How does food cholesterol impact the development of heart disease?
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One of the earliest recommendations for reducing blood cholesterol levels was to follow a low cholesterol diet. However, it soon became apparent that blood cholesterol levels are influenced more by how much saturated fat is eaten rather than cholesterol. Cholesterol is derived from animal foods; as a general rule, animal foods that are higher in saturated fat usually contain cholesterol. Focusing on reducing the level of saturated fat in the diet usually results in a reduction in diet cholesterol as well. |
About 500 to 1000 milligrams of cholesterol is made in the body daily, with the liver producing the most. What’s more, the level of production in the liver can be affected by diet levels, meaning as diet consumption goes up production go down and vice versa. Thus, the negative impact of eating more cholesterol may not be as significant as we think. For instance, the impact of eating a diet containing 400 milligrams versus 300 milligrams of cholesterol daily results in an increase of only a couple of milligrams of total blood cholesterol.
How does saturated fat influence risk factors for heart disease?
Eating a diet higher in saturated fat seems to increase total and LDL-cholesterol levels. Most, but not all saturated fatty acids seem to have the ability to raise blood cholesterol levels. These saturated fatty acids may impact blood cholesterol levels by slowing the mechanisms that remove circulating LDL from the blood and potentially increasing production of cholesterol in the liver. As a result, there is a general increase in LDL and total cholesterol levels.
How can saturated fatty acids slow the removal of cholesterol from the blood?
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The types of fatty acids eaten will be reflected by the fatty acid composition in the plasma membranes (phospholipid fatty acids). When more of the fatty acids are saturated, and thus fairly straight, neighboring molecules can get closer making the membrane more crowded and less dynamic (fluid). When LDL receptors surface on the plasma membrane, they actually must migrate to anchoring sites (see LDL Receptor Cycling Figure). Once they are anchored they can then bind circulating LDLs and bring it into that cell. The LDL is then broken down and the cholesterol is available to that cell. Meanwhile the receptor is then able to resurface on the plasma membrane and migrate to the anchoring site. This process is often called LDL receptor cycling and the rate-limiting step is the LDL receptor migration from its surfacing site to its anchoring site. Therefore if the migration takes longer, the whole cycle takes longer and less LDL is removed from the blood throughout the day. |
How do unsaturated fatty acids affect cholesterol levels?
Regarding unsaturated fatty acids, neither monounsaturated fatty acids (MUFAs) nor polyunsaturated fatty acids (PUFAs) have a cholesterol-elevating impact. In fact, if they are used to replace saturated fatty acids in the diet, total cholesterol will probably be lowered. This is especially true for people whose blood cholesterol levels were elevated well above recommended levels. This is one reason why populations that consuming higher fat intakes, with less of the fat via saturated fat sources enjoy lower rates of heart disease.
