The glycemic index compares the potential of foods containing the same amount of carbohydrate to raise blood glucose. The theory behind the Glycemic Index is simply to minimize insulin-related problems by identifying and avoiding foods that have the greatest effect on your blood sugar
To determine the glycemic index of a food, volunteers are typically given a test food that provides 50 grams of carbohydrate and a control food (white bread or pure glucose) that provides the same amount of carbohydrate on different days. Blood samples for the determination of glucose levels in calculation of glycemic index are taken prior to eating (fasting blood sugar or pre-prandial) and at regular intervals after eating (post-prandial) over the next several hours. The results for changes in blood glucose levels over time are plotted as a curve and summarized as glucose AUC, or "area under the curve."
However, the amount of carbohydrate consumed also affects blood glucose levels and insulin responses.
The glycemic index of a food is defined as the incremental area under the two-hour blood glucose response curve (AUC) following a 12-hour fast and ingestion of a food with a certain quantity of available carbohydrate (usually 50 g).
The glycemic index is calculated plotting the area under the glucose curve after the test food (carbohydrate 50g) is eaten, divided by the corresponding area after the control food is eaten. The Area under the Curve of the test food is divided by the Ares Under Curve of the standard (either glucose or white bread), and multiplied by 100 to represent a percentage of the control food.
Pure glucose serves as a control, and is given a Glycemic Index (GI) of 100. Glycemic Index uses a scale of 0 to 100, with higher values given to foods that cause the most rapid rise in blood sugar.
The average Glycemic Index value is calculated from clinical data collected in 10 human subjects. Both the standard and test food must contain an equal amount of available carbohydrate. The result provides a relative ranking of Glycemic Index value for each tested food.
Some other factors that can affect a food’s glycemic index include the following:
• The different botanical variety of the food, have different glycemic index values.
• Glycemic Index depends upon the processing of the food.
• Glycemic Index depends upon how a food is prepared.
• Acidity. Acidic foods tend to have a lower glycemic index than similar, less-acidic foods.
• Presence of sucrose. Presence of sucrose in food lowers the Glycemic Index. Table sugar (sucrose) is half glucose, which has a high glycemic index, and half fructose, which has a low glycemic index.
• Fiber. Some types of fiber lower a food’s glycemic index. Insoluble fiber, the type found in wheat, has little effect on glycemic index. Soluble fiber, on the other hand, lowers glycemic index.
Glycemic Index values are generally divided into three categories:
Low GI: (1 to 55) beets, chickpeas, fructose, intact grains, legumes/pulses, nuts, kidney beans, sugar-sweetened beverages, tomatoes, white rice, white bread, pretzels, white bagels, white baked potatoes.
Medium GI: (56 to 69) bananas, baked potatoes, basmati rice, corn on the cob (corn-stick or long maize), grapes, ice cream, raisins, spaghetti, sucrose, sweet potato, whole wheat products.
High GI: (70 and higher) carrots, corn flakes, extruded breakfast cereals, glucose, hummus, kidney beans, maltose, maltodextrins, oatmeal, peanuts, peas, skim milk, white bread, most white rices.
A more accurate indicator of the relative glycemic response to dietary carbohydrates should be glycemic load, which includes the relative quality and quantity of carbohydrates in the diet. The concept of glycemic load was developed by scientists to simultaneously describe the quality (glycemic index) and quantity of carbohydrate in a meal or diet.
The glycemic load of a food is calculated by multiplying the glycemic index by the amount of carbohydrate in grams provided by a food and dividing the total by 100.
Glycemic load = (glycemic index × grams of carbohydrate) ÷ 100.
Glycemic Load Improves the Glycemic Index because your body's glycemic response is dependent on both the type and the amount of carbohydrate consumed. Therefore, you can control your glycemic response by consuming low-GI foods and/or by restricting your intake of carbohydrates.
Some strategies for lowering dietary glycemic load include:
• Increasing the consumption of fruits, legumes, nuts, whole grains and no starchy vegetables in your diet.
• Decreasing the consumption of starchy high-glycemic index foods like potatoes, white rice, and white bread in your diet.
• Decreasing the consumption of sugary foods like cakes, candy, cookies and soft-drinks in your diet.
