Carbohydrates provide the most easily accessible energy source for your body. The other main sources of energy are protein and fats. During the digestive process, carbohydrates are broken down and absorbed in our circulatory system as sugars, called glucose.
As sugar levels rise, the pancreas releases insulin which allows the glucose to pass from the bloodstream to cells where they are used for energy. Diabetics either do not produce any insulin, do not produce enough insulin or produce insulin that does not work properly.
Studies have shown that certain types of carbohydrates accelerate the production of glucose while others delay that process. These studies have come up with an index, called the Glycemic index to measure the rate at which carbohydrates are converted into sugar in our bloodstream.
The glycemic index (GI) is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. In other words the glucose in the bloodstream increases rapidly. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health.
Follow this link for Foods with Glycemic Index, Fat and Carbohydrate Content data.
A food's glycemic index is determined by many factors, especially by how highly processed its carbohydrates are. The spiking of blood sugar levels is caused by highly processed carbohydrates, such as white flour and white rice, which have the outer bran and inner germ layer removed from the original kernel of grain. Whole-grain foods (like whole wheat flour and brown rice) have a lower glycemic index than their highly processed counterparts.
A high GI value is 70 or more. A medium GI is 56-69 and a low GI is 55 or less. Having a diet that is lower in GI is associated with better long term health.
Switching to eating mainly low GI carbohydrates that slowly trickle glucose into your blood stream keeps your energy levels balanced and means you will feel fuller for longer periods between meals. The basic technique for eating the low GI way is simply swapping high GI carbohydrates low GI carbohydrates. You don't need to count numbers or do any sort of mental arithmetic to make sure you are eating a healthy, low GI diet.
Before the discovery of the Glycemic Index, carbohydrates were identified as either simple or complex. Simple carbohydrates were believed to be absorbed quickly as sugars producing a rapid increase in blood sugar. Complex carbohydrates, like rice and potatoes were believed to be slowly digested and absorbed causing a slow rise in blood sugar levels. New research on how foods act in the body indicate that certain complex carbohydrates such as starchy foods like bread, potatoes and rice are digested and absorbed more quickly than had been assumed.
What Determines a Food's Glycemic Index?
Several factors affect the glycemic index of a food:
- Cooking method. Heat, amount of water and cooking time affect a food's GI. During cooking, water and heat expand the starch granules to varying degrees. Foods containing starch that has swollen (or gelatinized) to the bursting point, like boiled or baked potatoes, are more easily digested, and therefore, have higher GIs, than foods containing starch granules that are less gelatinized, like oatmeal, brown rice, and al dente spaghetti. For example, the GI of a baked potato is 85; brown rice is 50.
- Processing method. Grinding, rolling or milling starchy foods reduces particle size and makes it easier for water to be absorbed and digestive enzymes to attack the food. Processing can also remove the fibrous outer coat of the grain that slows down the access of digestive enzymes to the starch inside. Finely milled flours generally have a high GI. Coarse, stone-ground flours have larger-sized particles and lower GIs.
- Type of starch. The two types of starch in foods, amylose and amylopectin, have different effects on GI. Amylose molecules are harder to digest than amylopectin molecules. Legumes and basmati rice have a higher ratio of amylose to amylopectin, and therefore, have a lower GI than foods with more amylopectin. For example, the GI of basmati rice is 58; instant rice is 87.
- Fiber. The extent that fiber affects GI is unclear.(1). Some researchers believe that viscous, soluble fiber thickens the mixture of food in the digestive tract, which slows down enzymes from digesting the starch. This results in a lower blood sugar response, and a lower GI. Legumes and oats contain soluble fiber and have low GIs.
- Sugar. GI is affected by the type of sugar in a food. Sucrose (table sugar), which is made up of glucose and fructose, has a lower GI than glucose because half of the sucrose molecule is made up of fructose, a type of sugar that elicits a very small blood sugar response. For example, the GI of sucrose is 68; the GI of glucose is 100. It would seem that adding sugar to a meal should lower the GI, but, surprisingly, a few studies have not found this to be so.
- Fat. Fat increases the time it takes for food to leave the stomach and enter the intestine. By slowing the rate that carbohydrates are digested in the intestine, fat-containing foods may temper the rise in blood sugar and yield a lower GI than similar foods without fat. For example, the GI of potato chips is 57, French fries is 75 and baked potato is 85. However, that does not make potato chips a better choice than the more nutritious baked potato.
- Acidity. Acid in food slows down stomach emptying, which slows the rate that carbohydrates are digested. Increasing the acidity in a meal can lower its GI and the blood sugar response. Vinegar, lemon juice and sourdough bread provide this benefit.
A mixed meal alters the glycemic index of a food. When a particular food is eaten along with other foods, the blood glucose response and glycemic index will vary, depending on the proportion of carbohydrate, protein, and fat in the mixed meal. Adding protein to a meal containing carbohydrate increases the insulin response to the meal, but blood sugar does not change much or actually decreases. Adding fat to a carbohydrate meal increases insulin secretion but decreases blood sugar response. Studies have shown that fat and protein affect the actual glycemic response of a meal.
Some GI diet books may leave consumers thinking that some carbohydrates are good and some are bad, but the bad ones—the ones with a high GI—should be avoided. This is also not advisable since people who restrict their diets to low GI foods may miss out on the nutritional and health benefits of wholesome foods, like those vegetables, fruits and whole grain foods that happen to have higher GI values. Since these foods tend to be rich in vitamins, minerals, fiber and phytochemicals, they are considered good food choices, no matter where they fall on the GI scale. On the other hand, foods that are high in fat, like potato chips or chocolate covered peanuts, should be eaten sparingly, even though they have a low GI.
Although the glycemic index has the potential to be a valuable clinical tool, more research, including long-term clinical studies, are needed to prove its worth in preventing disease. For now, consumers should focus on eating a mostly plant-based diet that includes a wide variety of vegetables, fruits, whole grains and legumes. There is much evidence that a mostly plant-based diet can reduce the risk of diseases, like cancer, heart diseases and diabetes. In most cases, such a diet will have a low glycemic index. Whether a low GI diet is the preventive agent in reducing disease or is simply a marker for a varied, healthful diet is yet to be determined.
Additional research indicated that moderate amounts of sugar did not produce dramatic rises in blood sugar as had been thought.
The official home for the glycemic index and international GI database is in the Human Nutrition Unit, School of Molecular and Microbial Biosciences, University of Sydney. It's website is: www.glycemicindex.com.
The American Diabetes Association recognizes that some studies have shown small improvements in glucose levels of people who follow a diet based on the glycemic index. However, the American Diabetes Association does not recommend strict adherence to a diet based on the glycemic index. Instead, they recommend adjusting your diet and/or your medication.
Follow this link for Foods with Glycemic Index, Fat and Carbohydrate Content data.