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Glycemic Index and Glycemic Load - How Does Food Affect Blood Sugar (Glucose) Levels and the After Eating Changes

Rajan is a botany and chemistry major. He has worked as a poultry breeder for 23 years, breeding layer and broiler parents.

changes in blood sugar levels brought about by  high GI and low GI foods

changes in blood sugar levels brought about by high GI and low GI foods

Anything and everything that we eat or drink is acted upon by the digestive juices and digested by the human body. Our body then has to decide in which of the following ways this has to be utilized.

  1. To provide energy.
  2. To store it as fat.

Our body has been so programmed genetically that whenever possible food is stored as fat since survival is of prime importance.
That said, the 2 factors responsible for the body to decide what to do with what we ingest are :

  • Glycemic Index (GI)
  • Glycemic Load (GL)

Let us now see what these 2 factors are, what they mean and why are they so important for us.

Glycemic Index (GI)

Whatever we eat is processed, metabolized and affects the body in many ways, including the following :

  • First, it raises blood glucose levels.
  • Second, this raised blood sugar levels affect insulin secretion.
  • Third, the fat storage mechanism is activated.
  • Fourth, it affects the pancreas - the insulin manufacturing and secreting organ.

In simple words, the Glycemic Index of a food is a number that tells us to what degree the carbohydrates in the food raise the blood sugar levels. This number has been determined by comparing it against the rise in blood sugar brought about by pure glucose.

Glucose has been given a GI of 100 and the Glycemic index of all foods have been rated with reference to it and have a GI lower than this.

When food is consumed, the carbohydrates in the food raise the blood sugar either quickly or slowly. Those foods that are digested fast, raise blood sugar rapidly and have a higher Glycemic Index than those that are digested slowly and raise blood sugar gradually and thus have a lower Glycemic Index.
It is interesting to note that the foods which raise blood sugar rapidly also tend to raise it to a higher level as compared to low GI foods.

So foods have, either, a high Glycemic Index or a low Glycemic Index.

Glycemic Index Of Foods & Additions That Can Affect Their GI

Foods with

  • GI up to 55 are Low GI foods -
    legumes/pulses, most fruits & vegetables, some whole grains, nuts, fructose, chickpeas, kidney beans, beets.
  • GI 56 - 69 are Medium GI foods -
    whole wheat products, sucrose, baked potatoes, sweet potato, basmati rice.
  • GI 70+ are High GI foods -
    white bread, white rice, cornflakes, maltose, glucose, all extruded breakfast cereals.

However, the glycemic effect of foods with a high glycemic index can vary with the addition of fat, protein, organic acids or their salts, etc.

For instance,

  • Adding vinegar reduces the GI of the food
  • Presence of fat or fibre slows down the absorption rate and lowers GI. Therefore bread that is coarse or has higher fibre content has a lower GI.
  • Consuming alcoholic beverages, excluding beer, just before a meal reduces the glycemic index of the food by as much as 15% as studies indicate.

What Do High Glycemic Index Foods Do ?

High GI foods

  • Raise blood sugar rapidly
  • Provide quick energy
  • Cause increased insulin release
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And the increased insulin causes,

  • A rapid drop in blood sugar levels
  • This reduces the energy supply and causes one to feel hungry

In addition to carbohydrates, the different levels of protein and fat in the ingested food also affect the metabolic response of the body to the food and alter its glycemic response.

If pure protein is consumed and no carbohydrates are, it causes an insulin response, especially in those having diabetes.

This can be seen in the case of milk, which is a potent insulin secretagogue, as studies have shown it to cause five times increased insulin response than what is expected from a glucose response. This is why, excess milk consumption in bottle-fed infants, leads to increased weight gain.

Similarly, when adults consume excess milk or protein and do little exercise it results in an increase in body fat and weight.

Studies also indicate that consuming more than 30 grams of protein at a time makes the calories so produced to be converted into fat, especially abdominal fat.

Risks Of High GI Foods

  • Higher risk of developing type 2 diabetes, coronary heart disease and macular degeneration.
  • High blood sugar levels also pose an increased risk to plaque deposition in the arteries as well as the risk of developing kidney disease,
  • Increased susceptibility to cancer.
  • Increased weight gain and predisposes to obesity.

To Sum Up

Everything we eat has a Glycemic index assigned to it.

  • High GI foods are digested quickly, raise blood sugar levels rapidly causing a rise in insulin secretion and levels and stimulate fat storage.
  • The consequent fall in blood sugar levels leads to a fall in energy levels causing hunger in varying degrees wanting one to eat again. Thus, repeating the cycle and causing more and more fat to be stored.
  • Makes the pancreas work harder and more.


Low GI foods

  • Are digested slowly thus release glucose gradually in the blood, cause a lower spike in blood sugar levels.
  • Do not stimulate fat storage.

