Glycemic index ?

Glycemic index (also glycaemic index, GI) is a ranking system for carbohydrates based on their effect on blood glucose levels. It compares available carbohydrates gram for gram in individual foods, providing a numerical, evidence-based index of postprandial (post-meal) glycemia. The concept was invented by Dr. David J. Jenkins and colleagues in 1981 at the University of Toronto.

Carbohydrates that break down rapidly during digestion have the highest glycemic indices. Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have a low glycemic index. A lower glycemic index suggests slower rates of digestion and absorption of the sugars and starches in the foods and may also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion. 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.

Glycemic index of foods

GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:

Classification	GI range	Examples
Low GI	55 or less	most fruit and vegetables (excepting root vegetables), oats, buckwheat, whole barley, All-bran,
Medium GI	56 - 69	sucrose, candy bar, croissant, brown rice
High GI	70 or more	corn flakes, baked potato, Jasmine rice, white bread, white rice

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 exercise or for a person with diabetes experiencing hypoglycemia.

The glycemic effect of foods depends on a number of factors such as the type of starch (amylose vs. amylopectin), physical entrapment of the starch molecules within the food, fat and protein content of the food and organic acids or their salts in the meal — adding vinegar for example, will lower the GI. The presence of fat or soluble dietary fibre can slower gastric emptying rate thus lowering the GI. Unrefined breads with higher amounts of fibre generally have a lower GI value than white breads. Many brown breads, however, are treated with enzymes to soften the crust, which makes the starch more accessible. This raises the GI, with some brown breads even having GI values over 100.

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 fibre 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. Postmeal 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 disorganized 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.

While adding butter or oil will lower the GI of meal, the GI ranking does not change. That is, with or without additions, there is still a higher blood glucose curve after white bread than after low GI bread such as pumpernickel. List of foods with low index rating.

1. Vegetables (at least 5 portions a day)
2. Gross bread, grain, pasta, and other low glycemic, amyloid food (3–6 portions daily)
3. Fruit (2–3 times a day)
4. Nuts, seeds and shell fruits (eat 1–3 times a day), and oils pressed from these (1–2 times a day)
5. Pure proteins like meat, fish, poultry, eggs (up to 2 portions daily — red meat not more than 1–2 times a day)
6. Dairy products (1–2 portions daily, preferably low-fat products)
7. White bread, rice, potatoes, sweets (cookies and cakes) — eat rarely