Why no food before cardiolite stress test?

[egg1]

I have been instructed not to consume caffeine 24 hours prior to my cardiolite stress test, and to fast the morning of the test.
I understand that caffeine affects the heart, and so will avoid caffeine even though it means a headache.
It is very difficult for me to fast. Although I am healthy, I am used to eating something every 2-3 hours. When I do not, I feel lightheaded and weak and miserable, and cannot imagine getting on a treadmill. Breakfast would not interfere with hard exercise (I always eat breakfast before my morning workout). Is there a medical reason to avoid food, or is it just for comfort while exercising?

[Flycaster305]

Do you have a diabetes?  Your symptoms sound exactly how I feel if my blood sugar drops too low.  I'm allowed to control my insulin before stress tests.

[Douglas Bogart, MD]

It is important not to eat as the test may make you nauseated and you will be less likely to vomit if you haven't eaten.  Also the gut uptake of the isotope is less if you haven't eaten.