Some Additional Points To Note

  • Foods with a low glycemic index can have high carbohydrate content or vice versa.
  • Glycemic index is not dependent on the amount of food consumed
  • All foods having high GI need not be avoided all the time. For instance, in times after strenuous activity like sports and exercise, the body needs rapid energy and more insulin to pump this glucose into the cells for repair. This is brought about by foods having high GI, like sports drinks, which the trainers and coaches advise.
  • The GI accuracy of the foods is variable as it depends on the varieties, ripeness, processing method, duration of cooking, storage time, etc.
  • The glycemic response also depends upon the individual response, depends on the blood glucose levels, insulin resistance etc.

These factors mentioned above are not within our control and the GI values have been worked out by feeding people who have been subjected to experimental test feeding of the specific foods and by the testing of the blood samples at different intervals of time.

All said and done, it has to be realised that of all the factors, the quantity of carbohydrates consumed ( and this is within our control), has the biggest bearing on blood sugar levels than Glycemic Index alone.

So, another factor, the Glycemic Load (GL) comes into the picture.

Glycemic Load (GL)

Glycemic Load, like the Glycemic Index, has a number attached to it but it is not a fixed number but varies according to the amount of food consumed.

Glycemic Load tells us the carbohydrates load we are consuming per serving of food.

A simple formula to determine the Glycemic Load of any food is :

GL = GI/100 multiplied by the net carbohydrates consumed.
( Net carbohydrates = Total carbohydrates minus the dietary fibre)

A Glycemic Load (GL) of 1 is equal to the Glycemic effect that 1 gram of glucose causes.

Standard diets have a total GL value from 60 - 180 per day.
It is important to keep the daily Glycemic load of less than 500.

Glycemic Index, Glycemic Load And The Third Factor

Since it has been shown in studies that repeated high levels of blood sugar and correspondingly high insulin levels cause increased risk to diabetes, managing the Glycemic Load ensures that these blood sugar spikes are avoided, thus avoiding type 2 diabetes.

This tool - the Glycemic Load - is extremely useful for controlling blood sugar levels, especially in diabetics.

Glycemic Load management also helps in controlling weight gain and obesity and reducing risk to cancer.

Also, along with Glycemic Index and Glycemic Load, the Calories contained in foods are also taken into account so as not to over-consume on fats & calories.

The following example will illustrate this well.

An Apple having a GI 38 and weighing 138 grams contains 16 grams of net carbs and has a GL of 6 (38/100x16).
A serving of 4 ounces of peanuts (113 grams) with a much lower GI of 14 and containing 15 grams of net carbs have a still lower GL of 2 (14/100x15).

On the face of it, a look at the Glycemic Load alone, peanuts would seem a better choice than apples. But it is not so! Why?

Because, in the quantities mentioned in the above example, Apples contain approximately 72 calories while peanuts contain more than 500 calories. That is over 400 calories more than in Apples.

These extra calories will not help in reducing weight.

The above example shows that ;

We have to keep in mind the Glycemic Index, the Glycemic Load and the Calories contained in the serving size of the food, to benefit fully from what we eat and avoid a lot of health issues like weight gain, obesity, diabetes, coronary heart disease and cancer.

Some Of My Other Health Articles


This article is research based and is for information purposes only. Please take the advice of your healthcare provider or medical doctor before you start to put any of the suggestions offered in this hub, into practice.

What Is Glycemic Index ?

Burden of the Glycemic Load

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2012 Rajan Singh Jolly


Rajan Singh Jolly (author) from From Mumbai, presently in Jalandhar, INDIA. on September 02, 2014:

Thanks Editor for pointing out the error. It stands corrected now.

Editor on August 29, 2014:

Under "Some additional points to consider" there is a grammatical error in this paragraph:

These factors mentioned above are not within are control and the GI values have been worked out by feeding people who have been subjected to experimental test feeding of the specific foods and by the testing of the blood samples at different intervals of time.

The second "are" should be "our".

Rajan Singh Jolly (author) from From Mumbai, presently in Jalandhar, INDIA. on October 03, 2013:


@GoForTheJuggler-thank you.

Joshua Patrick from Texas on October 01, 2013:

Great hub full of fantastic info - voted up and more!

FlourishAnyway from USA on October 01, 2013:

This is a great hub which explains the concepts well. Given the levels of diabetes these days, it's so important to develop a firm understanding of how what you eat impacts your body. Voted up and more.

Rajan Singh Jolly (author) from From Mumbai, presently in Jalandhar, INDIA. on August 23, 2012:

Hi tony,

I do hope the new drug that you are taking for your raised blood sugar works for you. thanks for sparing time to read and comment. Much appreciated.

Tony Mead from Yorkshire on August 23, 2012:


namasta, the suagr thing is difficult for most people to comprehend. I've been type 2 for ten years and still don't understand fully what is happeing with my blood sugar. It varies so much from day to day and at the moment it is quite high, I'm trying out a new injection which is not insulin and is supposed to help control the sugar and my weight. The jury is still out as to how effective it is.