When you have diabetes, it is important to keep blood sugar levels as stable as possible.
Good blood sugar control can help prevent or slow the progression of some of the main medical complications of diabetes (, ).
For this reason, avoiding or minimizing foods that cause big blood sugar spikes is essential.
Despite being a healthy fruit, bananas are pretty high in both carbs and sugar, the main nutrients that raise blood sugar levels.
So, should you be eating bananas if you have diabetes? How do they affect your blood sugar?
If you have diabetes, being aware of the amount and type of carbs in your diet is important.
This is because carbs raise your blood sugar level more than other nutrients, which means they can greatly affect your blood sugar control.
When blood sugar rises in non-diabetic people, the body produces insulin. It helps the body move sugar out of the blood and into the cells where it's used or stored.
However, this process doesn't work as it should in diabetics. Instead, either the body doesn't produce enough insulin or the cells are resistant to the insulin that is made.
If not managed properly, this can result in high-carb foods causing big blood sugar spikes or constantly high blood sugar levels, both of which are bad for your health.
A single medium-sized banana contains 14 grams of sugar and 6 grams of starch (3).
Bottom Line: Bananas are high in carbs, which cause blood sugar levels to rise more than other nutrients.
In addition to starch and sugar, a medium-sized banana contains 3 grams of fiber.
Everyone, including diabetics, should eat adequate amounts of dietary fiber due to its potential health benefits.
However, fiber is especially important for people with diabetes, as it can help slow the digestion and absorption of carbs ().
This can reduce blood sugar spikes and improve overall blood sugar control ().
One way of determining how a carb-containing food will affect blood sugars is by looking at its glycemic index (GI).
The glycemic index ranks foods based on how much and how quickly they raise blood sugar levels.
The scores run from 0 to 100 with the following classifications:
- Low GI: 55 or less.
- Medium GI: 56–69.
- High GI: 70–100.
Diets based on low-GI foods are thought to be particularly good for people with type 2 diabetes (, , , , ).
This is because low-GI foods are absorbed more slowly and cause a more gradual rise in blood sugar levels, rather than large spikes.
Overall, bananas score between low and medium on the GI scale (between 42–62, depending on the ripeness) (11).
Bottom Line: In addition to sugar and starch, bananas contain some fiber. This means that the sugars in bananas are more slowly digested and absorbed, which could prevent blood sugar spikes.
The type of carbs in your banana depends on the ripeness.
Green or unripe bananas contain less sugar and more resistant starch (, ).
Resistant starches are long chains of glucose (starch) that are "resistant" to digestion in the upper part of your digestive system ().
This means that they function in a similar way as fiber, and won't cause a rise in blood sugar levels.
However, they may help feed the friendly bacteria in your gut, which has been linked to improved metabolic health and better blood sugar control (, , , ).
In fact, a recent study on blood sugar control in women with type 2 diabetes found some interesting results. Those supplementing with resistant starch had better blood sugar control than those who didn't over an 8-week period ().
Other studies have found resistant starch to have beneficial effects in people with type 2 diabetes. These include improving insulin sensitivity and reducing inflammation (, , , ).
The role of resistant starch in type 1 diabetes is less clear.
Bottom Line: Green (unripe) bananas contain resistant starch, which doesn’t raise blood sugar and may even improve long-term blood sugar control.
Yellow or ripe bananas contain less resistant starch than green bananas and more sugar, which is more quickly absorbed than starch.
This means that fully ripe bananas have a higher GI and will cause your blood sugar to rise faster than green or unripe bananas ().
Bottom Line: Yellow, ripe bananas contain more sugar than green, unripe ones. This means they cause a bigger rise in your blood sugar level.
Ripeness isn't the only factor when it comes to the amount of sugar in your banana.
Size also matters. The bigger the banana, the more carbs you will be getting.
This means that a larger banana will have a greater effect on your blood sugar level.
This portion-size effect is called the glycemic load.
Glycemic load is calculated by multiplying the glycemic index of a food by the amount of carbs in a serving, then dividing that number by 100.
A score of less than 10 is considered low, 11–19 is medium and more than 20 is high.
Here's the approximate amount of carbs in the different sizes of bananas (3):
- Extra small banana (6 inches or less): 18.5 grams.
- Small banana (about 6–6.9 inches long): 23 grams.
- Medium banana (7–7.9 inches long): 27 grams.
- Large banana (8–8.9 inches long): 31 grams.
- Extra large banana (9 inches or longer): 35 grams.
If all these bananas were fully ripe (GI of 62), then their glycemic load would range from 11 for an extra small banana to 22 for an extra large banana.
To ensure you don't cause your blood sugar to rise too much, it's important to be aware of the size of the banana you're eating.
Bottom Line: The size of the banana you eat determines its effect on your blood sugar level. The larger the banana, the more carbs you'll consume and the greater the rise in your blood sugar will be.
Most generic dietary guidelines for diabetes recommend following a healthy, balanced diet which includes fruit (, , ).
This is because eating fruits and vegetables has been linked with better health and a lower risk of disease, such as heart disease and some cancers (, , ).
Diabetics are at an even greater risk of these diseases, so eating enough fruits and vegetables is important (, ).
Unlike refined sugar products like candies and cake, the carbs in fruit such as bananas come with fiber, antioxidants, vitamins and minerals.
More specifically, bananas provide you with fiber, potassium, vitamin B6 and vitamin C. They also contain some antioxidants and beneficial plant compounds ().
A recent study looked at the effect of limiting fruits on the blood sugar control of 63 people with type 2 diabetes ().
They found that advising people to eat no more than 2 pieces of fruit per day resulted in people eating less fruit.
However, they also found that eating less fruit did not improve blood sugar control, weight loss or waist circumference.
For most people with diabetes, fruits (including bananas) are a healthy choice.
If you are able to eat bananas, it's important to be mindful of the ripeness and size of the banana to reduce its effect on your blood sugar level.
Bottom Line: Fruits like bananas are a healthy food that contains fiber, vitamins and minerals. You can include bananas in your diet, even if you have diabetes.
If you have diabetes, it's perfectly possible to enjoy fruit such as bananas as part of a healthy diet.
If you like bananas, the following tips could help minimize their effects on your blood sugar levels:
- Watch your portion size: Eat a smaller banana to reduce the amount of sugar you eat in one sitting.
- Choose a firm, nearly-ripe banana: Pick a banana that's not overly ripe so that the sugar content is slightly lower.
- Spread your fruit intake throughout the day: Spread out your fruit intake to help reduce the glycemic load and keep your blood sugar stable.
- Eat them with other foods: Enjoy your bananas with other foods, such as nuts or full-fat yogurt, to help slow down the digestion and absorption of the sugar.
If you're diabetic, remember that all carb-containing foods can affect people's blood sugars differently.
Therefore, you might want to monitor how eating bananas affects your blood sugar and adjust your eating habits accordingly.