Fats and Cholesterol

 

* Fats and Cholesterol - The Good, The Bad, and The Healthy Diet

"Eat a low-fat, low-cholesterol diet." Most of us have heard this simple recommendation so often over the past two decades that we can recite it in our sleep. Touted as a way to lose weight and prevent cancer and heart disease, it's no wonder much of the nation - and food producers - hopped on board.

 

Unfortunately, this simple message is now largely out of date. Detailed research -much of it done at Harvard - shows that the total amount of fat in the diet, whether high or low, isn't really linked with disease. What really matters is the type of fat in the diet.(1) Bad fats increase the risk for certain diseases and good fats lower the risk. The key is to substitute good fats for bad fats.

 

And cholesterol in food? Although it is still important to limit the amount of cholesterol your eat, especially if you have diabetes, dietary cholesterol isn't nearly the villain it's been portrayed to be. Cholesterol in the bloodstream is what's most important. High blood cholesterol levels greatly increase the risk for heart disease. But the average person makes about 75% of blood cholesterol in his or her liver, while only about 25% is absorbed from food. The biggest influence on blood cholesterol level is the mix of fats in the diet.

 

DIETARY FATS
Type of Fat	Main Source	State at Room Temperature	Effect on Cholesterol Levels
Monounsaturated	Olives; olive oil, canola oil, peanut oil; cashews, almonds, peanuts, and most other nuts; avocados	Liquid	Lowers LDL; raises HDL
Polyunsaturated	Corn, soybean, safflower, and cottonseed oils; fish	Liquid	Lowers LDL; raises HDL
Saturated	Whole milk, butter, cheese, and ice cream; red meat; chocolate; coconuts, coconut milk, and coconut oil	Solid	Raises both LDL and HDL
Trans	Most margarines; vegetable shortening; partially hydrogenated vegetable oil; deep-fried chips; many fast foods; most commercial baked goods	Solid or semi-solid	Raises LDL

 

The Cholesterol--Heart Disease Connection

 

Cholesterol is a wax-like substance. The liver makes it and links it to carrier proteins called lipoproteins that let it dissolve in blood and be transported to all parts of the body. Why? Cholesterol play essential roles in the formation of cell membranes, some hormones, and vitamin D.

 

Too much cholesterol in the blood, though, can lead to problems. In the 1960s and 70s, scientists established a link between high blood cholesterol levels and heart disease. Deposits of cholesterol can build up inside arteries. These deposits, called plaque, can narrow an artery enough to slow or block blood flow. This narrowing process, called atherosclerosis, commonly occurs in arteries that nourish the heart (the coronary arteries). When one or more sections of heart muscle fail to get enough blood, and thus the oxygen and nutrients they need, the result may be the chest pain known as angina. In addition, plaque can rupture, causing blood clots that may lead to heart attack, stroke, or sudden death. Fortunately, the buildup of cholesterol can be slowed, stopped, and even reversed.

 

Cholesterol-carrying lipoproteins play central roles in the development of atherosclerotic plaque and cardiovascular disease. The two main types of lipoproteins basically work in opposite directions.

Low-density lipoproteins (LDL) carry cholesterol from the liver to the rest of the body. When there is too much LDL cholesterol in the blood, it can be deposited on the walls of the coronary arteries. Because of this, LDL cholesterol is often referred to as the "bad" cholesterol.

High-density lipoproteins (HDL) carry cholesterol from the blood back to the liver, which processes the cholesterol for elimination from the body. HDL makes it less likely that excess cholesterol in the blood will be deposited in the coronary arteries, which is why HDL cholesterol is often referred to as the "good" cholesterol.

 

In general, the higher your LDL and the lower your HDL, the greater your risk for atherosclerosis and heart disease.

For adults age 20 years or over, the latest guidelines from the National Cholesterol Education Program recommend the following optimal levels:

- Total cholesterol less than 200 milligrams per deciliter (mg/dl)

- HDL cholesterol levels greater than 40 mg/dl

- LDL cholesterol levels less than 100 mg/dl

 

* Dietary Fat, Dietary Cholesterol, and Blood Cholesterol Levels

One of the most important determinants of blood cholesterol level is fat in the diet - not total fat, as mentioned already, but specific types of fat. Some types of fat are clearly good for cholesterol levels and others are clearly bad for them.

