Do you enjoy blueberries but you’re worried that they may spike your blood sugars? Or worse, maybe someone has told you that you should never eat blueberries (or fruits in general) because they are harmful for your diabetes?
There is a lot of misinformation out there about how fruits like blueberries fit into a person with diabetes’ diet, but we are here to set the record straight today.
The good news is that blueberries are low on the glycemic index and come with a ton of impressive benefits. They aren’t known as a “superfood” for nothing.
In this blog post, we will look at where blueberries fit on the glycemic index, how they will affect your blood sugars, and why they are actually a great food to consider for someone with diabetes.
DISCLAIMER: This post was written by Justine Chan MHSc, RD, CDE. All content on this site is for informational purposes only and is not a substitute for professional medical or nutritional advice. Always seek medical and dietary advice from your doctor or dietitian.
Table of Contents
Blueberries and glycemic index
Blueberries have a glycemic index (GI) of 53 (1). Since scores under 55 are considered to be low on the glycemic index, that means blueberries are a low GI fruit. This is great news for you, since it means that blueberries should only cause a small rise in your blood sugar.
Glycemic index of blueberries compared to other fruits
Fruits fall in a wide range on the glycemic index, from the humble pear with a GI of 24 (2) to the flashy pineapple with a GI of 82 (3). Since blueberries have a GI of 53, this puts them right in the middle, along with oranges at 45 and bananas at 47 (3).
Keep in mind that some of these values should be taken with a grain of salt, since many GI values have only been tested in a limited number of people and food processing varies by country (3).
What is the glycemic index?
The glycemic index is a scoring system that measures the impact of a food on your blood sugars. It compares the food’s carbohydrate impact to the equivalent in sugar, giving you a range from 1 to 100.
In less scientific terms, if you see a GI of X, it means ‘If I eat this food, the sugars and starches in it will make my blood sugars go up X percent of what the same amount of sugar would do’. As a result, foods with a high GI score tend to raise blood sugars higher and faster than those with a low score.
Glycemic index ranges
Foods with carbs fall into three categories on the glycemic index: low, medium, and high. The ranges for these scores are:
Low GI: 1-55
Medium GI: 56-69
High GI: 70 or higher
As you can see, the glycemic index is helpful to see how different foods can affect blood sugar, but it doesn’t factor in how much of that food you are eating. Eating a pint of blueberries will impact your blood sugar more than eating just 10, even though the GI is still 53 in both cases! You need another way to figure out potency that also factors in the serving size.
This is where the glycemic load comes into play.
Blueberries and glycemic load
Glycemic load (GL) works a little bit differently from the glycemic index, because it combines the amount of the food you are eating to the glycemic index of the food. Let’s look at some common amounts that people eat and the glycemic load of each.
As a topping, a ¼ cup serving of blueberries has a GL of 2.4. This is the perfect amount to top your oatmeal in the morning or to add to yogurt.
As a snack, a 1 cup serving has a GL of 9.5.
Either of these options would be considered low GL. But what exactly does this mean?
When it comes to your blood sugars, glycemic load is the total package. It combines the GI of a food with the amount of the food you are eating. You can calculate it by multiplying the number of available carbs in your serving by the glycemic index of the food, divided by 100 (3) or:
GLFood = (GIFood x amount (g) of available carbohydrateFood per serving)/100
Once you have your glycemic load for your serving, you can then compare it to the chart below to see how much of an effect it will have.
Low GL: less than or equal to 10
Medium GL: 11-19
High GL: greater than or equal to 20
As a result, we now have a more complete picture of how the amount of a food will affect our blood sugars. In other words, the GL of a food considers both how quickly a food raises your sugar and the amount of carbs in the amount you are going to eat.
Using the glycemic load
Here’s an example. Let’s say, you are deciding on a topping for your oatmeal in the morning. You want to decide between a tsp of sugar or a ¼ cup of blueberries. They both have the same amount of carbs, 5g.
Obviously, the blueberries are going to be a better choice. How much better will it be? And if you choose sugar, how much of an effect will it have?
The glycemic index for sugar is 100 and the glycemic load works out to be 5 for one tsp. In contrast, the glycemic index for blueberries is 53 and the glycemic load is 2.4 for a quarter cup, about half of the effect.
It’s interesting to note that both options have a low glycemic load. That said, you’re going to get an entire quarter cup of blueberries to enjoy versus only a tsp of sugar!
