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Name: Daphna
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: Saturday, June 01, 2002


Question:
My friend says your stomach absorbs 80% of the nutrients of a meal within 20 minutes of the food being there. I say that is incorrect. Do you know how long it takes for the food to be absorbed in your stomach and what percent of it is absorbed before moving to the small intestine for further absorption?


Replies:
Generally very little of any of the food we eat will be absorbed through the gastric mucosa, except things like alcohol which can in part make its way through. Fats, oils proteins and carbohydrates will be almost totally be absorbed in the small intestine after further emulsification and digestion upon entering the duodenum.

Peter Faletra Ph.D.
Assistant Director
Science Education
Office of Science
Department of Energy


I believe you are correct. How fast a substance is absorbed and where it is absorbed in the digestive tract depends on: what the food substance is, what other foods are consumed with it, individual differences, what medications one might be using, and a host of other considerations. Water and ethanol are rapidly consumed, even in the mouth and esophagus to some extent, and are absorbed almost completely in the stomach. Fats, which require bile need to pass the gall bladder ducts (if you have a gall bladder) or the liver in order to be digested. This occurs in the small intestine. Complex carbohydrates require a long time to break down into simple sugars, such as glucose. That is why long distance runners load up with carbohydrates several hours before a race, not just 20 minutes. That would make them very nauseated. In addition, their digestion requires insulin that empties from the pancreas in the small intestine.

Finally, if your friend's timing were true, anorexia nervosa / bulimia nervosa would not be the life-threatening conditions that they are.

Vince Calder


First of all, most nutrients are absorbed into the small intestine, not the stomach. The job of the stomach is to add hydrochloric acid and some peptidases, which are enzymes that help break down protein into smaller chunks. Even then, most protein digestion takes place in the small intestine. The stomach also churns your food into a mush called chyme, which passes slowly, bit by bit, into the small intestine through the pyloric sphincter muscle. You have amylases in your saliva which begin the breakdown of carbohydrates, but those too are mostly digested in the small intestine. So I would say your friend is mistaken. vanhoeck


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