Article on good and bad carbs and the glycemic index - long

[Guest guest]

(AP) -- Should people really care that they digest potatoes faster

than carrots? Macaroni faster than spaghetti? Rice Krispies faster

than Special K? A greenish banana faster than a freckled one? A

Snickers bar faster than a Twix?

Yes, say some of the country's top-tier nutritional experts. They are

convinced that carbohydrates should be labeled good or bad, just the

way fats are, and that some of the carbs Americans love most --

velvety puddles of mashed potatoes, lighter-than-air white bread --

are dietary evil, to be avoided like the nastiest artery-choking

trans-fats.

No, contend other equally respected nutritional experts. Potatoes and

other starchy standbys are perfectly respectable. A carb is a carb is

a carb.

The debate involves an idea called the glycemic index. It is a way of

rating how quickly carbohydrates are digested and rush into the

bloodstream as sugar. Fast, in this case, is bad. In theory, a blast

of sugar makes insulin levels go up, and this, strangely, leaves

people quickly feeling hungry again.

The debate over whether every person who puts food in his mouth

should know about this is fervid even for the field of dietary

wisdom, where fierce opinions based on ironclad beliefs and sparse

data are standard.

Despite its detractors, the idea seems to be gaining momentum, in

part because it is offered as scientific underpinning by the authors

of a variety of popular diet schemes, mostly of the low-carb variety.

However, some painstakingly argue that the glycemic index is just as

important for the carbohydrate-loving brown rice aficionado as it is

for the most carbo-phobic, double-bacon-cheeseburger-hold-the-bun

Atkins follower.

To believers, the glycemic index is a kind of nutritional Rosetta

stone that explains much of what has gone wrong with the world's

health and girth over the past two decades: Why diets so often fail.

Why diabetes is becoming epidemic. Why mankind is growing so fat.

We overeat because we are hungry, the theory goes, and we are hungry

because of what we have been told to eat, which is too much fast-

burning food that plays havoc with metabolism by quickly raising

blood sugar levels. All of that starch at the base of the food

pyramid has had the unintended effect of making us ravenous.

" It's almost unethical to tell people to eat a low-fat, high-

carbohydrate

diet with no regard to glycemic index, " says Janette Brand- of

the University of Sydney, one of the field's pioneers.

Controversy weighs on subject

The idea has already entered the scientific mainstream in much of the

world and is endorsed by the World Health Organization, but it

remains deeply controversial in the United States. It is dismissed by

some of the country's weightiest private health societies, including

the American Heart Association and the American Diabetes Association.

To some of the skeptics, this is just another half-baked mishmash of

dietary arm-waving, cobbled together to justify the high-fat, low-

carb schemes that dietitians love to hate.

The fact that carbohydrates break down at different rates has been

suspected for a long time. It is why diabetics were once (but no

longer) told to studiously avoid sweets, since presumably sugary

foods would quickly turn into sugar in the blood stream. About 20

years ago, scientists came up with the glycemic index, or GI, as a

way to compare this.

The body converts all carbohydrates -- from starches to table sugar --

into sugar molecules that are burned or stored. The faster carbs are

broken down by the digestive system, the quicker blood sugar goes up

and the higher their GI.

The GI of at least 1,000 different foods has been measured, in the

process knocking down many common-sense dietary beliefs. For

instance, some complex carbohydrates are digested faster than the

long demonized simple carbs. Foods such

as white bread and some breakfast cereals break down in a flash,

while some sweet things, like apples and pears, take their time.

In general, starchy foods like refined grain products and potatoes

have a high GI -- 50 percent higher than table sugar. Unprocessed

grains, peas and beans have a moderate GI. Nonstarchy vegetables and

most fruits are low.

While it seems reasonable that chewy, whole-grain bread is digested

more slowly than a French baguette, some of the results are less

obvious. For instance, overcooking can raise the GI. Ripe fruit is

lower than green. A diced potato is lower than mashed, and thick

linguini is lower than thin.

