The recommendation from the National Cholesterol Education Program states that a cholesterol-reducing diet should contain less than 7% of calories from saturated fat and less than 200 mg of dietary cholesterol per day. What exactly does this mean? For a 2000-calorie diet, 7% corresponds to about 15 grams (about one tablespoon) of saturated fat, but to make sense of this information, you need to know the difference between "saturated", "monounsaturated", and "polyunsaturated" fatty acids. This is explained in the section on fats.
Saturated Fats are not only Animal Fats
Many people equate saturated fats with animal fats, but this is not correct. The fatty acid composition of lard (pork fat) is very similar to human depot fat around the waist and hips. Lard consists of approximately 42% saturated and 58% unsaturated fatty acids. Coconut oil, by contrast, consists of 83% saturated fatty acids. So, lard is better than coconut oil as far as saturation is concerned. However, lard contains 12 mg of cholesterol per tablespoon because it is an animal product, whereas coconut oil has no cholesterol because it is a plant product. Nevertheless, coconut oil will increase cholesterol twice as much as lard because it has double the amount of saturated fat. The comparison of the fatty acid profiles of many edible fats can be found in the chemical description of triglycerides. Saturated fats, whether from vegetable or animal sources, increase cholesterol.
Avoid Hydrogenated Fats
Hydrogenated fats and partially hydrogenated fats affect the body like saturated fats. Partially hydrogenated fats, in particular, contain dietary trans fats that raise the level of low-density lipoproteins (LDL or "bad cholesterol") increasing the risk of coronary heart disease. Trans fats also reduce high-density lipoproteins (HDL or "good cholesterol"), and raise levels of triglycerides in the blood. Both of these conditions are associated with insulin resistance which is linked to diabetes, hypertension, and cardiovascular disease. Harvard University researchers have reported that people who ate partially hydrogenated oils, which are high in Trans fats, had nearly twice the risk of heart attacks compared with those who did not consume hydrogenated oils. Avoid any products with hydrogenated and partially hydrogenated fats. Learn to read labels carefully. Some of your favorite foods may have hydrogenated fats that increase your cholesterol.
Balancing Fatty Acids
The recommendation by government agencies and by the American Heart Association to reduce saturated fat and to increase polyunsaturated fat is based on research that describes how blood cholesterol is affected by fats. In 1965, Hegsted published the results of experiments on the quantitative effects of fatty acids on blood serum cholesterol. The experiments showed that of all the fatty acids in food, only three affected the cholesterol level significantly. Myristic acid (C14:0) increased cholesterol strongly, and palmitic acid (C16:0) also increased cholesterol. Some saturated fatty acids, such as stearic acid (C18:0), had relatively little effect on blood cholesterol. Polyunsaturated fatty acids, such as linoleic acid (C18:2), decreased cholesterol. Dietary cholesterol also increased blood cholesterol. The response of the human body to dietary fats is so consistent that Hegsted was able to derive the following mathematical equation:
Where ΔTC is the change in serum cholesterol in mg/dL. ΔC14:0, ΔC16:0, and ΔPoly are the changes in %kcal.
ΔDietaryCholesterol is in mg/1000 kcal.
Mensink and Katan developed a similar equation based on a detailed analysis of published research:
Where the ΔTC is the change in serum cholesterol values in mg/dL, ΔS is change in percentage of energy from lauric, myristic, and palmitic fatty acids, ΔM is change in energy from monounsaturated fatty acids, and ΔP is change in energy from polyunsaturated fatty acids.
The chart above shows the effects of individual dietary fatty acids on Total Serum Cholesterol, LDL cholesterol, and HDL cholesterol when 1% of the energy from carbohydrates in the diet is replaced by 1% of energy of the specific fatty acids. The chart shows cholesterol increases from lauric acid (C12:0), myristic acid (C14:0), and palmitic acid (C16:0) which are found in coconut oil, palm oil, and butter. Elaidic acid (trans-C18:1), which is present in hydrogenated fats, is the worst because it increases LDL and decreases HDL. The saturated fatty acid stearic acid (C18:0), the monounsaturated oleic acid (C18:1), and the polyunsaturated linoleic acid (C18:2) decrease LDL and increase HDL to various degrees.
These equations and the chart tell us that blood cholesterol can be lowered by avoiding hydrogenated fats, decreasing carbohydrates, and increasing the consumption of polyunsaturated fatty acids such as linoleic acid (C18:2) and alpha-linolenic acid (C18:3) while reducing our consumption of saturated fatty acids like myristic (C14:0) and palmitic (C16:0) acids. Furthermore, the equations make it possible to calculate the effect of various diets or oils on blood cholesterol levels. For example, one tablespoon of butter raises cholesterol as much as 3 tablespoons of lard. Whereas one tablespoon of grape seed oil lowers cholesterol to the same extent that 2 tablespoons of lard increases it. Olive oil does not lower cholesterol significantly because it consists mainly of monounsaturated fat. Polyunsaturated fats are more effective at lowering cholesterol. (See details for various fats). A good diet strategy would be to trim the fat from meats, and accompany the entrees with salads containing salad dressing made with grape seed oil. Safflower oil and sunflower oil can be substituted for the grape seed oil, but only if they are not the "high oleic" variety. Make sure that the quantity of polyunsaturated fat in the label is at least 3 times greater than the monounsaturated fat, as illustrated here:
Carbohydrates are normally metabolized for energy or stored as glycogen in the muscles, but excess carbohydrates are converted to fat, mainly the saturated palmitic acid (C16:0). The metabolic process is known as de novo synthesis of fatty acids and it involves the conversion of glucose to pyruvate, and then to fatty acids through acetyl coenzyme-A (acetyl CoA).
