"If you then examined the European national youth teams that feed the World Cup and professional ranks, you would find this strange phenomenon to be even more pronounced."
closed as off-topic by Jim, user140086, choster, Nathaniel, Brian Hooper Dec 10 '15 at 13:04
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Feed in this context means "provide".
So the youth teams provide players for the European leagues.
"The high schools in our area are of a high level, and feed directly into the Ivy League Universities."
Meaning that the Ivy League Universities take many students from the high schools in our area.