To make matters even more confusing, the glycemic index measures only

the carbohydrate in food. Some vegetables, such as carrots, have

quite high GIs, but they don't contain much carb, so they have little

effect on blood sugar.

Therefore, some experts prefer to speak of food's glycemic load,

which is its glycemic index multiplied by the amount of carb in a

serving. Considered this way, a serving of carrots has a modest

glycemic load of 3, compared with 26 for an unadorned baked potato.

Metabolic havoc

Blood sugar levels may shoot twice as high after a high-GI meal as

after a low one, and that unleashes metabolic havoc: The body

responds with a surge of insulin, which prompts it to quickly store

the sugar in muscle and fat cells. The high sugar also inhibits

another hormone, glucagon, which ordinarily tells the body to burn

its stored fuel.

Blood sugar plunges. So much is stored so fast that within two or

three hours, levels may be lower than they were before the meal.

Suddenly, the body needs more fuel. But because glucagon is still in

short supply, the body does not tap into its fat supply for energy.

The inevitable result? Hunger.

That, at least, is the theory. Experiments to prove this are

difficult and time-consuming. Among those trying is Dr. Ludwig

of Boston's Children's Hospital, who has done several studies on

overweight teenagers.

In one, he tested the idea that a high-GI breakfast makes people

hungrier at lunch. A dozen obese boys were fed three different

breakfasts, all with the same calories -- a low-GI vegetable omelet

and fruit, medium-GI steel-cut oats or high-GI instant oatmeal.

At noon, they could eat as much as they wanted. Those who started the

day with instant oatmeal wolfed down nearly twice as much as those

getting the veggie omelet.

Ludwig says overweight people do not need to starve themselves. On a

low-GI diet, they can eat enough to feel satisfied and still lose

weight.

In a pilot study, he tested this on 14 overweight adolescents. They

were put on two different regimens -- a standard low-cal, low-fat,

high-carb diet and a low-GI plan that let them eat all they wanted.

After one year, the low-GI volunteers had dropped seven pounds of

pure fat. The others had put on four. Now he is repeating the study

on 100 heavy teenagers.

Even such small experiments have been rare. Most support for the idea

comes from big surveys that follow people's health and diets over

time. Some of these show that those who consistently favor low-GI

fare are less likely to become overweight or to get diabetes and

heart disease.

An artificial, confusing system?

The evidence is strong enough for authors of some popular diet books,

who use the glycemic index as one of their primary rationales. " It's

a new unifying concept that brings nutritional habits out of the dark

ages and says it's all about the numbers, " says Barry Sears, author

of the Zone series of diet books. " It says diet does not have to be

based on philosophy. It can be based on hard science. "

Major U.S. health organizations are less impressed. Ludwig expects

this to change, in part because paying attention to the glycemic

index can help everyone choose healthier carbs, whether they go low-

fat or high.

But that seems unlikely any time soon at the heart association. The

head of its nutrition committee, Dr. Eckel of the University

of Colorado, says the theory that high-GI foods make people hungry

is " ridiculous " and argues that a scientific case can be made for

just the opposite.

Dietitians generally encourage a balanced, varied diet emphasizing

unadulterated whole foods, and they cringe at a classification that

puts ordinary baked potatoes and white rice on a taboo list.

" It's an artificial system of classifying foods as good and bad, "

says JoAnn Carson, a nutritionist at the University of Texas

Southwestern Medical Center.

Others worry that the whole business is just too hard to keep

straight.

" We are putting before the public an extraordinarily complicated

message, which I don't think they will follow or be very happy with, "

says Dr. Xavier Pi-Sunyer of St. Luke's Roosevelt Hospital Center in

New York City.

Not necessarily, responds Harvard's Dr. Walter Willett. " I do think

this is an important concept for people to understand, but I don't

think they need to worry about specific numbers. "

His advice: Go light on the white bread, white rice, potatoes pasta

and sugary foods.

<A

HREF= " http://www.cnn.com/2003/HEALTH/diet.fitness/09/05/carb.confusion

..ap/index.html " >CNN.com - Good carb, bad carb? Experts debate labels -

Sep. 5, 2003</A>