|MadSci Network: Medicine|
Thanks for posting such an interesting question. Actually, you are partially correct that the human digestive system can't digest sweet corn (on the cob). The part that you see exit your body as part of your fecal matter is actually the part that the human digestive system can't do much with, because we don't have the enzymes (complicated proteins that the body creates) to break apart what the corn kernel covering is made of...some animals can, though. I think that maybe seeing the coverings not digested is what made you think that the whole corn kernel isn't digested.
The rest of the corn kernel (the interior stuff) is easily digestible by the human digestive system. The center part of the kernel is mainly starch (complex carbohydrate) and a little bit of protein...and a few vitamins and minerals. The human body then can absorb the breakdown products from the starch and protein, as well as the vitamins and minerals into the blood stream, where the materials can be delivered to the rest of the body tissues.
So, the end result is that, in order to get the maxiumum nutritional yield from the sweet corn you eat, make sure that it is well cooked and that you chew it well, so your digestive tract has the chance to 'capture' all the nutrients that it can from the corn.
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