Downsides of glycemic load
Using this tool will give you a much better idea of how much your blood sugar will rise and how long it will remain high after eating a specific food, but it’s probably not realistic to use day to day. After all, it’s unlikely you’re going to sit down at a restaurant, look up the glycemic index, carb counts of all the choices you’re considering, and start calculating the glycemic loads!
Also, it doesn’t account for the other foods you may be eating at a meal. As you probably already know, fat, protein, and fiber all affect how carbs are digested and absorbed.
Having said that, if you use it to keep one to two meals in the low range, you’ll likely meet the recommended glycemic load of less than 100 per day (4).
Are blueberries good for diabetes?
Here’s what 1 cup of blueberries (about 65 to 70 in total) provides (5):
- 18g net carbohydrates
- 3.5g fibre
- 1.1g protein
- 0.5g fat
They’re also a source of vitamins and minerals, some of which can help with the digestion of carbs as well as regulate your blood sugars. According to the USDA, 1 cup of blueberries contains (6):
- vitamin K (24% Daily Value)
- manganese (22% Daily Value)
- vitamin A (3% Daily Value)
- vitamin C (16% Daily Value)
- potassium (2% Daily Value)
- B vitamins (2-4% Daily Value)
- vitamin E (6% Daily Value)
In case you’re wondering, there is promising research that suggests that vitamin k and vitamin C both play a role in lowering post meal blood sugars for prediabetes and type 2 diabetes (7, 8). And according to this 2021 review (9), there is a connection between vitamin deficiencies, particularly A, C, D, E, and B-vitamins and unbalanced blood sugars.
But can’t you just use a multivitamin or supplement to get the same effect? Yes, but the truth is that foods like blueberries are full of vitamins and offer so much more than a vitamin would.
So where do the health benefits of blueberries come from? Well, you can thank their anthocyanins for that. Compared to other fruits, blueberries have the highest amount of anthocyanins. This is what gives them their trademark blue colour!
Let’s see what else the research says about this wonderful berry!
Diabetes: what the research says
Let’s first dive into the ‘gold star’ research – the randomized clinical trials. There aren’t a whole lot of clinical trials on blueberries and people with diabetes, but the few we have look promising.
Recently, there was a double blind randomized controlled trial involving 52 people with type 2 diabetes. The researchers divided the group in two, and gave half of the participants 22g freeze dried blueberries (the equivalent of 1 cup fresh) and the other half a placebo. Guess what? Those in the blueberry group were found to have lower A1c, triglycerides, and liver enzymes after 8 weeks (12). In other words, this study showed that eating blueberries can help with improving blood sugars, cholesterol and liver health.
Another randomized clinical trial published in 2022 looked at 34 women with a previous history of gestational diabetes and divided them into two groups. Both groups met biweekly with a dietitian and nurse practitioner, but one group was given 2 cups of frozen blueberries as a snack and a fibre supplement daily. Those in the blueberry group were less likely to gain excessive weight and had lower blood sugars after 18 weeks (13).
Ok, moving on to studies that are observational and involve studying large groups of people over time and tracking their health. What they have found is that a higher intake of blueberries is associated with less body fat, weight gain, and even a lower risk of type 2 diabetes (14).
So what’s the key takeaway? Blueberries have the potential to lower your blood sugars and keep the weight off. Just another reason to enjoy your blueberries!
How to incorporate blueberries in your diet
If you’re still not convinced about blueberries, try pairing it with the following low GI or non-carbohydrate foods:
- cottage cheese
- greek yogurt
- steelcut oats
- whip cream
- shredded coconut
- chia pudding
- salad mix
Key takeaways: blueberries and glycemic index
To summarize, blueberries have a glycemic index of 53 and are a low GI food. As both a snack and a topping they also have a low glycemic load.
While the glycemic index and load can help you to appreciate how a food can affect your blood sugars, it’s just one tool out of many that you can use to manage your diabetes. Try not to get too hung up on the numbers.
Also, there is some promising research linking the anthocyanins in blueberries to reduced blood sugars, and we covered what to pair blueberries with for your meals or snacks. Focus on including protein or fiber to help further curb the blood sugar rise and play around with the amounts to have.
All this, and they are delicious as well? What’s not to love!
Do you have someone you know who loves blueberries but is worried about their blood sugars? Give them a heads up and share this post!