there are multiple mechanisms and theres not a scholarly consensus. We discuss evidence and mechanisms in the book. Some reasons an excess of omega-6 is obesogenic include:
- it generates a dysbiotic gut flora and increases the risk of metabolic endotoxemia (an influx of endotoxins into the body), which causes metabolic syndrome;
- omega-6 fats are largely rejected by cells that have little use for them, and this means they accumulate in adipose tissue, because they have no place else to go;
- they suppress omega-3 lengthening and disturb membrane fatty acid profiles with inflammatory effects
this can promote macrophage and adipocyte activation which causes adipose tissue to hold onto fat
it can also suppress or distort immune function increasing the risk of infections which may promote obesity;
- it leads to higher levels of lipid peroxidation in mitochondria, damaging the mitochondria and impairing their ability to dispose of an energy excess;
- omega-6 fats are intrinsically less able to generate ROS (reactive oxygen species) in mitochondria, which limits the ability of mitochondria to regulate energy influx and increases vulnerability to mitochondrial dysfunction;
- omega-6 fats are precursors to endocannibinoids which increase appetite (see this article).
The relative importance of different mechanisms is not known; different mechanisms may be operative in different people. However, that dietary omega-6 fat consumption is highly correlated with adipose tissue omega-6 concentration and with general obesity seems very clear at this point.