 

 Cholesterol in food

 

While it is well known that high blood cholesterol levels are associated with an increased risk for heart disease, scientific studies have shown that there is only a weak relationship between the amount of cholesterol a person consumes and their blood cholesterol levels or risk for heart disease. For some people with high cholesterol, reducing the amount of cholesterol in the diet has a small but helpful impact on blood cholesterol levels. For others, the amount of cholesterol eaten has little impact on the amount of cholesterol circulating in the blood.

 

In a study of over 80,000 female nurses, Harvard researchers actually found that increasing cholesterol intake by 200 mg for every 1000 calories in the diet (about an egg a day) did not appreciably increase the risk for heart disease.

 

Eggs

 

Long vilified by well-meaning doctors and scientists for their high cholesterol content, eggs are now making a bit of a comeback. Recent research by Harvard investigators has shown that moderate egg consumption--up to one a day--does not increase heart disease risk in healthy individuals.(2) While it's true that egg yolks have a lot of cholesterol--and, therefore may slightly affect blood cholesterol levels--eggs also contain nutrients that may help lower the risk for heart disease, including protein, vitamins B12 and D, riboflavin, and folate.

 

So, when eaten in moderation, eggs can be part of a healthy diet. People with diabetes, though, should probably limit themselves to no more than two or three eggs a week, as the Nurses' Health Study found that for such individuals, an egg a day might increase the risk for heart disease. Similarly, people who have difficulty controlling their blood cholesterol may also want to be cautious about eating egg yolks and choose foods made with egg whites instead.

 

Dietary Fats

 

The Bad Fats

Some fats are bad because they tend to worsen blood cholesterol levels.

Saturated Fats

 

Saturated fats are mainly animal fats. They are found in meat, seafood, whole-milk dairy products (cheese, milk, and ice cream), poultry skin, and egg yolks. Some plant foods are also high in saturated fats, including coconut and coconut oil, palm oil, and palm kernel oil. Saturated fats raise total blood cholesterol levels more than dietary cholesterol because they tend to boost both good HDL and bad LDL cholesterol. The net effect is negative, meaning it's important to limit saturated fats.

 

Trans Fats

 

Trans fatty acids are fats produced by heating liquid vegetable oils in the presence of hydrogen. This process is known as hydrogenation. The more hydrogenated an oil is, the harder it will be at room temperature. For example, a spreadable tub margarine is less hydrogenated and so has fewer trans fats than a stick margarine.

Most of the trans fats in the American diet are found in commercially prepared baked goods, margarines, snack foods, and processed foods. Commercially prepared fried foods, like French fries and onion rings, also contain a good deal of trans fat.

Trans fats are even worse for cholesterol levels than saturated fats because they raise bad LDL and lower good HDL. While you should limit your intake of saturated fats, it is important to eliminate trans fats from partially hydrogenated oils from your diet.

 

The Good Fats

 

Some fats are good because they can improve blood cholesterol levels.

Unsaturated Fats--Polyunsaturated and Monounsaturated

Unsaturated fats are found in products derived from plant sources, such as vegetable oils, nuts, and seeds. There are two main categories: polyunsaturated fats (which are found in high concentrations in sunflower, corn, and soybean oils) and monounsaturated fats (which are found in high concentrations in canola, peanut, and olive oils). In studies in which polyunsaturated and monounsaturated fats were eaten in place of carbohydrates, these good fats decreased LDL levels and increased HDL levels.

 

Percentage of Specific Types of Fat in Common Oils and Fats*
Oils	Saturated	Mono-unsaturated	Poly-unsaturated	Trans
Canola	7	58	29	0
Safflower	9	12	74	0
Sunflower	10	20	66	0
Corn	13	24	60	0
Olive	13	72	8	0
Soybean	16	44	37	0
Peanut	17	49	32	0
Palm	50	37	10	0
Coconut	87	6	2	0
Cooking Fats
Shortening	22	29	29	18
Lard	39	44	11	1
Butter	60	26	5	5
Margarine/Spreads
70% Soybean Oil, Stick	18	2	29	23
67% Corn & Soybean Oil Spread, Tub	16	27	44	11
48% Soybean Oil Spread, Tub	17	24	49	8
60% Sunflower, Soybean, and Canola Oil Spread, Tub	18	22	54	5
*Values expressed as percent of total fat; data are from analyses at Harvard School of Public Health Lipid Laboratory and U.S.D.A. publications.