Green banana benefits: resistant starch, gut health and blood sugar

Green bananas are having a moment. People online are eating them raw, blending them into smoothies and calling them a "bitter green banana" hack for weight loss and gut health. Meanwhile, in Indian, Caribbean and African kitchens, green bananas have been cooked as a vegetable for generations.

So what's the real story? The short version: green banana benefits mostly come from one thing, resistant starch, a type of starch that acts more like fibre than sugar. It feeds your gut bacteria and doesn't spike blood sugar the way a ripe banana can. Below we cover green banana nutrition, what the research actually shows, weight loss vs weight gain, side effects, and easy ways to eat them.

What is resistant starch (RS2)?

Most starch, like the starch in bread or potatoes, gets broken down into glucose in your small intestine. Resistant starch "resists" that. It passes through to your large intestine mostly intact, where your gut bacteria ferment it. That's why it behaves a lot like fibre.

There are a few types. The ones that matter here:

• RS2: starch in its natural raw form, packed in tight granules your enzymes can't easily get into. Green bananas and raw potato are the classic examples.
• RS3: starch that has been cooked and then cooled, which makes some of it re-form into a resistant shape. Cold cooked rice, cooled potatoes and cooled cooked green banana all contain some.
• RS1 and RS4/RS5: starch trapped in whole grains and seeds, and specially modified starches used in food manufacturing.

When gut bacteria ferment resistant starch, they produce short-chain fatty acids, especially butyrate. Butyrate is the main fuel for the cells lining your colon, and it's a big reason researchers are interested in resistant starch for gut health.

Green banana nutrition vs yellow banana

Here's the key thing to understand. A green banana and a yellow banana have about the same calories and nutrients. What changes is the type of carbohydrate. In a very green banana, most of the carbs are starch, and much of that is resistant starch. As it ripens, enzymes turn that starch into sugar. By the time it's yellow with brown spots, most of the starch has become sugar, which is why ripe bananas taste so much sweeter.

Ripe banana values: USDA FoodData Central, "Bananas, raw" (FDC 173944). Green banana values change with ripeness, so they are shown as a comparison rather than exact numbers.

Bananas also give you vitamin B6 (a medium banana has about a quarter of your daily needs), some vitamin C, magnesium and plenty of potassium, whether green or yellow.

Green banana benefits: what the research says

A 2019 systematic review of green banana studies in children and adults found most of them reported benefits, mainly for digestion, blood sugar and feeling full. But many studies were small and used different products (green banana pulp, flour or starch), so the results are promising rather than proven. Here's the breakdown.

1. A healthier gut and a thriving microbiome

This is where green bananas shine. Resistant starch is a prebiotic: it feeds the friendly bacteria in your large intestine, which turn it into butyrate and other short-chain fatty acids. In lab and animal studies, green banana flour raised levels of acetate, propionate and butyrate. A more diverse, well-fed microbiome is linked with better gut health overall, though human research on specific outcomes is still growing.

2. Help with diarrhoea in children

Some of the most interesting research comes from Bangladesh, where cooked green banana was added to the diet of young children with persistent diarrhoea. The children who got green banana recovered faster than those who didn't. It's an old remedy in many countries, and the science backs it up for this use. Note that this was under medical supervision, alongside rehydration, not instead of it.

3. Steadier blood sugar

Because resistant starch isn't turned into glucose in the small intestine, green bananas cause a smaller, slower rise in blood sugar than ripe ones. Underripe bananas have a lower glycaemic index (GI) than ripe bananas. Studies with green banana flour in healthy adults and in people with type 2 diabetes have found better glucose control and improved insulin sensitivity. If you have diabetes, green bananas can be a better choice than very ripe ones, but they still contain carbs, so count them as part of your meal.

4. Feeling fuller for longer

Resistant starch and fibre slow digestion and may increase fullness hormones. In studies, adults who had green banana flour felt more satisfied and ate a bit less afterwards. That's a real but modest effect.

5. Regularity

Green banana has been studied for constipation as well as diarrhoea. Some children's studies found it helped both, which makes sense for something that adds bulk and feeds gut bacteria. Results in adults are mixed, and too much resistant starch can actually make some people more constipated (see side effects below).

Bitter green banana for weight loss: does it work?

The "bitter green banana" trend says eating unripe bananas will help you lose weight. Here's the honest take.

• Green bananas can help a little. They're filling, low in sugar and slow to digest, so they may help you eat less. In some studies of people with type 2 diabetes, green banana flour was linked with a small drop in body weight.
• They are not a fat burner. No food melts fat. Weight loss still comes down to your overall diet, activity and sleep.
• The bitterness isn't the magic part. Raw green bananas taste bitter and dry in your mouth because of tannins, the same compounds that make strong tea astringent. The benefit comes from the resistant starch, not the bitter taste, so there's no need to force down raw ones.

Banana: weight gain or weight loss?

Neither, on its own. A medium banana has about 105 calories, about the same as a slice of toast with a little butter. Eaten as a snack instead of biscuits or crisps, bananas can help with weight loss. Eating several a day on top of everything else adds calories like any food would. Green bananas just give you more fullness and less sugar for the same calories.

