Glycaemic index & Glycaemic load: tools to help keep blood sugar levels under control
Glycaemic Index (GI) and Glycaemic Load (GL) are two phrases that you might have heard but do you understand what they are and should you pay any attention to them? Hopefully by the end of the article you will understand why they can be useful tools to help control your blood sugar and improve the way you eat.
The idea behind GI and GL is to help you choose foods that support blood sugar balance. In an ideal world, your blood sugar should change only within a narrow band over 24 hours. Your food choices are the main determinant of blood sugar shifts and some foods will cause greater spikes in blood sugar than others. The way in which we respond to food is highly variable from person to person, depending on factors, such as your physical activity, gut microbiome composition and genetics. Research in this area is evolving so whilst GI and GL can be useful tools, it may well be that in the future we have a more accurate way of measuring our individual glycaemic response to foods and meals.
Why is it a problem if my blood sugar has large spikes and dips throughout the day?
Elevated blood sugar after meals isn’t only a major risk factor for prediabetes and Type 2 diabetes but also linked to obesity, high blood pressure, non-alcoholic fatty liver disease and cardiovascular issues. If your diet contains large amounts of high GI or high GL food, you’re more likely to have these blood sugar spikes which puts you at greater risk from the conditions previously listed.
Recent research has found that the greater the drop in a person’s blood sugar 2-3 hours after a meal, the hungrier they were likely to be for their next meal. This led to a greater intake of calories at the subsequent meal. The largest dips in glucose tend to follow meals with the largest rise in glucose. This may help explain why foods that rapidly increase your blood glucose (such as sugar sweetened drinks or certain cereals) can lead to weight gain. When you eat low GI and GL foods you get a smaller rise in blood glucose that declines more gradually. This is why it can be useful to consider GI and GL.
Glycaemic Index and glycaemic load
Let’s take a more detailed look:
Glycaemic Index (GI) was first developed as a way of guiding food choices for people with diabetes. It refers to the impact of foods on blood sugar levels compared to a reference food (usually glucose). This index ranks carbohydrate containing foods on a scale of 1-100 depending how quickly they raise blood sugar levels when eaten on their own. Pure glucose (sugar) has a value of 100 and raises blood sugar very quickly. Low GI foods cause blood sugar levels to rise more slowly than high GI foods. In general, the more fibre or fat a food contains the lower its GI score will be. GI doesn’t take into account the portion size and will remain the same even if you double the amount of food.
Glycaemic Load (GL) is an extension of GI. It takes into account the GI and the portion size. It’s calculated by multiplying a food’s GI (as a %) by the number of net grams of carbohydrates (total carbohydrates minus fibre) in a meal or snack. It tells you how much a serving of that food is likely to increase your blood sugar levels.
If you’re attempting to lose or maintain weight or want to keep blood sugar levels balanced, Evergreen nutrition expert Ingrid Kitzing recommends a diet consisting of mainly low-GI and low-GL foods: “Try to ensure you don’t consume lots of foods with medium to high GI or GL values.” She says that “this will help keep blood glucose levels within the normal range and allow your body to function more easily without storing too much extra body fat or getting loads of food cravings.”
Low-GI and low-GL foods include:
- Non-starchy vegetables and fruit such as asparagus, broccoli, spinach, apples, blueberries and pears.
- Pulses such as lentils, kidney beans and chickpeas
It’s best to avoid high glycaemic foods or just consume them as an occasional treat. This includes sugary foods such as cakes, biscuits, sugary soft drinks (including fruit juices), some breakfast cereals and most white carbohydrates such as bread, pasta and rice.
You can look up the GI and GL of particular foods here. Remember that meat, poultry, fish, avocados, salad vegetables, cheese and eggs contain zero or minimal amounts of carbohydrates and so have no GI values as they don’t significantly impact blood sugar levels.
Not all low GI / GL foods are healthy and not all high GI / GL foods are unhealthy
Just because a food is low GI and/or low GL doesn’t mean it’s healthy. For instance, milk chocolate has a low GI due to its high fat content (which helps to smooth out the impact of the carbohydrates on blood sugar). Despite this, it’s still high in sugar and so should be kept to a minimum or avoided when trying to lose weight.
If we take a food such as watermelon with a high GI of 76 you might think that you should avoid it completely. However, when you take into account the average serving size of 1 cup it actually has a low GL of 8. So, just because a food is high or low on one measure doesn’t automatically mean it’ll the same on the other.
How you prepare your food can impact the GI and GL
In general, wholegrain pasta has a low GI because of its unique chemical structure but how you cook your pasta will impact the GI. Aim to eat your pasta al dente (firm) as overcooking will boost the GI.
Potatoes are usually high GI but there’s a way to reduce this. A potato salad made the day before and stored in the fridge overnight will have a lower GI than freshly boiled potatoes. When you store cooked potatoes at 4 degrees Celsius for up to 48 hours you increase something called resistant starch (a type of dietary fibre) which results in a lower GI and GL.
When you juice fruits or vegetables the glycaemic impact will increase because you’ve taken out the blood sugar friendly fibre and are consuming greater quantities than you would if you ate the whole food. This is why fibre rich smoothies are preferable to juices.
In summary, both GI and GL can help guide food choices from a blood sugar perspective but they tell you nothing about the nutrient content or the calorific value of the food. So, whilst they’re useful tools, they’re just one of many factors to consider when following a healthy diet.
Take control of your health today
If you’re a diabetic and regularly monitor your glucose levels, did you know you can easily keep track of your levels in the Evergreen Life app? You can monitor this over time and work out what’s affecting them.
Reviewed by:
Anna Keeble MA BA Wellbeing Expert
Dr Claire Marie Thomas MRCGP DFSRH DTMH DipNLP MBChB BMedSci Medical Expert
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