Few foods land in as many shopping carts as the banana, and it is also one of the most closely mapped in nutrition databases.
A medium banana weighs about 118 grams and delivers a specific bundle of nutrients backed by USDA, American Heart Association and NIH data.
According to USDA FoodData Central, a medium banana provides 422 milligrams of potassium, roughly 3 grams of fiber, about 10 milligrams of vitamin C, some magnesium and around a quarter of the daily value for vitamin B6.
Potassium and blood pressure
Potassium is the nutrient in bananas with the strongest cardiovascular evidence. The American Heart Association says foods high in potassium help control blood pressure by blunting the effects of sodium and by easing tension in blood vessel walls.
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The organization recommends 3,500 to 5,000 milligrams of potassium a day for adults trying to prevent or treat high blood pressure, ideally from food.
A single medium banana covers a modest but meaningful share of that. Pairing it with other potassium-rich foods, like beans, potatoes and leafy greens, is how most people close the gap.
Resistant starch feeds gut bacteria
The gut effect depends on ripeness. Less-ripe, greener bananas contain more resistant starch, a form of carbohydrate that skips digestion in the small intestine and reaches the colon largely intact.
Harvard Health Publishing notes that resistant starch becomes food for beneficial microorganisms in the microbiome. Those bacteria produce butyrate and other short-chain fatty acids, anti-inflammatory compounds that help nourish the cells lining the gut.
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Harvard reports that green bananas contain about a third more resistant starch than yellow ones.
The mood link runs through B6
Bananas are often described as a mood food. The connection is more chemistry than folklore.
Vitamin B6, which a medium banana supplies in meaningful amounts, is a cofactor for the enzyme that converts the amino acid tryptophan into serotonin, a neurotransmitter involved in mood regulation.
The National Institutes of Health describes vitamin B6 as involved in more than 100 enzymatic reactions, including neurotransmitter synthesis.
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Bananas provide both B6 and tryptophan in the same package, though a single fruit will not shift mood on its own. The evidence for direct effects of dietary tryptophan on mood in healthy adults remains limited.
The other nutrients that add up
The vitamin C in a medium banana covers around 11 percent of the daily value and supports normal immune function.
The magnesium contributes to muscle and nerve function, useful for anyone who eats a banana around a workout. The fiber, about 3 grams per fruit, supports regular digestion.
None of this turns bananas into a miracle food. It makes them a well-documented, easy-to-add option in a diet aimed at healthy blood pressure and steady digestion.
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When to check with a doctor first
More is not always better. The AHA cautions that too much potassium can be harmful in older adults and in people with kidney disorders, because aging and impaired kidney function reduce the body's ability to clear it from the blood.
The NIH Office of Dietary Supplements adds that the standard intake targets do not apply to people with impaired potassium excretion, whether from kidney disease or from certain medications.
Anyone in that group who is unsure how much potassium is safe should ask their doctor before increasing banana intake or other high-potassium foods.
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