Unripe tropical fruits such as banana, papaya and mango contain digestive-resistant starch1 — indigestible low-viscous fibers that slowly ferment in your large intestine. These resistant starches feed healthy bacteria, essentially acting as prebiotics.
They also bulk up your bowel movements for easier, timelier disposal without making you feel bloated or gassy. Best of all, they don't spike your blood sugar the way completely ripened fruit and other starchy foods do, so they actually help improve rather than worsen insulin regulation.2,3 In many ways, resistant starch could be considered a third type of fiber (in addition to soluble and insoluble fiber).
Unripe fruits aren't the only foods with this ability, however. Researchers have discovered even high net-carb foods such as potatoes,4rice, bread and pasta become more digestive-resistant when prepared in certain ways.