Neu5Gc

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In autoimmune disorders the immune system attacks the body's own tissues. We recommend that these tissues be removed because clearly they are causing an immune reaction.

Um...what? It seems funny, but that seems to be the reaction of some scientists to Neu5Gc, a sugar that apes, but not humans, synthesize naturally. However, we do ingest it in food, particularly meat and dairy products.

Some humans have an inflammatory immune reaction to it. Does that mean it's bad to eat? Numerous papers on Neu5Gc that I've read seem to suggest so in their discussion sections.

I was reminded of that when reading this Atlantic article on chimp fertility studies:

Gagneux’s lab space was adjacent to that of his collaborator Ajit Varki, who had helped uncover the functioning of the sugars, known as sialic acids, on cell surfaces. The sialic acids on the surfaces of human and chimp sperm have become the focus of Gagneux’s work, too. Humans, as Varki discovered, have lost the ability to make one sialic acid, Neu5Gc, and Gagneux suspected that Neu5Gc played a role in fertilization. He hypothesized that Neu5Gc helped female chimpanzees, in a process called “cryptic female choice,” get the benefit of the most-compatible, highest-quality sperm. The sugar acted like the fuzzy part of Velcro and attached to barbs formed by sugar-binding proteins on the surface of the cells in the uterus or fallopian tubes. Neu5Gc, as Gagneux imagined it, might “sweet-talk” the female reproductive system.

Gagneux’s Neu5Gc ideas had a critical implication for human fertility. Although we have lost the ability to synthesize Neu5Gc, we ingest the sugar when we eat meat and dairy products, and it, in turn, can then be incorporated into our cells. Does Neu5Gc coat the surface of human sperm? Is it found more readily on the sperm of men who eat lots of animal products? Does the extremely foreign Neu5Gc then trigger in women an immune response that selects against the survival of the sperm? “It could be that men who eat loads of meat pass a threshold and become infertile,” suggested Gagneux. [emphasis mine]

This just cries out for better general education of scientists. Does her hypothesis make sense? Inuit and Nenet cultures eat almost all-meat. Shouldn't they have died out by then?

Maybe instead of pegging this sugar as the bad guy, we should wonder why we are reacting to it in the first place? Unfortunately all the populations that they have studied for a reaction have been western. Most people do seem to have a reaction to Neu5Gc, but this paper has a tantalizing graph:

See the humans clustered around the chimps? Who are they? Why the difference? 

Dr. Ayers at Cooling Inflammation suggests the reaction might be due to too little dietary NeufGc:

If cow’s milk gangliosides are the source of Neu5Gc in breastmilk, then how do the infants develop antibodies to these relatively rare antigens? Babies receive all of their antibodies from their mother until their immune systems start to develop at about six months of age. The answer is hinted at by the observation of a mother whose exclusively breastfed infant developed sensitivity to breast milk after the mother ate dairy products. The mother reported that she shifted from a long term vegan diet to a meat diet to improve her nutrition during her pregnancy. It is also likely that she produced IgE antibodies to Neu5Gc, which were then transferred to her baby across the placenta during gestation.

 

I would also suspect that increased gut permeability due to the constant irritation from foods like gluten, poor gut microflora populations, and general inflammation play a role.