Are Bananas Very High in Potassium?*
©Copyright 2008 by Robert Chuckrow
When asked what foods are very high in potassium, most people say, “bananas.” According to Composition of Foods (Agriculture Handbook No. 8),* for a 100 gram, edible portion:
Item 141 Raw banana: 370 mg of potassium.
Many other common foods have potassium content as high or higher than bananas. For example:
Item 368 Cooked hamburger: 558 mg of potassium.
(100 grams is about equal to 3-1/2 ounces, so 5-1/4 oz of banana has about the same amount of potassium as 3-1/2 oz of cooked hamburger.)
So why are bananas reputed to be extremely high in potassium? Here’s my guess:
Someone may have been looking up the potassium content of various foods and found that dehydrated bananas are very high in potassium. A 100-g portion of bananas contains 75 g of water, so when the water is removed, 25 g of solid matter remains. Now, a 100-g portion of dried bananas will have 100 g of solid matter—four times as much as raw bananas. Therefore, the quantities of all of the nutrients are multiplied by a factor of four (100/25). Thus a 100-g portion of dried bananas would be expected to contain about 4(370) = 1,480 mg of potassium. Actually, dehydrated bananas contain a small percentage of water, so a 100-g portion of dried bananas has slightly less potassium than 1480 mg. According to Agriculture Handbook No. 8:
Item 143 Dehydrated banana (banana powder): 1,477 mg of potassium.
Similarly, the potassium content of a 100-g portion of dried beef would have a correspondingly higher potassium content than non-dehydrated beef:
Item 380 Uncooked dried Beef: 4,300 mg of potassium.
When the nutrient content of two foods are compared, both should be in the same form—both as commonly eaten or both on a dry basis. A similar error resulted in the misconception that beans are high in protein.
*Published by Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402, 1963.
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