Re: Why is it said to wait 1 hour after eating before going swimming?

Aloha, Bobby,

     First, let me apologize for taking such a time to post an answer to 
your question.  I was hoping to talk with one of my colleagues who is our 
resident sports nutrition expert here at the University of Hawai`i (Human 
Nutrition, Food, and Animal Sciences Department).  However, Dr. Alan 
Titchenal has been home ill with the flu for the past week...he just 
returned to work yesterday, and I had a chance to check out my proposed 
answer with him this morning.  While I am a human nutritionist by 
training, I usually trust Dr. Titchenal's judgment, better, on matters 
such as your question.

     Anyway,I had part of the answer right.  Actually, the recommendation 
to wait an hour after swimming probably should be applied to most forms of 
physical exercise/exertion.  When you eat and the food gets into the 
stomach and then into the small intestine (where most of the work of 
digestion and absorption takes place), the body 'pulls' extra blood into 
the body's middle (around the internal organs), so that the nutrients can 
then be transferred into the blood and sent to the rest of the body.  
Since you have a fixed amount of blood in your body, the amount of the 
blood that is left in the outer muscles must then be less.  So, you have 
less blood in the large muscles that you need for exercise...and that 
increases the chances for muscle cramping (due to the production of by-
products, such as lactic acid, which are toxic to the muscles).

     Dr. Titchenal also mentioned that maybe where the 'old wive's tale' 
about waiting for swimming, in particular, originated because when you are 
swimming you are usually face-down.  This might make you more prone to 
getting sick to your stomach and throwing up, because of the stomach being 
full and your face is in the water.  I wonder if anyone ever tested this 
after eating by swimming face down and then swimming on his/her back?
 
     So, bottom line:  it may be a good idea not to exercise for about an 
hour after eating (particularly a big meal), regardless of the exercise.