A study at Nanjing University in China found that ingested "microRNA" (very small pieces of ribonucleic acid, or RNA) from plants were able to survive digestion and influence the function of human cells.
Food columnist Ari Levaux has a piece digging into the implications, in The Atlantic. The basic idea: if this research stands up to the rigors of scientific scrutiny, it could prove that when we eat food, we consume not just fuel and nutrients, but information that changes us on a cellular level, and influences health.
Monsanto's website states, "There is no need for, or value in testing the safety of GM foods in humans." This viewpoint, while good for business, is built on an understanding of genetics circa 1950. It follows what's called the "Central Dogma" (PDF) of genetics, which postulates a one-way chain of command between DNA and the cells DNA governs.
The Central Dogma resembles the process of ordering a pizza. The DNA knows what kind of pizza it wants, and orders it. The RNA is the order slip, which communicates the specifics of the pizza to the cook. The finished and delivered pizza is analogous to the protein that DNA codes for.
We've known for years that the Central Dogma, though basically correct, is overly simplistic. For example: Pieces of microRNA that don't code for anything, pizza or otherwise, can travel among cells and influence their activities in many other ways. So while the DNA is ordering pizza, it's also bombarding the pizzeria with unrelated RNA messages that can cancel a cheese delivery, pay the dishwasher nine million dollars, or email the secret sauce recipe to WikiLeaks.
Monsanto's claim that human toxicology tests are unwarranted is based on the doctrine of "substantial equivalence." This term is used around the world as the basis of regulations designed to facilitate the rapid commercialization of genetically engineered foods, by sparing them from extensive safety testing.
via The Very Real Danger of Genetically Modified Foods - The Atlantic. You'll also want to read the actual study, and make up your own mind.