GI/GL: Wheres The Value?

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Good, bad carb definitions misleading, says review

By Lorraine Heller

01/10/2007 - Dividing carbohydrates into 'good' and

'bad' carbs is misleading, and cannot be used as a

measurement to prevent overweight and obesity,

according to a review of scientific literature on the

contentious topic.

Conducted by University of Virginia professor Glenn

Gaesser and published in this month's issue of the

Journal of the American Dietetic Association, the

review analyzes peer-reviewed research on carbohydrate

consumption, glycemic index and body weight.

It claims to be the first detailed review of

literature on the link between carbohydrate

consumption and body weight, with its findings running

counter to the current consensus on the effects of

'good' and 'bad' carbohydrates.

According to Gaesser, diets high in carbohydrates are

almost universally associated with slimmer bodies.

Additionally, his review found that consuming high

levels of high-glycemic foods is not associated with

higher body weights. On the contrary, he said, several

large studies in the United States revealed that

high-glycemic diets were linked to better weight

control.

" There is no reason to be eating fewer carbs - they're

not the enemy, " he said.

The description of carbohydrates as 'good' or 'bad' is

based on glycemic index (GI), a measure of the quality

of the carbohydrate in terms of how much it raises

blood sugar.

The glycemic index measures how quickly certain foods

release carbohydrates into the body, which then raise

consumers' blood glucose levels. High GI foods,

including white bread, white rice, many prepared

breakfast cereals and concentrated sugar, are

considered by many as 'bad' carbs, as they cause blood

sugar levels to rise more rapidly. Low GI foods

include most vegetables, fruits, beans and unprocessed

grains, and are considered 'good' carbs.

As science emerges showing that low-GI foods can help

control weight and more certainly, help reduce the

risk of diabetes and related conditions, a wider

cross-section of consumers is selecting foods based on

the GI index.

However, a major obstacle when it comes to using GI as

a measure of a product's health benefits is that this

is not consistent. Scientific literature remains mixed

and insufficient, and results in fuelling confusion

rather than providing reliable guidance.

Indeed, according to a group of industry and science

experts, the glycemic index equation is not quite as

simple as " low GI= good and high GI= bad. " For

example, chocolate cake has what is considered a low

GI, while some whole grain cereals can have a medium

to high GI.

In the US, the Glycemic (Net) Carbohydrate Definition

Committee of the American Association of Cereal

Chemists (AACC) International, last year approved a

new set of definitions related to glycemic

carbohydrates in an effort to find a compromise on a

complex and inconsistent issue.

The Committee settled on four definitions designed to

" provide a measurable definition that will enable

manufacturers to communicate the glycemic response in

grams per serving of food. " These were: 'available

carbohydrate', 'glycemic response', glycemic

carbohydrate', and 'glycemic impact'.

According to Gaesser's recent review, GI itself is not

a reliable description of carbohydrate quality,

despite its use by a number of popular low-carb diets.

" Digestion is a complicated process. It's very

difficult to determine the GI of a whole meal, for

instance, so it doesn't really make sense to use GI or

'glycemic load' - the glycemic index multiplied by the

quantity ingested - as a guide to eating. "

Following his review of " hundreds " of articles on

large-scale studies using surveys or randomized,

controlled trials, Gaesser said they show that " people

who consume high-carb diets tend to be slimmer, and

often healthier, than people who consume low-carb

diets. "

" Even high-glycemic foods have a place in the diet,

attributing that to the overall higher quality of a

high-carb diet, which includes more fiber-rich and

other nutritional foods. "

The general consensus of the scientific community is

that more science is necessary to determine the health

outcomes of the glycemic index, and until that is

available it urges caution in the use of GI labels and

claims.

In an attempt to better understand the glycaemic

index, researchers from the Mayer USDA Human

Nutrition Research Center on Aging at Tufts University

(USDA HNRCA) recently used a simple test food, white

bread, to show that a relatively high level of

inter-individual (among different individuals), and

intra-individual (within the same individual)

variability occurs on consumption of white bread.

They found that individual variations in the glycaemic

index (GI) of white bread, stated as 70 in the

literature, may range from 44 to 132, which again

highlights the complexity of the GI system of

measurement.

Jeff Novick, MS, RD, LD/N

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