The glycemic index was formulated in 1981 by Dr. David Jenkins who at the time was a professor of nutrition based at the University of Toronto. He created the index as a method for diabetes patients to determine the effect carbohydrate food sources would have on their blood sugar levels.
Function
The body uses carbohydrates as its principal energy source. When you eat a carbohydrate food, the digestive system will break it down and sugar will be released into the bloodstream. The pancreas then produces insulin that will help the sugar get to the body cells where it can be used as energy. Carbohydrate foods do not all behave in an identical manner; some will break down rapidly and release glucose into the bloodstream very quickly, which can cause spikes in blood sugar and insulin levels. Others cause only slight fluctuations in blood sugar levels, and these food sources are therefore optimal for diabetes sufferers.
The glycemic index assigns a number to foods depending on how quickly sugar will be released after eating them. Foods with a high-GI reading release glucose swiftly, and low-ranking GI foods cause little change in blood sugar levels. Regularly eating high-glycemic index foods has also been linked to heart disease and obesity.
The GI and Weight Loss
As low-GI foods are digested more slowly, after eating them you are likely to feel satisfied for longer. This reduces the likelihood of eating between meals and also helps prevent premature hunger and food cravings. According to a study by Geoffrey Livesey published in the 2005 issue of Proceedings of the Nutrition Society, subjects who ate low-glycemic foods reduced their calorie intake and lost body fat of their own accord, although they were instructed they could eat as much as they wanted.
Controlling Food Cravings
When you haven't eaten anything for a while your blood sugar levels begin to drop, which results in a lack of energy. The brain also needs glucose to function, and it will send a request to the body for glucose. When this occurs, your likely reaction is to crave something sweet. The sweet food will cause blood sugar levels to rise quickly, and the pancreas will secrete insulin. When this occurs, blood sugar levels will drop again, and another food craving will occur. Therefore, eating low glycemic index foods can help regulate your blood insulin levels which will greatly assist in curbing food cravings.
Low GI Foods
To keep your blood sugar levels steady, you need to eat a large proportion of low-GI foods, or if you eat a high GI-food, you should combine it with lower-GI foods. Examples of fruits that rank low on the glycemic index include apples, grapefruits, kiwifruits and oranges. Low-GI vegetables include all leafy greens, cauliflower, carrots, Brussels sprouts and broccoli. Staple food choices on a low-GI diet include legumes, brown rice, pasta, pumpernickel bread and buckwheat. Protein-rich food sources such as meat, fish, dairy and eggs are not carbohydrate food sources and therefore are not listed on the glycemic index, as they do not cause spikes in blood sugar levels.
High GI Foods
Fruits with a high-GI include dates and watermelons. Parsnip, pumpkin and potatoes also rank highly. Any baked goods made with white refined flour such as french baguettes and donuts should be avoided on a low-GI diet. White rice and rice cakes have a high rating. In general, the more a food has been processed, the higher its GI rating will be.
References
- Mendosa: Glycemic Index Factor
- Toronto Region: University of Toronto Nutritional Sciences
- "Proceedings of the Nutrition Society": Low-Glycaemic Diets and Health: Low-glycaemic diets and health: implications for obesity; Geoffrey Livesey; 2005
- Mendosa: GI Lists
- University of Sydney: Glycemic Index Database
- Virgin Active Health Clubs: Glycaemic Index - Overcoming Food Cravings
