A recent study demonstrates that palmitic acid (PA), the most common fatty saturated acid found in animals, plants, and microorganisms) promotes intestinal IgA responses. They demonstrate that PA directly enhances these responses and also enhances these responses through sphingolipid metabolism. Though the authors suggest that PA might be useful in mucosal vaccines, intestinal IgA responses, particularly secretory IgA (sIgA) responses, are an important part of intestinal homeostasis. The authors found that dietary PA increased intestinal IgA (sIgA) but not circulating IgA.
Notably, elevated intestinal IgA (in the lamina propria, not sIgA) is associated with increased circulating IgA, which might drive systemic immune responses to mucosal antigens (ref: PMI, 2013) though circulating IgA has also been demonstrated to have immunomodulatory effects.
As pointed out in the paper, PA is also a ligand for TLR4 and TLR2, however signaling through TLR in the intestine is an important part of intestinal epithelial cell development, function, and homeostasis. In health, TLR4 is usually “barely detectable” and tends to be upregulated in states of inflammation (such as Crohn’s disease and colitis).
According to the authors,
“Therefore, like bacterial products, PA has the opposite immunologic effect on intestinal and systemic immune compartments and actually plays a beneficial role in the maturation of the intestinal immune system.”
Note that the “baseline” diet of the animals used in the study was as follows, and it is unclear whether a different baseline diet with the addition of PA would have yielded the same results:
“Chemically defined AIN-93M–based diets containing soybean, palm, or coconut oil or soybean oil plus supplemental purified PA were from Oriental Yeast”
Palmitic acid is found at high levels in plam oil. Mark Sisson has promoted palm oil because of it’s antioxidant capacity (and has a great question post on palmitic acid), but Jeff Leach thinks we should reconsider and Dr. Weil thinks we should avoid it.