Excellent summary, posted below: https://www.reddit.com/r/science/comments/2qr4t9/sugar_molecule_links_red_meat_consumption_and/cn8vbu6
First, Varki is a behemoth in the emerging field of glycobiology. His research is usually top notch.
Secondly, he has some very interesting theories on evolution and the role that sugars might have played in our brain development. Outside of DNA, sialic acids (NeuNAc) have been called the most interesting molecules in all of biology. Near the same exact time millions of years ago when our ancestors evolutionary diverged from chimpanzees, we developed a mutation in an enzyme known as CMAH. CMAH catalyzes the addition of a hydroxyl group to sialic acid (NeuNAc) to produce Neu5Gc (NeuNAc w/ added -OH). One of the things that makes you uniquely human compared to almost all other mammals are the patterns of carbohydrates that cover the surface of your cells, and in particular, what makes you uniquely human is the striking lack of Neu5Gc on your cells compared to almost all other mammals. Sialic acids are heavily present in the brain, and are quite abundant on the surfaces of neurons; we now know that sialic acids have very profound roles in neuronal plasticity, memory, learning, and brain development after fertilization. The fact that humans were no longer able to synthesize hydroxylated forms of sialic acid (Neu5Gc) could have, in theory, had a radical effect on the way our brains evolved (according to Varki) because of the fundamental role that sialic acids have in modeling our brain during development and for memory/learning.
Sialic acids decorate the surfaces of all cells. As mentioned, all mammals besides humans have Neu5Gc on their cells. When you consume meat, Neu5Gc from your foods get stripped from the cells that comprise the meat you consumed and can be metabolically incorporated onto the surface of your cells. Glycobiology and your immune system has evolved in tandem over millions of years, and the fact that Neu5Gc isn’t human means it gets recognized by the immune system which in theory could lead to the results linked by the OP.