Same food at every stage; the carbohydrate just changes form. Green, most of its energy is resistant starch that walks past your small intestine and feeds gut microbes; ripe, that starch has turned to sugar. Potassium, fibre, and B6 hold steady throughout.

Blood pressure is the strongest line, and it's really about potassium. A medium banana carries about 422 mg ¹. Push daily intake into the 3.5 to 4.7 g range and systolic pressure drops about 3.5 mm Hg in normal adults, roughly 7 in hypertensives, with a quarter lower stroke risk at the higher band ². The average U.S. adult eats about 2,500 mg ³, so a banana closes a real slice.

The ripeness lever shows up in the glycaemic numbers. A ripe banana is GI 51, an underripe one GI 30, a boiled green plantain GI 39 ⁴. Green-banana starch improves glucose tolerance across a 22-study review ⁵, and brought weight loss and better insulin sensitivity in type-2 diabetics ⁶.

Gut and legs round it out. Two bananas a day for 30 days raised faecal Bifidobacterium ⁷, and a banana matched a 6% sports drink over a 75 km time trial on time and power, with better recovery markers ^{8 9}.

Buy green-tipped and eat across the arc, rather than racing ripe fruit against the clock.

Weeks: a home cuff reads a few points lower if you were low on potassium, on the order of a small ACE-inhibitor dose ¹⁰. A month or two: faecal bifidobacteria climb ⁷, and hour-long sessions cost nothing to fuel. Years: a high-fibre, high-resistant-starch pattern pulls 15 to 30% off all-cause and cardiovascular mortality ¹¹. Bananas are one line on that pattern: a cheap habit that moves five things a little.