Physiological Responses to High- Glycemic Index v/s Low-Glycemic Index Foods
i). The consumption of high-glycemic index foods leads to higher and more rapid increases in blood glucose levels than the consumption of low-glycemic index foods.
ii). Rapid increases in blood glucose are potent signals to the beta-cells of the pancreas to increase insulin secretion.
iii). subsequently, the high insulin levels induced by consumption of high-glycemic index foods may cause a sharp decrease in blood glucose levels (hypoglycemia).
iv). The consumption of low-glycemic index foods results in lower but more sustained increases in blood glucose and lower insulin demands on pancreatic beta-cells.
v). A low-GI food will release glucose more slowly and steadily, which leads to more suitable postprandial (after meal) blood glucose readings. A high-GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after exercise or for a person experiencing hypoglycemia (lesser glucose levels in blood).
Benefits of Glycemic Load
After a high-glycemic load meal, blood glucose levels rise more rapidly and insulin demand is greater than after a low-glycemic load meal.
Role of Glycemic Index foods
- Low-glycemic-index diets may be especially effective in helping persons reduce waist circumference, body fat, and body weight. There is a little scientific evidence supporting the role of the GI diet in weight loss.
- Consumption of low-glycemic index foods delays the return of hunger, decreased subsequent food intake, and increased satiety (feeling full) when compared to high-glycemic index foods.
- In addition to weight loss, a low-glycemic diet has been connected to better blood sugar and insulin control, disease prevention, increased energy, and improved mood.
- High dietary glycemic loads are also associated with increased serum triglyceride concentrations and decreased HDL cholesterol concentrations; decreasing the risk factors for cardiovascular disease.
- Clinical research finding associates high-glycemic-index and/or high-glycemic-load diets with cancer (breast, ovarian, endometrial, and colorectal), coronary heart disease and heart attacks, degeneration, high cholesterol and triglycerides, and high C-reactive protein.
- Similarly, low-GI diets have been associated with age-related macular degeneration (AMD), chronic kidney disease, decreased risk of cancers of breast, colon, pancreas, prostate; depression, formation of gall stones, formation of uterine fibroids, metabolic syndrome, neural tube defects, type 2 diabetes, stroke.
- Clinical finding have shown that individuals who followed a low-Glycemic Index diet were at a significantly lower risk for developing both type 2 diabetes, coronary heart disease. High blood glucose levels or repeated glycemic "spikes" following a meal, may promote above mentioned diseases by increasing systemic glycative stress (causing lesion), other oxidative stress (imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to repair the resulting damage) to the vasculature (the arrangement of blood vessels within an organ) and also by the direct increase in insulin levels.
Glycemic index diet
The term "glycemic index diet" usually refers to a specific diet plan that uses the glycemic index as the primary or only guide for meal planning. The purpose of a glycemic index (GI) diet is to eat carbohydrate-containing foods that are less likely to cause large increases in blood sugar levels.
The diet is a means to lose weight and prevent chronic diseases related to obesity such as diabetes and cardiovascular disease.
You might choose to follow the GI diet because you:
- Want to lose weight or maintain a healthy weight.
- Need help planning and eating healthier meals.
- Need help maintaining blood sugar levels as part of a diabetes treatment plan.
Limitations of glycemic index:
- The GI value of any food item is affected by several factors, including how the food is prepared, how it is processed and what other foods are eaten at the same time. Glycemic index charts often give only one value per food, but variations are possible due to variety, ripeness (riper fruits contain more sugars increasing GI), cooking methods (the more cooked, or over cooked, a food the more its cellular structure is broken with a tendency for it to digest quickly and raise GI more), processing (e.g., flour has a higher Glycemic Index than the whole grain) and the length of storage.
- One limitation of Glycemic Index values is that Glycemic Index values do not reflect the likely quantity you would eat of a particular food.
- Therefore glycemic index works better at constant sugar levels. When you eat foods that cause a large and rapid glycemic response, you may feel an initial elevation in energy and mood as your blood sugar rises, but this is followed by a cycle of increased fat storage, lethargy, and more hunger.
- A glycemic index diet doesn't necessarily specify portion sizes or the optimal number of calories, carbohydrates, or fats for weight loss or weight maintenance.
- A lower glycemic response usually equates to a lower insulin demand but not always, and may improve long-term blood glucose control and blood lipids.
- It's important to remember that the Glycemic Index is only a rating of a food's carbohydrate content. If you use Glycemic Index and Glycemic Load values as the sole factor for determining your diet, you can easily end up over consuming fat and total Calories.
Limitations of glycemic load
- Glycemic load (GL) is more of a qualitative than quantitative measurement.