The Glycaemic Index (GI) is a numerical scale used to indicate how fast and how high a particular food can raise our blood glucose (blood sugar) level. A food with a low GI will typically prompt a moderate rise in blood glucose, while a food with a high GI may cause our blood glucose level to increase above the optimal level.
An awareness of foods' Glycaemic Index can help you control your blood sugar levels, and by doing so, may help you prevent heart disease, improve cholesterol levels, prevent insulin resistance and type-2 diabetes, prevent certain cancers, and achieve or maintain a healthy weight. A substantial amount of research suggests a low GI diet provides these significant health benefits. So, it's worth taking a look at the basic principles of a low GI way of eating.
High carbohydrate foods, even wholesome foods that are high in carbohydrates such as satisfying whole grain breads, delicious fruits, starchy vegetables, and legumes, can have an affect on blood glucose.
Carbohydrate-rich foods include:
• Starches, which are found in foods such as
o Grains (foods made from wheat, barley, rice, etc.)
o Legumes, (split peas, lentils and dry beans such as pinto, kidney, black, etc.)
o Starchy vegetables (potatoes, winter squash, yams, etc.)
• Sugars, such as those naturally found in fruits and dairy products as well as packaged sweeteners, and sugars added in processing.
• Fiber—the indigestible portion of carbohydrates. However, even though fiber is considered a carbohydrate, since it is not digested (except sometimes very late in the digestive process by bacteria in the large intestine), does not directly raise blood glucose levels.
After we eat carbohydrate-rich foods, our digestive process usually breaks them down, and eventually turns them into glucose, which can then enter our bloodstream. (Since most proteins and fats from food are not turned into glucose by this same process, they typically have much less of an immediate effect on our blood sugar).
The presence of glucose in the bloodstream usually triggers the production of insulin, a hormone that helps glucose get into cells where it can be used for energy. Once our immediate energy needs have been met, extra glucose still remaining in the bloodstream can be stored in our muscles and liver for later use. If our muscle and liver stores of glucose are full, but we still have extra glucose floating around in our blood, then insulin can help our body store this excess sugar as fat.
Since insulin helps glucose get into cells where energy is made, insulin is vital to fueling the body. However, too much insulin secretion over long periods of time can cause problems. Research shows that prolonged exposure to elevated levels of insulin can cause:
• high triglycerides
• high “bad” LDL cholesterol
• low “good” HDL cholesterol
• high blood pressure
• insulin resistance
• increased appetite
• risk of developing or exacerbating type 2 diabetes
When a certain combination of these disease-promoting factors is present all at once, the constellation of symptoms is called Metabolic Syndrome. The presence of these symptoms also raises a person's risk of cardiovascular disease, diabetes, and prostate or breast cancer. In studies reported in the American Journal of Clinical Nutrition in 2002, diets high in carbohydrates that had a high GI were linked to a greater risk of coronary heart disease. Several prospective observational studies have shown that the continual eating of foods with a high GI is linked to an increased risk of developing chronic conditions such as cardiovascular disease, type 2 diabetes and certain cancers. In a recent study that evaluated more than 65,000 American women, a high dietary GI was positively associated with an increased risk for type 2 diabetes.
An article appearing in the October 2003 issue of Critical Reviews in Food Science and Nutrition by Drs. Stacey Bell and Barry Sears explains in detail what happens metabolically when a high glycaemic load meal or snack is eaten. (The glycemic load represents the food's glycaemic index multiplied by the quantity of the food consumed by weight.)In their study of healthy volunteers, Bell and Sears found that two hours after eating a high glycaemic load meal, blood sugar levels were twice as high as the levels that resulted from consumption of a low glycaemic load meal. These high blood sugar levels triggered the synthesis and release of insulin, our key hormone for getting sugar back out of the bloodstream and into the cells.
While a single, high-GI meal might not cause significant health problems for our body, frequent consumption of high glycaemic load meals can result in perpetually high insulin levels. When insulin levels stay high, our endocrine system can start out on a rollercoaster ride in which the body tries to adjust to its perpetually high insulin level with changes in other hormone levels that can leave us both tired, hungry, and on a course toward increased risk of cardiovascular disease and type 2 diabetes.
By contrast, many or all of these unfavorable hormonal shifts become less likely when a meal with low glycaemic load is eaten. Since low glycaemic meals take longer to digest and absorb, and nutrients are released gradually, blood sugar levels tend to remain more stable and insulin levels tend to rise in a non-risky fashion. As an added benefit, a low glycaemic way of eating is associated with lower levels of LDL-cholesterol and triglycerides. Bell and Sears suggest that an optimal glycaemic load diet would keep the glycaemic load under 50 and be made up of 40% low glycaemic index/glycaemic load carbohydrates, 30% low-fat protein, and 30% fat.
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