What Exactly Is Glycaemic Index (GI)?
Alpro nutritionist explain how GI relates to blood sugar and what it means for your everyday food choices
You’re standing in the supermarket comparing two foods. One says “low GI”. Another says “whole grain”. A third talks about being high in fibre.
So, which one is actually better for your blood sugar?
You may have heard that foods with a high Glycaemic Index (GI) are “bad”, while low-GI foods are automatically the healthier choice. It sounds straightforward. Choose the lowest number and you’re done.
But GI doesn’t quite work that way.
GI can be a useful tool for understanding how carbohydrate-containing foods affect blood glucose, but it only tells you one part of the nutritional story.
Let’s look at what the Glycaemic Index actually means.
What Exactly Is the Glycaemic Index?
The Glycaemic Index (GI) is a way of classifying carbohydrate-containing foods according to how they affect blood glucose after eating.
In standard GI testing, a food containing a fixed amount of available carbohydrate is eaten and the rise in blood glucose over the following two hours is measured. That response is then compared with a reference food, usually glucose, which is assigned a GI value of 100.
In practical terms, foods are generally grouped as:
- Low GI: 55 or below
- Medium GI: 56–69
- High GI: 70 or above
Malaysian Ministry of Health materials similarly classify foods according to their effect on blood glucose and provide GI categories and examples for common foods.
A lower GI generally means the carbohydrate in that food produces a slower or smaller rise in blood glucose compared with a higher-GI food containing the same amount of available carbohydrate.
This is why GI is mainly relevant to foods containing carbohydrates. Different carbohydrate foods can behave quite differently once we eat them.
What Happens to Your Blood Sugar After You Eat?
When you eat carbohydrates, your body breaks much of them down into glucose.
That glucose enters your bloodstream, causing your blood glucose level to rise. Your body then uses hormones, particularly insulin, to help regulate glucose and allow it to be used or stored by your cells.
But carbohydrates aren’t all digested and absorbed in exactly the same way.
The structure of the food, degree of processing, type of starch, fibre content and other components of a meal can all influence the resulting blood glucose response. WHO also recognises digestibility and dietary fibre as important aspects of carbohydrate quality.
This is where GI becomes useful
Think about two carbohydrate foods containing the same amount of available carbohydrate. One might be digested relatively quickly and produce a sharper glucose response, while another may produce a more gradual response.
GI gives us a standardised way of comparing those responses.
Does a Higher GI Mean a Food Is Unhealthy?
Not necessarily.
This is where a lot of confusion comes in.
It can be tempting to treat GI like a health score:
Low number = good. High number = bad.
But GI wasn’t designed to tell you whether a food is healthy or unhealthy overall. What it tells you is how the carbohydrate in that food affects your blood sugar after you eat it.
A food’s overall nutritional value also depends on factors such as its fibre content, degree of processing, micronutrients, fat quality, sodium, added sugars and the amount you actually eat.
That’s why Malaysian guidance emphasises that even when higher-GI foods are replaced with lower-GI choices, the principles of a healthy diet still need to be followed.
WHO takes a similarly broader approach to carbohydrate quality. Its guidance recommends obtaining carbohydrates primarily from whole grains, vegetables, fruits and pulses, while also emphasising naturally occurring dietary fibre.
So instead of asking only:
“What’s the GI?”
A more useful question is:
“What happens to my blood sugar when I eat this — and what else does this food provide?”
What Should You Actually Look For When Choosing Food?
Instead of shopping according to one number, take a broader view.
Look at carbohydrate quality. WHO recommends that carbohydrate intake come primarily from whole grains, vegetables, fruits and pulses.
Consider fibre. Fibre is another important part of carbohydrate quality. WHO recommends that adults consume at least 25 g of naturally occurring dietary fibre each day.
Consider how much carbohydrate you’re eating. A low-GI label doesn’t make portion size irrelevant. The amount of carbohydrate you consume still contributes to your overall blood glucose response.
Look beyond GI. Check the overall nutrition information and ingredients rather than judging a food solely by its GI value.
Think about the whole meal. We rarely eat individual carbohydrate foods completely on their own. Malaysian guidance on incorporating GI into meals also considers factors such as fibre, protein and healthy oils as part of the overall meal.
The practical rule is quite simple:
Don’t use GI as a pass-or-fail test for food. Use it as one piece of information that helps you make a more informed choice.
Who Should Pay Closer Attention to GI?
GI may be particularly useful for people who need to pay closer attention to their blood glucose, including people living with diabetes.
However, individual glucose responses aren’t identical, and GI should not replace personalised advice from your healthcare professional.
If you have diabetes and take insulin or glucose-lowering medication, speak with your doctor, pharmacist, dietitian or nutritionist before making substantial changes to your carbohydrate intake, particularly if your medication or insulin dose is related to your food intake.
Your healthcare professional can help you consider GI alongside factors specific to you, such as portion sizes, medication, glucose readings and your overall dietary pattern.
Quick Recap
GI tells you about a food's effect on blood glucose. It compares the blood glucose response from carbohydrate-containing foods under standardised conditions.
Low GI generally means a slower or smaller blood glucose response. Foods are commonly classified as low, medium or high GI according to their GI value.
Similar foods don't necessarily have the same GI. Ingredients, processing, food structure and preparation can influence glycaemic response.
Look at the bigger nutritional picture. GI, carbohydrate amount, fibre, ingredients, portion size and your overall dietary pattern all matter when making everyday food choices.
Low GI and low carbohydrate aren’t the same thing. GI and carbohydrate amount provide different information, so it is useful to consider both.
Looking for an everyday bread that considers both low GI and low in carbs?
Alpro LowCarb Sourdough contains 40% less carbohydrate compared with white bread and has a tested low GI of 37. It is also high in fibre and protein, giving you more than one nutritional factor to consider when choosing your everyday bread.
Discover Alpro LowCarb Sourdough and find out how to order through the link below.
https://alpropharmacy.com.my/pages/lowcarb-sourdough-bread
Still Unsure What Glycaemic Index Means for You?
Understanding a GI number is one thing. Knowing how to apply it to your usual meals, food choices or blood glucose management can be more complicated.
Our pharmacists, dietitians and nutritionists at Alpro Pharmacy can help you understand how GI and carbohydrate choices may fit your individual needs, particularly if you’re managing diabetes or monitoring your blood glucose.
References
- Ministry of Health Malaysia. Clinical Practice Guidelines: Management of Type 2 Diabetes Mellitus. Ministry of Health Malaysia. Glycaemic Index guidance and food classifications. Ministry of Health Malaysia GI guidance
- Ministry of Health Malaysia. Management of Type 1 Diabetes Mellitus in Children & Adolescents. Appendix: Glycaemic Index for Local Malaysian Foods. Ministry of Health Malaysia. Ministry of Health Malaysia
- World Health Organization. (2023). Carbohydrate intake for adults and children: WHO guideline. Geneva: World Health Organization. ISBN 978-92-4-007359-3. WHO carbohydrate guideline
- World Health Organization. (2023). WHO updates guidelines on fats and carbohydrates. World Health Organization, 17 July 2023. WHO guidance summary
- Chiavaroli L, Lee D, Ahmed A, Cheung A, Khan TA, Blanco S, et al. (2021). Effect of low glycaemic index or load dietary patterns on glycaemic control and cardiometabolic risk factors in diabetes: systematic review and meta-analysis of randomised controlled trials. BMJ, 374. DOI: 10.1136/bmj.n1651. BMJ systematic review and meta-analysis
