GM Food and Health

On Reason's Hit & Run blog, Katherine Mangu-Ward writes:

America has been chowing down on modified corn and soybeans for years now to no ill effect.

I know everyone says this, and I guess I more or less believe it too, but really, has anyone ever proven this? Are there scientific studies that show no consequences from eating GM foods? Even one? It'd be a difficult study -- you're have to account for a lot of different factors, and GM foods have only been around for ~7-10 years.

I'd just like to know if there is indeed any scientific evidence for Mangu-Ward's claim.