When you eat saturated and trans fats, cholesterol is deposited in the arteries. When you eat too much of these fats, high deposits of fatty substances and cholesterol in the arteries (among other things) cause a plaque to form and the arteries to harden and narrow; artherosclerosis is the medical term that describes this hardening and narrowing of the arteries. (Athero is Greek for paste; sclerosis means hardness). Eventually, the build up of plaque can get large enough to actually restrict blood flow through the artery, or it can rupture and cause a clot to form. This clot then travels to other parts of the body.

A plaque-blocked artery, or a clot in the artery, affects the organ to which the artery is connected. In both cases the organ that is supplied by the artery is starved of blood and oxygen and the organ’s cells may die or suffer severe damage. If the organ is the heart, the blockage or clot can cause a heart attack (coronary thrombosis); if the organ is the brain, the blockage or clot can cause a stroke. If blood supply to the arms or legs is restricted, it can cause difficulty with movement, and, eventually, gangrene.

The good news is that unsaturated fats, or “good” fats, can have the opposite effect by improving blood cholesterol levels, lowering platelet stickiness (platelets are the cells in the blood involved with the process of clotting) and reducing the adhesion of plaque to the artery walls.

Saturated fats further restrict blood flow through the arteries because they stiffen red blood cell membranes and increase blood viscosity (thickness). Stiff red blood cells are inflexible and can’t easily navigate their way down the arteries. They can also pile up to form what look like coin stacks, called rouleaux. In narrow blood vessels this makes blood flow and oxygen release even more difficult.  

But again, the good news is that unsaturated fats improve blood flow by reducing blood viscosity and increasing the flexibility of red blood cells. Flexible blood cells can turn and twist themselves more easily and thereby squeeze through tiny artery capillaries which are often half their diameter.