Green banana side effects and who should be careful

Green bananas are safe for most people, especially cooked. A few things to know:

• Gas and bloating. The most common one. Your gut bacteria are fermenting a lot of new starch. Start with half a green banana or a tablespoon of green banana flour and build up over a couple of weeks.
• Constipation. Some people find large amounts of resistant starch bind them up. Drink enough water and don't go overboard.
• Hard to digest raw. Raw green bananas are very starchy, dry and astringent. Most cultures cook them. If you eat them raw, keep portions small.
• Latex-fruit allergy. People allergic to latex sometimes react to bananas (and avocado, kiwi and chestnut). Green bananas also have more sticky latex sap in the peel.
• Kidney disease. Bananas are high in potassium. If you've been told to limit potassium, ask your doctor or dietitian how much banana is OK.
• IBS. Some people with IBS do well with green bananas; others find fermentable starches trigger symptoms. Try a small amount first.

Are green bananas safe to eat raw?

Yes, they're not toxic, but they're not very pleasant either. A fully green banana is hard, chalky and leaves your mouth dry. Most of the world eats green bananas cooked: boiled, steamed, curried or fried. If you want the raw-starch benefit without the struggle, two easy options:

• Eat bananas slightly green. Yellow with green tips still has a decent amount of resistant starch and tastes fine.
• Use green banana flour. Stir it into smoothies, yoghurt or porridge (don't cook it if you want to keep the RS2). Start with about a tablespoon a day and build up slowly.

Does cooking destroy the resistant starch?

Partly. Heat breaks open the starch granules (RS2), so cooked green banana has less resistant starch than raw. But when cooked starch cools, some of it re-forms into RS3. So boiling green bananas and letting them cool, for a salad or to reheat later, still gives you a useful amount. And even hot, cooked green banana is lower in sugar than ripe banana.

How to eat green bananas

How to peel a green banana

1. Cut off both ends.
2. Run a knife down the length of the peel along a ridge, just deep enough to cut the skin.
3. Prise the peel off sideways with your thumb. If it's stubborn, boil the banana in its skin for 10 to 15 minutes first and the peel slides off.
4. Oil your hands or wear gloves. The sticky sap stains skin and clothes.

Easy ways to use them

• Boiled: boil in their skins for 15 to 20 minutes, peel, and eat with salt, lime and a drizzle of oil, or mash like potatoes.
• Green banana salad: boil, cool, slice and toss with onion, herbs, lime and olive oil. Cooling boosts the RS3. Full method: green banana salad.
• Curry: cube and simmer in any vegetable curry or dal. Green banana holds its shape well.
• Smoothie: half a slightly green banana or a spoon of green banana flour with berries, yoghurt and oats.
• Baked chips: slice thinly, toss with a little oil and salt, and bake until crisp. Lighter than fried. See our baked green banana chips.

Raw banana in Indian cooking and Ayurveda

In India, raw banana (kaccha kela, vazhakkai in Tamil, kancha kola in Bengali) is treated as a vegetable, not a fruit. It's used in sabzi, poriyal, kofta, cutlets, chips and curries. In traditional Ayurvedic practice, raw banana is generally seen as a filling, "binding" food that is often given for loose stools, which lines up nicely with the modern diarrhoea research. These are traditional views rather than tested claims, but the cooking is delicious either way.

Want to try it? Our raw banana sabzi is an easy everyday North Indian version with a little turmeric, and the South Indian raw banana fry is crisp and spicy. Both are great with dal and rice.

Green banana recipes

Four easy ways to cook green bananas, from an Indian sabzi to a cooled salad (cooling keeps more resistant starch) and crunchy baked chips:

How green banana fits into a healthy diet

Green bananas are a handy, cheap way to get more resistant starch, but they work best as part of a varied diet with plenty of other fibre: oats, beans, lentils, whole grains, vegetables and fruit. If you want ideas, see our guides to a balanced breakfast, overnight oats and building a healthy bowl. Start slow, cook them the way you enjoy, and let your gut get used to them.

Green banana questions people ask

Are green bananas better than yellow bananas?

Not better, just different. Green bananas have more resistant starch and less sugar, so they're gentler on blood sugar and better for feeding gut bacteria. Yellow bananas are sweeter, easier to digest and just as nutritious. Both are healthy.

How many calories are in a green banana?

About the same as a yellow one: roughly 105 calories in a medium banana (about 118 g). The difference is that more of a green banana's carbs are resistant starch, which your body doesn't fully absorb.

Why do green bananas taste bitter?

Unripe bananas are high in tannins, which make them taste bitter and leave your mouth feeling dry. As the banana ripens, tannins drop and starch turns into sugar, so it gets sweeter.

Do green bananas help you lose weight?

They can help a little because they're filling and low in sugar, so you may eat less. But they don't burn fat, and weight loss still depends on your overall diet and activity.

Can people with diabetes eat green bananas?

Usually yes, and they're often a better choice than ripe bananas because they raise blood sugar more slowly. They still contain carbs, so count them as part of your meal and check your readings.

Do green bananas cause gas?

They can, especially if you eat a lot suddenly. Resistant starch is fermented by gut bacteria, which makes gas. Start with a small amount and increase it over a couple of weeks.

This article is for general information and is not medical advice. Talk to your doctor before changing your diet or taking supplements.