Growing up, my parents were very strict about sugar intake, because they had heard "somewhere" that eating refined sugar lowered your immune system function for 12-24 hours.
At the time, this seemed to be anecdotally true to me, because as a kid if I did actually eat something with a lot of sugar (candy, dessert) I would often have a sore throat or stuffy nose the next day.
This article from WebMD seems to support this, but doesn't cite any references:
Eating or drinking too much sugar curbs immune system cells that attack bacteria. This effect lasts for at least a few hours after downing a couple of sugary drinks.
Are there any large studies that show this link? What is the current medical consensus on whether sugar intake makes you more susceptible to infection?