Palmitelaidic acid is a trans fat.

Trans fatty acids are prevalent in most diets because of the widespread use of hydrogenated oils used by manufacturers of margarines, bakery products, and peanut butters.

Palmitelaidic acid is the shorter and less abundant member of the trans fats, because oils used in hydrogenation contain very little of its precursor, palmitoleic acid.

Fat is necessary for cell membranes, nerve coverings, hormone production, vitamin absorption, and more. Most of us get a lot of fat in our diet, but it usually is not the quality fat we should be getting. We need to eat more “good” fats from flax seed, olive, vegetable, and nut oils (omega- 3, 6, and 9 fats respectively) and less saturated oils and trans fats (or hydrogenated oils) contained in processed foods.

Elevations in palmitelaidic and/or total C:18 trans indicate excessive intake of foods containing trans fats.

The trans fatty acids contain one double bond and thus are included in the unsaturated category. Because of the geometry of the trans bond, however, they behave like saturated fats on the one hand, leading to elevated cholesterol levels (13). On the other hand they mimic unsaturated fats that bind to desaturase enzymes and antagonize the normal production of necessary products. The net effect is to raise plasma LDL cholesterol and lower HDL. It is now the consensus among experts in lipid nutrition that foods containing hydrogenated oils are to be avoided.

References:

https://grey.colorado.edu/mediawiki/sites/shortgut/images/6/62/Plasmafattyacids.pdf