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Introduction

Many authors recommend additionally to their main principle (for example: counting calories) eating foods with low glycemic index. If you want to know why and what is glycemic index, keep on reading.

The Glycemic Index (GI) ranks carbohydrates according to their effect on blood glucose levels. Foods that raise your blood glucose level quickly have a higher GI rating than foods that raise your blood glucose level more slowly. A lower GI suggests slower rates of digestion and absorption of the sugars and starches in the foods. In general, the lower the rating, the better the quality of carbohydrate.

Not only do low GI foods raise your blood glucose more slowly and to a less dramatic peak than higher GI foods, but most low GI foods are all-around healthier choices. Low GI foods are usually lower in calories and fat, while also being high in fibers, nutrients and antioxidants. Choosing low GI foods more often may help you increase levels of HDL (healthy) cholesterol in your blood and might help you control your appetite, as they tend to keep you feeling fuller, longer.

Where the GI values come from?

The glycemic index of a food is defined by the area under the two hour blood glucose response curve following the ingestion of a fixed portion of carbohydrate (usually 50 g). The AUC (Area Under Curve) of the test food is divided by the AUC of the standard (either glucose or white bread, giving two different definitions) and multiplied by 100.

The average GI value is calculated from data collected in 10 human subjects. Both the standard and test food must contain an equal amount of available carbohydrate. The result gives a relative ranking for each tested food.

The current validated methods use glucose as the reference food, giving it a glycemic index value of 100 by definition. This has the advantages in that it is universal and it results in maximum GI values of approximately 100. White bread can also be used as a reference food, giving a different set of GI values (if white bread = 100, then glucose = 140).

The glycemic index can only be applied to foods with reasonable carbohydrate content, as the test relies on subjects consuming enough of the test food to yield about 50 g of available carbohydrate. Many fruits and vegetables (but not potatoes) contain very little carbohydrate per serving, or have very low GI values. This also applies to carrots, which were originally and incorrectly reported as having a high GI. Alcoholic beverages have been reported to have low GI values, however it should be noted that beer has a moderate GI. Recent studies have shown that the consumption of an alcoholic drink prior to a meal reduces the GI of the meal by approximately 15%.

GI division

GI values usually divided as the following table suggests:

Classification	GI range
Low GI	55 or less
Medium GI	56 - 69
High GI	70 or more

When high GI foods can become handy

A low GI food will release glucose more slowly and steadily. A high GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after endurance exercises. Also, high GL food will be appropriate for a person with diabetes experiencing hypoglycemia.

Endurance athletes such as ultra-marathoners and iron man triathletes have become increasingly aware of the glycemic index of foods taken before and during training and competition. In the hours before a competition athletes may consume foods with a lower GI value so that energy is released more slowly. During competition, the athlete may try to balance the consumption of high and low glycemic index foods to maintain constant energy levels and avoid "energy spikes".

GI and Weight control

Recent animal research provides compelling evidence that high GI carbohydrate is associated with increased risk of obesity. In human trials, it is typically difficult to separate the effects from GI and other potentially confounding factors such as fiber content, palatability, and compliance. In the study (Pawlak et al, 2004), male rats were split into high and low GI groups over 18 weeks while mean bodyweight was maintained. Rats fed the high GI diet were 71% fatter and had 8% less lean body mass than the low GI group. Post meal glycemia and insulin levels were significantly higher and plasma triglycerides were three-fold greater in the high GI fed rats. Furthermore, pancreatic islet cells suffered "severely disorganised architecture and extensive fibrosis". The evidence in this study showed that continued consumption of high glycemic index carbohydrates would likely have led to the development of severe metabolic abnormalities.

Choosing foods with a low GI rating more often than choosing those with a high GI may help you to:

Control your blood glucose levels
Control your cholesterol levels
Control your appetite
Lower your risk of getting heart disease
Lower your risk of getting type 2 diabetes

Common misunderstanding

A lower glycemic response is often thought to equate to a lower insulin demand, better long-term blood glucose control and a reduction in blood lipids. But in fact, some foods having a low glycemic index or having very little carbohydrate cause a high insulin response or raise blood lipids. The insulin index may therefore also be useful as it provides a direct measure of the insulin response to a food.

Important notes

The glycemic index is about the quality of the carbohydrates, not the quantity.
The glycemic index is about foods high in carbohydrates. Foods high in fat or protein don't cause your blood glucose level to rise much.
The GI of a food varies depending on the kind of food, its ripeness, the length of time it was stored, how it was cooked, its variety (potatoes from Australia, for example, have a much higher GI than potatoes from the United States, and how it was processed or manufactured.
The GI of a food varies from person to person and even in a single individual from day to day, depending on blood glucose levels, insulin resistance, and other factors.
If you choose a high GI food, combine it with a low GI food, for an overall medium GI meal. For example, half a bagel (high GI) with a bowl of chili (low GI), or corn flakes cereal (high GI) topped with a spoonful of All Bran (low GI) and some strawberries (low GI).
Most experts agree that what works best for people with diabetes - and probably the rest of us as well - is regular exercise, little saturated or trans fat (partially hydrogenated oils), and a high-fiber diet.