HEALTH & FITNESS

By Martin Schultz

And we dutifully followed the party line. Bread disappeared from dinner tables, spaghetti Bolognese from restaurant menus.

Fast forward to 2006. The carbohydrate debate has been transformed. The Atkins fanaticism has given way to a more realistic understanding of the nature and function of carbohydrates. Today, diet researchers tend to stratify carbohydrates according to whether they provide, on balance, more healthful nutritional assistance or a mainly glucose punch. Yet there are no entirely good or entirely bad carbohydrates. Some support wellness, others can raise the risk factors for coronary disease and diabetes.

When the body digests carbohydrates, they enter the bloodstream in the form of sugars. Each individual food ingredient has a specific rate at which its carbohydrates (sugars) pass into the bloodstream and cause blood sugar levels to rise.

Canadian researchers created a system for classifying carbohydrates based on their impact on blood-sugar rates. They were looking for a kind of job aid for diabetics – a blood sugar quick reference guide. This system became known as the glycemic index (GI). Professor Jennie-Brand Miller, of the University of Sydney in Australia expanded the glycemic index to cover some 750 food products. New food products are constantly being added.

Many people rely on the glycemic index: dieters who follow its food rankings, athletes who need to know which foods will boost their energy levels, and food manufacturers who produce food items with labels proclaiming their GI status. But all is not perfect in GI land.

The index disguises subtleties, disagreements among researchers, even contradictions of rankings that belie its apparent usefulness.

Sweet Ranking
GI is a system of rankings based on a scale of 0 to 100 depending on how quickly a carbohydrate is transformed into glucose. For reference purposes, pure glucose is given a GI ranking of 100. The higher the food’s ranking, the faster the blood sugar passes into the bloodstream.

For example, popcorn converts almost instantly to blood sugar and therefore has a high GI rating. Rye bread, conversely, affects blood sugar levels much more gradually and consequently has a low GI.

Typically, foods with a GI rating below 55 are thought to be “better for you” than those exceeding 55. Often low-GI foods are healthier choices altogether because they typically also possess a high fiber content and are likely to be low in fat as well as calories and cholesterol. While many food components are easily identified as having a high GI, others are more likely to shock an observer. Thus, a potato cooked in its skin has a rating of 85 due to its high starch content. Perhaps more surprising still is that parsnips have a GI as high as 97.

There is also the issue of how much processing a food requires. When a grain’s bran, which contains the highest fiber in the food, is stripped away, it leaves the starchy interior of the carbohydrate. Without its outer hull, the grain’s carbohydrate content rapidly enters the bloodstream.
Other factors influence blood-glucose levels. For example, finely ground grains have a higher GI rating than coarser types of grain. Also, the freshness of the food can affect its breakdown into glucose.
GI’s purpose is purely qualitative in reality: solely measuring how quickly carbohydrates increase blood glucose. Another argument suggests it is just as critical to consider the quantity of glucose produced and its impact on the body’s ability to produce insulin. This contention induced Harvard University scientists to advance the concept of the glycemic load (GL), a formula that calculates the quantity of carbohydrates in a meal serving.

Looked at together, GI and GL reveal a connection between high blood-glucose levels and large insulin demands, which can be a cause of diabetes. Among the foods most typically connected with diabetes are white bread, sugar-sweetened drinks, and potatoes — three items with an elevated GI ranking.
By contrast, a low-GL diet is normally identified with better diabetes management. As many nutritionists and cardiologists suggest, using GI to maintain healthy glucose levels and minimize insulin resistance has a strong effect on both heart disease and obesity issues. In reality, low-GI, high-fiber diets help to reduce obesity by extending the feeling of being full.

Challenging the Index
Controversial for the 26 years of its existence, GI does have restrictions. For example, critics note that the 750 food components so far tested represent only a small fraction of total common foods and more food items appear all the time. They also charge that there’s
no general consensus on GI ratings. No one accepts any one list, so the same food item can have several different ratings depending on how its blood glucose level is measured.

Many criticize the index for its simplicity. The result is confusion. Some people believe GI is too simple, others that it is too complicated. Many no longer use it as a guide. Instead, they’ve converted the index into just another diet aid, even using it to support other diet practices, such as low-carb diets that exist only by morphing into low-GI diets.

Some would say that we’re all searching for a comfortable way to diet, when we should be following the more sensible though less convenient federal dietary guidelines. The glycemic index should ultimately be recognized for what it is, a food-management tool.

Such tools can help us make more informed dieting decisions, but they cannot replace common sense. •