MadSci Network: General Biology

Re: How long does it take for 'hot dogs' to be fully digested?

Date: Fri Apr 6 16:57:00 2001
Posted By: Phyllis Stumbo, Staff, Nutrition, University of Iowa
Area of science: General Biology
ID: 985813934.Gb

This brings up some interesting issues, but not a definitive answer.  You 
might answer that question several ways. If you define digestion as the 
chemical breakdown of food by enzymes to prepare it for absorption then 
only a few hours are required.  However we usually talk about digestion 
AND absorption as a continuous process.  Your example of 7 years could 
only refer to both digestion and absorption.

If you think about how long the substance of a hot dog resides in the 
intestinal tract before being expelled, we know from studies that food 
passes through the body at different rates for different people, taking 
from around ˝ day to several days.  But this is not digestion.  If 
digestion is the process of breaking down food and absorbing nutrients 
from the food into the body to be carried to cells through the blood and 
lymph systems then much more time is involved.  (This might be referred to 
as digestion, absorption and metabolism.)  

An enterprising young investigator surprised most of us with some very 
clever experiments in the 1950’s.  He demonstrated that amino acids, fats 
and other components of foods are incorporated in most body tissues on a 
daily basis, that the tissues in our muscles and skin and organs exchange 
some of the structural molecules on a continuous basis.  So, it is 
conceivable that a molecule of protein or fat from a hotdog might be 
incorporated into muscle or fat tissue and stay there for a long time.  I 
agree that stating that these molecules would persist for 7 years is 
unlikely, but I would not suggest it is impossible.

Another way you might give a time to “digestion” is to consider the rise 
and fall of blood sugar following a meal.  The blood sugar rises from the 
fasting state and remains elevated for 4 to 6 hours after food is 
consumed.  With this as a guide you might say it takes 6 hours to digest a 
hotdog.  But if you want to count the time that all molecules from your 
food passes through your body and are gone from the body, then your 
estimate would be as good as mine.  This makes the statement “You are what 
you eat” have REAL meaning.

Phyllis Stumbo
University of Iowa

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