods. It shows 6 to 11 daily servings
of grains, 2 to 4 servings of fruit, 3 to 5 servings of vegetables,
and 2 to 3 servings of dairy products (along with small amounts
of meat, poultry, or fish). The more calories you consume each
day, the more servings you should consume in each category.
Servings are small: just one slice of bread or a medium piece
of fruit; half a cup of cooked rice, pasta, beans, or vegetables;
a cup of raw leafy vegetables; or 3/4 cup of juice. A large
apple or banana, a cup of broccoli, or a medium-size salad each
counts as two servings.
Such a semi-vegetarian diet will derive more than half its calories
from carbs. But be choosy about what
kinds of carbs you pick—especially with those 6 to 11 grains.
You should include as many whole grains as you can (at least
3 servings a day), according to the government's new dietary
guidelines. Limit your intake of highly refined, low-fiber grain
products such as white bread. It's much better to get simple
carbs (sugars) from fruit, milk, and juice than from cake, cookies
(even if low-fat), or soda. There's nothing wrong with small
amounts of foods and beverages high in added sugar, but many
Americans eat too much of them, adding lots of calories, leaving
little room for more nutritious foods, and increasing the risk
of chronic disease.
The glycemic index
Various high-carbohydrate foods have different effects on blood
sugar. This effect is measured by the "glycemic index," which
is mentioned in many of today's diet books. The index indicates
how fast a food is digested into glucose and absorbed, and thus
how much it causes blood glucose to rise. Some studies suggest
that a diet rich in foods high on the glycemic index (meaning
they have a strong effect on blood sugar) increases the risk
of diabetes, at least in those pre-disposed to it, and lowers
HDL ("good") cholesterol.
The
index doesn't merely reflect whether the carbohydrates in a
food are simple or complex. Many factors come into play, including
the amount of fiber and fat in the food, how refined the ingredients
are, and whether the food was cooked. Table sugar and honey
are high on the glycemic index. But so are raisins, corn, potatoes,
carrots, watermelon, doughnuts, white bread, instant rice, and
most breakfast cereals. Apples, peaches, and ice cream, as well
as most beans, grapefruit, and peanuts, are low on the index.
Pasta is in the middle.
The
glycemic index has little practical use, however. You shouldn't
try to build your diet around it, as some well-known diet doctors
(including Dr. Atkins) advise. The main problem: it deals with
single foods eaten by themselves. Potatoes may be high on the
index, but when eaten as part of a meal, they have much less
of an effect on blood sugar. There is no reason to avoid foods
high on the glycemic index—many are very nutritious. Even
people predisposed to diabetes, or with the disease, can eat
these foods in moderation.
Sweet Nothings: Carb Myths
Myth:
Carbohydrates, especially sugars, are the leading cause of obesity.
Fact:
Eating more calories than you burn causes weight gain—it's
that simple. It doesn't matter where those calories come from,
as far as weight is concerned. Many obese people get into trouble
with excessive amounts of fat, not sugar or starch. In fact,
many "sweets" (cakes, ice cream, cookies) actually get most
of their calories from fat, not sugar. There's no evidence that
eating carbs stimulates appetite or leads to more or easier
fat storage and weight gain, as some carb-bashers claim.
Myth: Only refined sugar causes cavities.
Fact:
Refined sugar remains the leading dietary cause of tooth decay,
but sugars such as fructose in fruit and lactose in milk also
promote decay, as do some foods high in fermentable carbohydrates,
such as bread and rice. The most important factor: how sticky
the food is, since the longer the food remains on the teeth,
the more damage is done.
Myth: Sugar makes children hyperactive.
Fact:
Though for years parents have been blaming a high sugar intake
for their children's uncontrollable behavior, studies have found
no evidence for this.
Myth:
Sugar in fruit is good, sugar in candy is bad.
Fact:
The sugar in most fruit is primarily fructose, which has few,
if any, advantages over sucrose (the sugar in candy). So it
doesn't matter, for instance, if your jam is sweetened with
"sugar" or "fruit juice sweetener."
Myth: Honey and brown sugar are more healthful than table sugar
(sucrose).
Fact:
Neither offers significant nutritional advantages.
Source:
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