Bananas change composition dramatically as they ripen. Green, they are largely starch, much of it resistant starch that resists digestion. As they yellow, that starch breaks down into sugars.
Same fruit, different glycaemic response, different effect on the gut. "Is banana good?" is less useful than "which stage of banana?"
Key benefits
Potassium supports blood pressure
About 400 mg in a medium banana. Potassium helps excrete sodium and lowers vascular tension, which matters most in a diet already high in salt.
Green banana resistant starch feeds the gut
Resistant starch escapes absorption in the small intestine and reaches the colon, where it feeds beneficial bacteria and supports production of short-chain fatty acids like butyrate. Ripening reduces it.
It is rich in vitamin B6
One banana covers around 25% of an adult's daily requirement. Vitamin B6 is needed for amino acid metabolism and neurotransmitter synthesis.
A practical fuel around exercise
A ripe banana digests quickly and delivers sugars and potassium together. Trials found it matched sports drinks as a carbohydrate source during exercise.
How to eat it well
- Pick underripe if blood sugar is the concern, ripe if you want quick energy.
- Pair it with nuts or yoghurt to flatten the glucose response.
- Frozen banana works well in smoothies and loses almost nothing nutritionally.
- Black spots on the peel mean peak sweetness and minimum resistant starch.
- Refrigeration blackens the skin but slows ripening of the flesh.
What to watch out for
- If you restrict potassium for chronic kidney disease, portion carefully.
- There is sugar here, so if you manage blood glucose, settling on about one a day is sensible.
- Latex allergy can produce a cross-reaction.
- In migraine-prone people, tyramine is occasionally a trigger.
Nutrition
Approximate values per 100 g edible portion.
- Calories
- 89 kcal
- Carbohydrates
- 22.8 g
- Fiber
- 2.6 g
- Sugars
- 12.2 g
- Protein
- 1.1 g
- Potassium
- 358 mg
- Vitamin B6
- 0.37 mg
- Vitamin C
- 8.7 mg
- Magnesium
- 27 mg
Key nutrients
- Potassium
- Vitamin B6
- Vitamin C
- Magnesium
- Fiber