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Glycemic Index (GI)

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What is Glycemic Index (GI)?

GLYCEMIC INDEX (GI) is a scale which helps to rank carbohydrate- rich foods, depending on how they affect blood glucose levels, by comparing them to glucose.


In simple terms, GI measures how much your blood sugar level increases in a span of 2 - 3 hours after having food.

Glycemic Index

The scoring is between 0 to 100 with glucose being the reference food with a GI value   fixed at 100.  It is a new system of classifying carbohydrate containing foods, according to how quickly they raise blood glucose levels in the body.

The term ‘GLYCEMIC INDEX’ (GI) was first invented by David Jenkins & Thomas Wolever at St. Michael hospital in Toronto, Canada in 1981. Since then, it has been a subject of debate. More recently, an effort to expand GI has been made by Jennie Brand-miller & her associates in Sydney, Australia.

To better comprehend GI index, we need to understand that all carbohydrates, from starches to plain sugar (commonly called as “Table sugar”), share a basic biological property i.e. they can be digested and converted to glucose in our body.  The common misconception among the general public is that by avoiding  ‘plain sugar’ they can avoid diabetes and take care of their ‘sugar’ level in the blood.   I do not eat any ‘Mitha’ (‘Mitha’ means sugar in Hindi); is a common reply from the patients when they are asked to avoid sugar.  

When a doctor or dietician refers to ‘sugar’ in the food, they mean Carbohydrates and the patient understands it as table sugar. 

GI is possibly one of the scientific ways of looking at carbohydrate- rich food and finding out which item when consumed is likely to increase the level of glucose in the blood.


Carbohydrates with high GI causes a rapid increase of blood sugar, whereas diet based on low GI are low in sugar but high in fiber. They cause a slow rise of blood sugar and are, therefore, ideally suited for diabetic patients.

Here’s a quick overview of what’s high and what low In GI is

Classification GI Range Examples
Low GI 55 or less Most fruits and vegetables (except potatoes, watermelon), grainy bread, brown rice, fish, egg
Medium GI 56-69 Whole wheat products, basmati rice, sweet potato, table sugar, white rices
High GI 70 or more Flakes, rice krispies, baked potatoes, white bread, straight glucose (100)

Importance of Glycemic index

Our body has an obligatory requirement for glucose depending on metabolic demands of our body. It is usually around 200gms/day. Our brain completely depends on glucose and oxygen.

Maintaining a constant blood glucose level is important for our health and well-being. Both low or high levels can be dangerous, sometimes even fatal. If you are feeling lethargic and hungry during the day after hard work , it is most likely due to low blood glucose level.

  • Blood sugar level below 40mg/dl (known as ‘Hypoglycemia’ in medical terms) causes coma, stupor and even death.
  • Blood sugar level more than 180mg/dl (known as ‘Hyperglycemia’ in medical terms) causes long-term complication of diabetes mellitus.
  • Levels above 300 to 500 mgs/dl can cause acidosis and also lead to a state of coma Excess glucose that is stored is most often converted to fat. Food with high GI makes you initially feel very energetic but as the fat increases, with time, it makes you lethargic.

Research has shown that maintaining blood sugar levels, from a state where the blood sugar levels were fluctuating, does pay-off in the long run. The following are the benefits–

  • Lowers risk of heart disease.
  • Prevents Type 2 diabetes (Genetically determined diabetes where the individual body is resistant to insulin actions).
  • Help to evade serious side effects, if you have diabetes.
  • Curbs appetite, so you lose weight.
  • Helps to feel more energetic and this is important for a person’s well-being.

Glycemic Load (GL) of Food – While GI indicates the amount of glucose and the quality of food, GL indicates the quantity of food and it is calculated as:

GL = GI x Amount of Carbohydrates in gms / 100

GL of 10 or below are considered low whereas 20 or above are considered high. So if you love to eat food with High GI then try and consume very little for the purpose of your satiety, so that GL is kept less than 10.

Glycemic Index and Weight Loss

GLYCEMIC INDEX (GI ) diet programs are highly successful for weight loss and all diet plans for this are based on GI. For sustaining weight loss the person should have some knowledge about the foods that have high GI and avoid them. The common food includes refined carbohydrates (white bread), sweets, puddings, desserts, cakes, potato and rice to name a few.


Regular consumption of high GI diet not only increases the amount of food one eats but also the high calories in the diet causes rapid gain in weight of a person. A typical example is that of a hosteler who comes home for summer holidays, only to go back invariably after gaining weight. This is because of the pampering by parents and getting fed regularly with high GI food.

The Insulin Connection - A surge in glucose causes high secretions of insulin from the islets of Langerhans in your pancreas. The insulin helps to push the glucose inside the cell for its utilization. Constant insulin production results in overworked islets and eventually over a period of time results in diabetes. Keeping your glycemic load below 10 helps avoid diabetes and keeps your weight under control.

Effects of eating high GI food Effects of eating low GI foods
Cell dysfunction People tend to lose weight
Increased insulin production Increase the body’s sensitivity to insulin
Increased free fatty acid accumulation in body Reduce blood cholesterol levels
Raise the risk for obesity, type 2 diabetes and heart disease Reduce the risk of heart disease, reduce hunger, refuel carbohydrate stores after exercise


Once you have understood these basic concepts of GI plan out your diet sensibly. Speak to a dietician, tell them what food you like and what you don’t and they would help you with a diet plan for loosing weight. For diabetics, it is essential to understand these concepts to control their 'sugar' or rather glucose level in the blood.

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Latest Publications and Research on Glycemic Index

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Dr. Subhadeep Koner
Dr. Subhadeep Koner
4 years experience
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Sir It means all the foods with higher GI value should be avoided. But Beer has a high GI value but it is advised that it is an exception for it allows lower sugar turn out in blood sugar level. So how to make distinction. Thanks BNA

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