Fibers
A high proportion of starch in unripe bananas is resistant starch, which, as the name suggests, is resistant to digestion and is therefore a type of fiber.
Resistant starch passes down to the large intestine where it is fermented by bacteria in a process that forms butyrate, a short-chain fatty acid that appears to have beneficial effects on intestinal health (4).
Bananas are also a good source of other types of fiber, such as pectin. Some of the pectin in bananas is water-soluble.
When bananas ripen, the proportion of water-soluble pectin increases, which is one of the main reasons why bananas turn softer as they age (5).
Both pectin and resistant starch moderate the rise in blood sugar after a meal.
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Potassium in bananas
Ø Maintaining Normal Blood Pressure
Diets high in potassium are associated with improved blood pressure control. There are several mechanisms contributing to this beneficial effect, including improved kidney function, reduction in blood clotting, and more efficient opening of blood vessels. Because of these important benefits, therapeutic diets aimed at improving blood pressure control often place primary focus on increasing potassium from foods.
Ø In addition, diets rich in potassium have been associated with a reduction in kidney stone risk. This is thought to be because the naturally occurring potassium salts in plant foods help to neutralize acidity in the blood stream. This prevents leeching of calcium from the bones to buffer the acid, which in turn reduces urine calcium, preventing its deposition in the form of a stone.