Eating can cause low blood pressure, from the Harvard Heart Letter
If you sometimes feel dizzy or lightheaded after eating a meal, you could have a common condition called postprandial hypotension, meaning low blood pressure after eating, reports the July 2010 issue of the Harvard Heart Letter.
Digestion is a complicated job that requires coordination between the digestive, nervous, and circulatory systems. To compensate for blood going to the stomach and small intestine during digestion, the heart beats faster while blood vessels narrow. When the heart and blood vessels don't respond as they should, blood pressure drops.