Omega-3 and Omega-6 fatty acids
People on low-fat diets or with plenty of "healthy" monounsaturated fats from olive oil and avocados are sometimes surprised that their cholesterol level is high even though they consume enough fiber and limit their sources of saturated fats and dietary cholesterol. In these cases, cholesterol levels are elevated because the diet does not have polyunsaturated fats to balance the cholesterolemic effect of the palmitic acid created from carbohydrates. Adding sources of polyunsaturated fats to the diet like sunflower seeds, walnuts, or grape seed oil and reducing excessive use of saturated and monounsaturated fats provides the fatty acid balance necessary to normalize cholesterol. Linoleic acid (C18:2), an omega-6 essential fatty acid, and alpha-linolenic acid (C18:3), an omega-3 essential fatty acid, must be included in the diet because the human metabolism cannot create them from other fatty acids.
Mensink and Katan developed equations that calculate the changes in serum lipid and lipoprotein levels caused by isocaloric exchanges of carbohydrates and fatty acids.
The changes (Δ) are in milligrams per deciliter. Expressions in parentheses denote the percentage of daily energy intake from carbohydrates that is replaced by saturated (sat), cis-monounsaturated (mono), or polyunsaturated (poly) fatty acids.
These equations tell us that triglycerides (TG) can be reduced, and HDL can be increased, by reducing carbohydrates in the diet while increasing fats by an equal number of Calories. However, LDL can only be lowered by decreasing the amount of saturated fat relative to the mono- and polyunsaturated fat. The most favorable lipoprotein risk profile for coronary heart disease can be achieved if saturated fatty acids are replaced by unsaturated fatty acids, with no decrease in total fat intake.
Alcohol consumption raises HDL
The observation that moderate alcohol intake is associated with lower atherosclerosis risk gave rise to the term "French Paradox", which refers to the fact that the French suffer a lower incidence of coronary heart disease than Americans, despite consuming relatively more saturated fats. Research suggests that moderate drinkers are less likely to suffer heart attacks than abstainers or heavy drinkers. Alcohol consumption raises HDL cholesterol levels by increasing the transport rate of apolipoproteins A-I and A-II. The equivalent of one shot glass of vodka per day increased HDL cholesterol concentration by 18% compared with the control, and the amount of alcohol consumed correlated with the degree of increase in HDL.
Choosing your foods to reduce LDL
Although your overall cholesterol can be lowered by adding polyunsaturated fats to your diet and decreasing carbohydrates, it is possible for your Total Cholesterol to be normal while your LDL is elevated. Examination of the equation for the change in LDL shows how this can be remedied:
Basically, LDL increases by a factor of 1.28 for every increase in saturated fat, while it decreases by factors of 0.24 and 0.55 for equal increases in monounsaturated fat and polyunsaturated fat, respectively. This means that LDL can be lowered by reducing the dietary saturated fats and replacing them with polyunsaturated and monounsaturated fats. The following table shows the content of saturated fat in various meat and dairy products. The beef and chicken are assumed to be broiled. Fish and skinless chicken breast are your best choices. The fish with the highest levels of omega-3 fatty acids are: mackerel, lake trout, herring, sardines, albacore tuna and salmon.
|Beef||T-bone trimmed to 1/8" fat||486||13.3|
|T-bone trimmed to 0" fat||336||5.6|
|Top Sirloin trimmed to 0" fat||319||4.2|
|Fish||White tuna packed in water||217||1.3|
|Dairy||1 pat of butter||36||2.6|
|1 cup whole milk||146||4.6|
Effect of Fiber
Bile is a digestive liquid produced by the liver consisting of bile acids, cholesterol, phospholipids, and bilirubin. Bile is stored in the gallbladder and then released into the small intestine (the duodenum) to emulsify fats. The primary bile acids are chenodeoxycholic acid (45%) and cholic acid (31%). These bile acids are converted by intestinal bacteria to the secondary bile acids deoxycholate and lithocholate. Both primary and secondary bile acids are reabsorbed by the intestines and delivered back to the liver through the blood stream.
Fiber in the diet can lower blood cholesterol by binding with the components of the bile and preventing their reabsorption. Only soluble fiber has been shown to help lower blood cholesterol when regularly eaten as part of a diet low in saturated fat and cholesterol. Foods high in soluble fiber include oat bran, oatmeal, beans, peas, rice bran, barley, mangos, citrus fruits (including the pulp, not just the juice), strawberries and apple pulp. Dietary supplements with psyllium (Metamucil) or guar gum (Benefiber) also contain soluble fiber.
Insoluble fiber does not lower blood cholesterol, but it is important for normal bowel function. Foods high in insoluble fiber include whole-wheat breads, wheat cereals, wheat bran, beets, cabbage, carrots, Brussels sprouts, turnips, cauliflower and apple skin.
One question that always comes up is: "Can I eat eggs?" Sources of dietary cholesterol do increase blood serum cholesterol, so they should be limited to reduce cholesterol. However, egg whites are a good source of protein and have no cholesterol. Only the yolks have cholesterol. The body responds to dietary cholesterol in approximately linear fashion. Each 1 mg/1000 kcal results in an increase of serum cholesterol of about 0.1 mg/dl. This means that eating one whole egg per day, which has approximately 210 mg of cholesterol, would increase serum cholesterol by approximately 8 mg/dl for someone eating 2500 Calories per day.