What is Glycaemic Index and Glycaemic Load?

The Glycaemic Index (GI) indicates how fast the body converts carbohydrates from food into glucose. In other words, GI is a scale of carbohydrates in food, that analyses their impact on blood glucose levels.

The GI ranking of carbohydrates in food is from 0 to 100. Those carbohydrates that provoke a huge, fast spike in glucose levels are considered High GI. Medium GI provoke moderate rise and Low GI is assigned to carbohydrates that increase blood glucose levels slowly and very little. 

Breaking down the carbohydrates scale

Low GI food: 55 of less

Medium GI food: between 56 and 69

High GI food: 70 or more

Low GI food: almonds, blueberries, blackberries, strawberries, asparagus, celery, chicken breast, egg white, veal, fish, turkey, beef…

Medium GI food: sweet potatoes, prunes, bananas, pumpkin, walnuts, cheese (low fat), yoghurt (low fat), mangos, kiwi… 

High GI food: ketchup, coconut oil,  dates, watermelon, granola, white bread, pancakes, doughnuts, baguette, croissants, pizza, white rice…

Everyone knows that after eating a meal the blood sugar level changes, either just a little or dramatically. In either case, pancreas releases insulin to keep the blood glucose level in check. However, if pancreas has to continuously produce insulin because of excess blood sugar, that can lead to the insulin resistance. A pre-stage for people to develop diabetes type 2 and symptoms like constant hunger, weight gain or fatigue, among others. In fact, GI was initially developed as a tool for dietary management of type 1 diabetes. It was conceived in 1982, by a scientist named David Jenkins at the University of Toronto. Jenkins was investigating the impact of different carbohydrates on blood sugar levels.

Since then, many studies, books, nutritionists and health authorities have claimed a lot of benefits of the low GI diet, especially for diabetics, also for weight control or better sport performance.

In this scenario, it is logical to think that following a low GI diet is ideal to avoid dramatic spikes in the blood sugar levels. But, the reality is not than simple because there is another concept to consider, Glycaemic Load (GL). If GI focuses on the quality of carbohydrates, GL pays attention to the quantity.

Glycaemic Load

The glucose level elevates and drops after a meal that contains carbohydrates. How high it rises and how long it remains high, it depends on the quality of carbohydrate (GI), as well as the quantity. GL is the term used to describe the overall effect of these two factors on blood sugar. Thus, GL combines both the quantity and quality of carbohydrates. It is the best way to compare blood glucose values of different types and amounts of foods.

Glycaemic Load ranking 

Similar to the Glycaemic index, the GL of food can be classified as low, medium and high.

Low GL: 10 or less

Medium GL: 11-19

High GL: 20 or more

How to calculate GL?

Glycaemic Load = GI  x  carbohydrate (g) content per portion / 100

For example:

Carrots.

GI 92

Carbohydrates per serving 4.2 (80g)

92 x 4.2 / 100 = 3.8 GL

Sweet potato.

GI 48

Carbohydrates per serving 26 (150g)

48 x 26 / 100 = 12.48 GL

White pasta

GI 57

Carbohydrates per serving 44.3 (180g)

57 x 44.3 = 25.25 G

Which one is better to follow, GI or GL?

It is easy to go for Low GI food, but a combination of both may be the best to achieve greater health results.

To be considered 

There are many factors that affect carbohydrates and their impact on blood glucose levels. These factors are: how carbohydrates are cooked, how refined carbohydrates are, how others substances (fats, proteins, fibre) mixed with carbohydrates affect their absorption, which type of protein, animal or vegetable, is better to combine with carbohydrates to avoid huge spikes in blood sugar levels. What about fats?

As a conclusion and generally speaking, I would say that low, both GI and GL with some considerations, is always better. For optimal health, people should aim to keep their daily glycaemic load under 100. 

Remember, GI is for quality and GL is for quantity.