What Is The Glycemic Index?
The glycemic index tells us how fast a carbohydrate food is absorbed. It rates foods based on how quickly it causes blood glucose to rise and fall, which affects energy levels. Foods are scored from 0-100, commonly within the range of 50-100. A Higher glycemic score causes a greater rise in blood glucose. This is a useful tool in determining which foods may be causing fluctuations in energy.
High glycemic foods cause a greater Insulin release to deal with high glucose levels in the blood. Insulin stores a large Proportion of glucose in muscles, the liver, and fat cells. High amounts of insulin cause blood glucose to decline rapidly. Following the rapid absorption of glucose, feelings of hunger and low energy can occur. Foods high in simple sugars promote a high glycemic response.
How Does The Glycemic Score Relate To Energy?
A lower glycemic score will induce a steady state insulin response. Insulin is released slowly and allocates the glucose to cells. This makes blood glucose levels more stable, declining slower. This enables sustained energy and stable appetite.
A higher glycemic score does not mean that more glucose is stored as fat. The clearing of blood glucose Is quicker, so we are hungrier sooner and will eat sooner and more often. We therefore consume more calories that weren’t needed. This is one factor in appetite regulation but not the determining variable.
Refined carbohydrates and sugary foods, although delicious and satisfying will nutritionally double cross you. You may experience blood glucose fluctuations, disrupted appetite and craving to eat more.
The GI should not be the defining guideline in deciding what you include in your diet. It is useful as a supplementary tool to identify foods and their energy efficiency. The goal is to promote steady rises and falls in blood glucose, keeping an eye on high GI foods and portion sizes.
Apply common sense. Natural foods such as potatoes may have a high GI but also contain fibre and are rich in nutrients. No harm done provided the Glycemic load (serving size) isn’t too large. Consuming things like doughnuts will spike blood sugar with no nutritional value. At least with foods like fruits and potatoes you’ve got some nutrients.
GI relates to rate of carbohydrate digestion and compares equal portions of carbohydrates:
Measures – 25g sugar/25g pasta (quality) and not overall quantity.
Glycemic load refers to the quantity of carbohydrate. GL can be viewed as a portion size. GL determines the total amount of carbohydrate and it’s GI. The higher the GL the higher the expected elevation in blood glucose.
There is a correlation between high Glycemic load and diabetes, and CVD (1,2). Low GI foods promote protective effects against the development of diabetes and cardiovascular disease (3). Although evidence suggests protective effects of low GI foods, the presence of fibre and antioxidants are also preventative in the development of CVD, diabetes, obesity and cancer (4,5). Ideally a low GI, GL is what to go for, however fibre and antioxidants are also present in high GI foods such as bananas and potatoes. These are the exceptions amongst similar plant based foods. It is the high GI, low nutrient foods that should be avoided such as sugar and refined grains. You can consult the glycemic index of foods to ensure a well balanced mix.
Calculate GI & GL
GL = GI * amount of available carbohydrate/100
GI = GL/100 * amount of available carbohydrate
A banana weighs 255g of which 45.5g is carbohydrate. It has a GI of 52.
52 * 45.5/100 = 24
Foods with a GL under 10 raise blood glucose the least
20 and above cause spikes in blood sugar and subsequently insulin
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- Liu S, Willett W, Stampfer M, Hu F, Franz M, Sampson L, Hennekens C, Manson C. 2000. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. The American Journal of Clinical Nutrition. 71:1455–61.
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- Rimm EB, Ascherio A, Giovannucci E, Spiegelman D, Stampfer MJ, Willett WC. 1996. Vegetable, fruit and cereal fiber intake and risk of coronary heart disease among men. The Journal of the American Medical Association. 275:447– 451.
- Slavina. J. 2003. Why whole grains are protective: biological mechanisms. Proceedings of the nutrition society. 62; 129-134