Go bananas, but go green for a lower glycemic index

People love their bananas. Ask anyone to grab a snack, and 9 times out of 10 they’ll pull out a banana from their backpack and pocketbook. In fact bananas are the most popular fruit in the US with the average person consuming 25 pounds a year.  They don’t need any washing or refrigeration. They are high in fiber and potassium, and low in calories. What could be wrong with them? Depending on the ripeness and size, a banana can have a huge impact on blood sugar. That can be a good thing if you are running a marathon, but a bad thing if you are watching your blood sugars or trying to lose weight. Bananas are not alone in spiking blood sugars; there are other  foods high on the glycemic index scale that do the same thing.

Glycemic index

Glycemic index (GI) is a scale used to measure the impact of a specific food on blood sugar. GI ranks food in comparison to a food reference point, either glucose or white bread, which are both ranked at 100. The GI of a food tells you how quickly the sugar from the food will enter the blood stream. Eating low GI foods have helped with weight loss as well as maintaining steady blood sugars in those with prediabetes or diabetes. Eating foods that keep blood sugars from spiking requires less insulin. A lower blood insulin level lessens the workload for the pancreas, preserving its function, and also helps with weight loss. Here are some examples of low, medium and high GI foods:

Low GI foods (up to 55)

  • 100% stone ground wheat bread or pumpernickel
  • Rolled or steel-cut oatmeal
  • Barley, bulgar, pasta, converted long grain rice
  • Sweet potato, peas, legumes, lentils, corn
  • Most fruits, non-starchy veggies, carrots

Medium GI foods (56-69)

  • Whole wheat, rye and pita bread
  • Quick oats
  • Brown, wild or basmati rice

High GI foods (70 and more)

  • Russet potatoes, pumpkin
  • White bread or bagel
  • Corn flakes, instant oatmeal, puffed rice, bran flakes
  • Pretzels, rice cakes, popcorn, saltines
  • Melons and pineapple

Glycemic load

Glycemin index is only part of the picture. To completely understand how much a food will impact blood sugar you also need to know how much sugar it will deliver. This is called the glycemic load. Glycemic load takes into consideration portion size. A glycemic load of 10 or below is considered low, while a glycemic load of 20 or more is considered high.

Glycemic index and glycemic load of bananas

higher GI ripe banana

ripe bananas are sweeter but also have a much higher GI

The American Journal of Clinical Nutrition maintains a list of glycemic index and glycemic load of over 750 common foods. The table below lists glycemic index, serving size based on grams, and glycemic load of a ripe banana, a slightly under-ripe banana and an over-ripe banana with some brown spots. I could not find any information on a fully green banana, but you can safely assume it has an even lower GI than the slightly under ripe banana.

Food Item

Glycemic Index

Serving Size (gms)

Glycemic Load

Ripe banana




Slightly under-ripe banana (yellow with green)




Overripe banana





A study reported in Diabetic Medicine on the effect of banana ripeness on blood sugars in people with type 2 diabetes, revealed:

slightly overripe bananas raised blood sugars nearly twice as much an under ripe ones.

What happens with ripening?

Green bananas contain more resistant starchesResistant starches are starches that resist digestion in the small intestine. Resistant starches are fermented by our healthy gut microbes and help to produce vitamins and health-promoting compounds as well as destroy potential cancer causing toxins. Resistant starches also help to reduce blood sugars.

When fruits ripen the resistant starches convert to sugar which is why a ripe banana tastes sweeter and will raise blood sugars much more than a green banana.

The size of the banana matters too

This is where Glycemic Load comes into play. A small banana has 18.5 gms of carbs, while a 9 inch banana contains over 35 gms. When you consider serving size in addition to ripeness, you can easily see how blood sugars could really spike by eating a large ripe banana.

What impacts glycemic index

Diabetes.org discusses other factors that impact the GI of foods.

  1. Ripeness and storage. The more a fruit or veggie ripens, the higher the GI.
  2. Processing. Juice has a higher GI than whole fruit. Mashed vegetables have a higher GI than whole veggies.
  3. Cooking time. Foods cooked longer have a higher GI. Al dente pasta, grains and beans have a lower GI.
  4. Food type. Converted long grain white rice has a lower GI than brown rice. But short grain white rice has a higher GI than brown rice

Aim for low GI foods for weight loss and better blood sugar control

I remember my mother telling me that green bananas would give me a stomach ache. Part of that problem is from the fermentation process that occurs in the gut. People with a normal digestion and a healthy diet should not experience this problem. But people with irritable bowel syndrome or some other digestive problem, green bananas could cause gas and bloating.

For the rest of us, unless you are getting ready for a marathon, this is what you should do:

  • Buy small bananas when they are more green.
  • Store bananas and other fruit in the refrigerator to slow down ripening. Although the banana peel will turn black, the banana won’t affected by the cold temperature.
  • And if you are trying to lose weight or have better blood sugar control, consider eating other fruits and veggies when they are more green, and go al dente as much as possible with your grains and pasta.


Barbara Groth

About Barbara Groth

I’m Barbara. I have always had a passion for helping people to feel good. As a nurse my early years were focused on getting sick people back to baseline. After becoming a diabetes educator and health coach my passion became raising that bar on the baseline – helping my clients to not only feel better but to look better and have a whole new outlook on life.