For over a hundred years, people with diabetes have been given advice on what to eat Many diets were based more on unproven (although seemingly logical) theories, rather than actual research. In 1915, for example, the Boston Medical and Surgical Journal advocated that the best dietary treatment for someone with diabetes was ‘limitation of all components of the diet’. This translated into a very low kilojoule diet interspersed with days of fasting. Unfortunately, malnutrition was often the result!

In the 1920s doctors began recommending high fat diets for their patients. Ignorant of the dangers of a high fat diet, they knew that fat, at least, didn’t break down to become blood sugar.

It was not until the 1970s that carbohydrate was considered to be a valuable part of the diabetic diet Researchers found that not only did the nutritional status of patients improve with a higher carbohydrate intake, but their blood sugar levels improved as well.

The only part of food which directly affects blood sugar levels is carbohydrate. When we eat carbohydrate foods, they are broken down into sugar and cause the blood sugar levels to rise. The body responds by releasing insulin into the blood. The insulin clears the sugar from the blood, moving it into the muscles where it is used for energy, so the blood sugar level returns to normal.

Some people think that because carbohydrate raises the blood sugar level, it should not be eaten at all by people who have diabetes. This is not correct. Carbohydrate is a normal part of the diet and at least half of our total daily kilojoules should come from carbohydrate. In fact, the more carbohydrate you eat the better because it automatically reduces the proportion of kilojoules you get from fat.

The secret to the diabetic diet is not so much the quantity but the type of carbohydrate.

Traditionally sugar was excluded from diabetic diets because it was thought to be the worst type of carbohydrate. The simple structure of sugar supposedly made it more rapidly digested and absorbed than other types of carbohydrate, like starch. This assumption was simply not correct. Even in the late 1970s, test meal studies showed that there was a great deal of overlap between the blood sugar responses to sugary and starchy foods. Fifty grams of carbohydrate eaten as potato caused a similar rise in blood sugar as 50 grams of sugar. Ice cream resulted in a lower blood sugar response than potato! Findings like these sparked research into the G.I. factor in an effort to learn more about how the body actually responds to different carbohydrate foods.

The emphasis through the 1970s and for much of the 1980s, was on the quantity of carbohydrate in the diet. ‘Portion’ diets were used to prescribe a set amount of carbohydrate to be eaten at every meal. (A carbohydrate portion* is an amount of carbohydrate-rich food which contains 10 to 15 grams of carbohydrate—depending on which country, or State of Australia—you lived in. So, not only was the portion system complicated, portion sizes varied throughout the world!).

An underlying assumption of the carbohydrate portions theory, was that equivalent amounts of carbohydrate, irrespective of the type, cause an equal change in the blood sugar level. This reasoning had no scientific backing and has since clearly been shown to be incorrect. Fortunately, good quality scientific research supports today’s dietary recommendations for people with diabetes. While the G.I. factor research has not negated the significance of the quantity of carbohydrate in the diet, it has shown us the importance of considering the type of carbohydrate food that we include.

The G.I. factor has shown us that the way to increase the quantity of carbohydrate in the diabetic diet, without increasing the sugar levels in the blood, is to choose carbohydrate foods with a low G.I. factor.

Our research has shown that blood sugar levels in people with diabetes are greatly improved if foods with a low G.I. factor are substituted for high G.I. factor foods.

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