I also think you're mischaracterizing HDL as a VLDL. If you search for Apolipoprotein A here: https://www.ncbi.nlm.nih.gov/books/NBK305896/ you'll see that HDL is constructed from it, while VLDL and LDL are part of the Apolipoprotein B lineage.
1. When someone consumes fat, bile is released into the gut.
2. Oatmeal (and other soluble fibers like psyllium husk) capture this bile and it is excreted in stool.
3. In order to create the bile, the liver needs LDL. Because the LDL it used to create the bile was lost when it was captured, it exposes more LDL receptors and pulls LDL out of the bloodstream, thereby lowering LDL levels.
It seems to me that in order to maximize the effectiveness of this LDL-lowering approach, one must not simply consume psyllium or oatmeal, but rather consume them in conjunction with fat. Not saturated fat, obviously, which raises LDL, but perhaps unsaturated or polyunsaturated fats. My expectation is that this would trigger the bile secretion required in order to actually sequester it.
I don't think that's correct: https://en.wikipedia.org/wiki/Enterohepatic_circulation
I also think you're mischaracterizing HDL as a VLDL. If you search for Apolipoprotein A here: https://www.ncbi.nlm.nih.gov/books/NBK305896/ you'll see that HDL is constructed from it, while VLDL and LDL are part of the Apolipoprotein B lineage.