Well.....
1. Trade barriers: Under the GATT/WTO it's an exception to the trade barrier rule if you can fit it into one of: (a) Article XX exceptions or (b) Sanitary/Phytosanitary exceptions, among a few others.
In the Beef-Hormone case. The UK/EU argued hormone treated beef was a potential health hazard (sanitary/phytosanitary measure) and produced thousands of pages of science. The US said it wasn't, but could not release studies because they were Monsanto's trade secrets. The US won.
Now, this is once again a burden-of-proof shell game: The UK, rightfully, wanted proof it was harmless before approving it; the US, wrongly but winningly, argued the UK must prove it bad before erecting any trade barriers.
2. Just wait till you see where this is going, folks: Tyson has already created the GMO headless chicken.
3. Any famine problem, the world over, can be solved by: (1) controlling population growth, and (2) a vegetarian diet (as the scientists can tell you, when a Cow eats grass and then we eat the cow, 90% of the energy found in the grass is lost - not to menion the resources we wasted caging, injecting, treating, transporting, and butchering the cow).