Bananas are one of the best sources of dietary potassium. A large banana provides 487 mg of this mineral, according to the U.S. Department of Agriculture National Nutrient Database. Because your daily requirement for potassium is 4,700 mg, you could exceed this limit by consuming fewer than 10 large bananas in a single day. However, potassium poisoning from eating bananas is unlikely if you are in good health. Consult a dietitian or your health care provider with concerns about your potassium intake.
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Bananas give your diet energy-rich starch and sugars, a very small amount of protein and almost no fat. Although the predominant mineral in bananas is potassium, the fruit also contains low levels of magnesium, zinc and iron. In addition, bananas supply vitamins C and B-6. Only a few food sources offer more potassium to your nutrition plan than bananas, and these include potatoes, prunes and prune juice, raisins, lima beans and acorn squash.
Potassium serves as an electrolyte, a charged ion that helps to provide the electrical signals that your cells need to function. Potassium is a positively-charged ion that resides in high concentrations inside your cells. It works in concert with sodium ions located outside your cells to create an electrochemical gradient between the interior and exterior of the cell membrane. This so-called membrane potential helps to power your cells for muscle contraction, nerve transmission and maintaining your heartbeat. Potassium also functions as a cofactor for enzymes, such as those involved in carbohydrate metabolism. Although potassium toxicity from eating bananas is unlikely, certain medical conditions may lead to dangerously high serum levels if you consume excess potassium.
Hyperkalemia is a condition in which your blood contains elevated levels of potassium. It results from taking in more potassium than your kidneys can excrete, and might be due to kidney disease, overuse of diuretics or a hormone imbalance that affects your kidneys. Symptoms include muscle weakness, tingling of your extremities, temporary paralysis and, in severe cases, an irregular heartbeat that can lead to heart attack. The Linus Pauling Institute of Oregon State University advises there is no established safe upper limit for potassium intake; however, they report an oral dose of at least 18 g results in hyperkalemia in healthy adults. This dose is the equivalent of consuming 37 large bananas at once, making it improbable that you could eat enough bananas to induce toxicity.
Potassium supplements, even if they do not lead to hyperkalemia, may cause gastrointestinal distress, with symptoms including abdominal pain, vomiting and diarrhea. Taking supplements with meals may mitigate these problems. However, fresh foods such as bananas and potatoes supply sufficient dietary potassium to render supplements unnecessary.