Artery-clogging fats. That's one of the phrases one reads in the news media almost every day. It conjures up an image of arteries clogged just like your plumbing gets clogged when you pour grease down the drain.
But fats in the bloodstream are not at all the same as grease in your plumbing.
Your plumbing gets clogged because fats that were liquid when they were hot become solid when they hit the cool pipes. Different fats become solid at different temperatures (called their melting points), depending on how saturated they are. The more saturated a fat, the higher the temperature at which it becomes solid.
Lamb fat is one of the most saturated fats. That's why it sometimes becomes solid on your plate in cool weather. Pork fat is more than half unsaturated. Chicken fat is much more unsaturated, and it's almost liquid on hot summer days.
We call fats that are liquid at normal room temperatures oils. Olive oil is a liquid at normal room temperature, but it can partially solidify when you put it into the refrigerator.
This explains why fats can solidify on our plates, or in our plumbing. But our blood is not kept at room temperature. It's kept several degrees above normal body temperature of about 98.6 degrees Farenheit, well above the melting point of even the most saturated fats.
Furthermore, fats don't just float around in the bloodstream by themselves. Blood is mostly water, and fat is insoluble in water. So special proteins in the blood transport fats from here to there in the body. That's one of the function of the lipoproteins that we call chylomicrons, LDL, HDL, VLDL, and so forth. Fatty acids, the building blocks of fat, are transported in the blood bound by a common blood protein, albumin.
In other words, fats do not clog our arteries like fats clog our plumbing, by solidifying when the temperature gets too low. Fats are good sources of energy and are good for storing energy for future use. Some fatty acids are used as signalling molecules. Hence our bodies (unlike our plumbing) have evolved ways to transport these useful fats to the cells that need them. Chylomicrons ferry dietary fats to the liver. VLDL ferries fat from the liver to the cells that need them, and HDL brings unused fats back to the liver.
Now, fats could "clog" our arteries by other mechanisms, by somehow triggering the formation of plaque, which can gradually reduce the internal diameter of our blood vessels. But the relation between dietary fat and atherosclerosis (the name we give to arteries that are clogged with plaque) is controversial, some people saying it's excess dietary fat that is the problem and others saying it's excess dietary carbohydrate, especially rapidly digested processed carbohyrdrate.
Or perhaps inflammation is the main culprit. Or damage to the arteries by other factors, like long-term high blood pressure.
Whatever turns out to be the main cause of plaque, and ultimately compromised blood flow, it's not melted fat solidifying in our arteries.