Well, I looked but could not find stats on proportion of world food supply by nation. I doubt that I have the necessary research skills for this. (Nimh! Where are you?) I did find something that stated:
Quote:the U.S., Canada, and Australia together contain less than 6% of the world's population, they currently produce about 20% of the global cereal harvest.
National Academy of Sciences of The USA
I believe that it's reasonable to guess that cereal (rice, corn, wheat) is the largest (in quantity volume if not money) category of foodstuffs, and therefore if these 3 countries together are producing only 20% of global production then the USA does not produce 63% of world food. Perhaps in a particular category (eg. soft drinks) that global percentage might be possible.
On a monetary level, I've heard many times that coffee (which would be a food) is the world's second highest commodity after oil. The USA, outside of the relatively small Hawaiian Kona estates, does not produce any coffee, I don't think. So it would appear that the 63% could not be attainable from a cost of goods POV either.
Maybe the 63% is the percentage of food produced within the USA that is exported from the USA.