Entries Tagged 'Glycemic Diet' ↓

Gelatinization – The more starch granules are swollen and burst during cooking the higher the GI. For this reason baked potatoes have a high glycemic index (85) whereas pasta is unique in that the internal starch granules are entrapped and not as swollen leading to lower glycemic values (30-60). Pasta cooked al dente (slightly uncooked core) has an even lower glycemic value because of this.

Amylose to Amylopectin ratio - The Amylose to amylopectin ratio similarly determines a food’s glycemic index by the amount of gelatinization that occurs. Foods with higher amylase (which less readily gelatinize and digest) have lower glycemic values than foods with higher amylopectin (which more readily gelatinize and digest). For example basmati rice with higher amounts of amylase, has a lower glycemic value (58). Conversely, Japanese style white rice with lower amounts of amylase, has a higher glycemic value (83).

Processing - Grinding wheat into smaller particles increasing the surface area for digestive enzymes. The more finely milled the higher the glycemic index. In this example the degree of processing determines the relative glycemic index of wheat (whole wheat < cracked wheat < course four < white flour).

Fiber – This depends on whether the fiber acts as a protective barrier or not. For instance most wheat bread (73) has the same glycemic index as white bread (70) because the fiber is not intact and does not play a protective role. When fiber plays a protective role to digestive processes such as is the case with stone ground (cracked kernel) wheat bread the glycemic value is lower (53).

Dr. David Jenkins at the University of Toronto developed the glycemic index to more accurately describe how different carbohydrates affect blood sugar levels.  The higher the glycemic index value the more easily a given carbohydrate is metabolized into glucose and the greater the resulting insulin response.

White bread or glucose is used as the reference food where the glycemic index for each is set at 100.  It’s important to know which reference is used when comparing glycemic index numbers because the white bread based glycemic index value will be higher for a given carbohydrate than the glucose based glycemic index.  To convert the white bread based glycemic index reference value to the glucose based glycemic index reference you multiply by 0.7 (the glycemic index of white bread is 70 on the glucose reference based standard).  To avoid any confusion I will only use the glucose reference standard.¹

High glycemic foods (65 and above) include things you would expect like jelly beans (78) but also items you may not expect such as baked potatoes (85) and white bread (70).  In this example “complex” carbohydrates such as potatoes can have a greater impact on blood sugar than “simple” sugars such as found in jelly beans.

Carbohydrates are found in sugar, bread, cereals, fruits and vegetables.  All carbohydrates, with the exception of fiber which is indigestible, are broken down into sugar and the resulting increase of glucose in the bloodstream causes insulin to be released.  Insulin shuttles the glucose to muscle and liver cells resulting in a lowering of blood sugar.

Refined carbohydrates, found in refined flours and sugars, are more easily digested by the body leading to higher levels of blood glucose and a greater insulin response than less processed carbohydrates such as whole grains, beans, fruits and most vegetables.  This heightened insulin response to refined carbohydrates leads to a more rapid decline in blood glucose from peak levels and causes a more rapid return of hunger.

High glycemic index diets, from refined carbohydrates, increases the risk of coronary heart disease by 1.98 times compared with low GI diets.¹  Furthermore carbohydrates classified by glycemic index were found to be a stronger predictor of coronary heart disease than the traditional classification of “simple” and “complex”.  This again suggests that the glycemic index is a more accurate measure of a carbohydrate’s effect on our blood chemistry and resulting health.

1.                  A prospective study of dietary glycemic load, carbohydrate intake and risk of coronary heart disease in women. Am J Clin Nutr 2000;71:1455-61

Results of the Nurses’ Health Study, a longitudinal study of diet and lifestyle factors among 65,000 Nurses followed since 1986, suggest that diets with a high insulin demand (high glycemic index) lead to an increased risk of diabetes.¹

In this study, Dr. Walter Willet at the Harvard school of Public Health, found that high glycemic diets (which included cola beverages, white bread, white rice, French fried potatoes, and cook potatoes) increased the risk of developing diabetes by 1.47 times compared with low glycemic diets.  Furthermore when dietary fiber was factored in, diets with a high glycemic index and low cereal fiber increased the risk by 2.5 times.

Another study of 43 thousand Finish men and women found a 35% risk reduction of developing diabetes in participants with high whole grain intake compared to participants with low whole grain intake.² Although not measured directly, this suggests that a low GI diet represented by a high whole grain intake reduces the risk of diabetes mellitus.

1.                  Dietary Fiber, Glycemic Load, and Risk of Non-insulin-dependent Diabetes Mellitus in Women.  1997 JAMA; 277:472-477

2.        Whole-grain and fiber intake and the incidence of type 2 diabetes.  2003 Am J Clin Nutr;77:622-9