Fats Guide
Once upon a time, we didn’t know anything about fat exceptthat it made foods tastier. We cooked our food in lard orshortening. We spread butter on our breakfast toast and ploppedsour cream on our baked potatoes. Farmers bred their animals toproduce milk with high butterfat content and meat “marbled” withfat because that was what most people wanted to eat.
But ever since word got out that diets high in fat are relatedto heart disease, things have become more complicated. Experts tellus there are several different kinds of fat, some of them worse forus than others. In addition to saturated, monounsaturated andpolyunsaturated fats, there are triglycerides, trans fatty acids,and omega 3 and omega 6 fatty acids.
Most people have learned something about cholesterol, and manyof us have been to the doctor for a blood test to learn ourcholesterol “number.” Now, however, it turns out that there’s morethan one kind of cholesterol, too.
Almost every day there are newspaper reports of new studiesor recommendations about what to eat or what not to eat: Lard isbad, olive oil is good, margarine is better for you than butter–then again, maybe it’s not.
Amid the welter of confusing terms and conflicting details,consumers are often baffled about how to improve their diets. FDA recently issued new regulations that will enable consumersto see clearly on a food product’s label how much and what kind offat the product contains. (See “A Little Lite Reading” in theJune 1993 FDA Consumer.) Understanding the terms used to discussfat is crucial if you want to make sure your diet is withinrecommended guidelines (see accompanying article).
Fats and Fatty Acids Fats are a group of chemical compounds that contain fattyacids. Energy is stored in the body mostly in the form of fat. Fatis needed in the diet to supply essential fatty acids, substancesessential for growth but not produced by the body itself.
There are three main types of fatty acids: saturated,monounsaturated and polyunsaturated. All fatty acids are moleculescomposed mostly of carbon and hydrogen atoms. A saturated fattyacid has the maximum possible number of hydrogen atoms attached toevery carbon atom. It is therefore said to be “saturated” withhydrogen atoms.
Some fatty acids are missing one pair of hydrogen atoms in themiddle of the molecule. This gap is called an “unsaturation” andthe fatty acid is said to be “monounsaturated” because it has onegap. Fatty acids that are missing more than one pair of hydrogenatoms are called “polyunsaturated.”
Saturated fats (which contain saturated fatty acids) aremostly found in foods of animal origin. Monounsaturated andpolyunsaturated fats (which contain monounsaturated andpolyunsaturated fatty acids) are mostly found in foods of plantorigin and some seafoods. Polyunsaturated fatty acids are of twokinds, omega-3 or omega-6. Scientists tell them apart by where inthe molecule the “unsaturations,” or missing hydrogen atoms, occur.
Recently a new term has been added to the fat lexicon: transfatty acids. These are byproducts of partial hydrogenation, aprocess in which some of the missing hydrogen atoms are put backinto polyunsaturated fats. “Partially hydrogenated vegetable oils,”such as vegetable shortening and margarine, are solid at roomtemperature.
Cholesterol
Cholesterol is sort of a “cousin” of fat. Both fat andcholesterol belong to a larger family of chemical compounds calledlipids. All the cholesterol the body needs is made by the liver. Itis used to build cell membranes and brain and nerve tissues.Cholesterol also helps the body produce steroid hormones needed forbody regulation, including processing food, and bile acids neededfor digestion.
People don’t need to consume dietary cholesterol because thebody can make enough cholesterol for its needs. But the typicalU.S. diet contains substantial amounts of cholesterol, found infoods such as egg yolks, liver, meat, some shellfish, and whole-milk dairy products. Only foods of animal origin containcholesterol.
Cholesterol is transported in the bloodstream in largemolecules of fat and protein called lipoproteins. Cholesterolcarried in low-density lipoproteins is called LDL-cholesterol; mostcholesterol is of this type. Cholesterol carried in high-densitylipoproteins is called HDL-cholesterol. (See “Fat Words.”)
A person’s cholesterol “number” refers to the total amount ofcholesterol in the blood. Cholesterol is measured in milligrams perdeciliter (mg/dl) of blood. (A deciliter is a tenth of a liter.)
Doctors recommend that total blood cholesterol be kept below 200mg/dl. The average level in adults in this country is 205 to 215mg/dl. Studies in the United States and other countries haveconsistently shown that total cholesterol levels above 200 to 220mg/dl are linked with an increased risk of coronary heart disease.(See “Lowering Cholesterol” in the March 1994 FDA Consumer.)
LDL-cholesterol and HDL-cholesterol act differently in thebody. A high level of LDL-cholesterol in the blood increases therisk of fatty deposits forming in the arteries, which in turnincreases the risk of a heart attack. Thus, LDL-cholesterol hasbeen dubbed “bad” cholesterol.
On the other hand, an elevated level of HDL-cholesterol seemsto have a protective effect against heart disease. For this reason,HDL-cholesterol is often called “good” cholesterol.
In 1992, a panel of medical experts convened by the NationalInstitutes of Health (NIH) recommended that individuals should havetheir level of HDL-cholesterol checked along with their totalcholesterol.
According to the National Heart, Lung, and Blood Institute(NHLBI), a component of NIH, a healthy person who is not at highrisk for heart disease and whose total cholesterol level is in thenormal range (around 200 mg/dl) should have an HDL-cholesterollevel of more than 35 mg/dl. NHLBI also says that an LDL-cholesterol level of less than 130 mg/dl is “desirable” to minimizethe risk of heart disease.
Some very recent studies have suggested that LDL-cholesterolis more likely to cause fatty deposits in the arteries if it hasbeen through a chemical change known as oxidation. However, thesefindings are not accepted by all scientists.
The NIH panel also advised that individuals with high totalcholesterol or other risk factors for coronary heart disease shouldhave their triglyceride levels checked along with their HDL-cholesterol levels.
Triglycerides and VLDL Triglyceride is another form in which fat is transportedthrough the blood to the body tissues. Most of the body’s storedfat is in the form of triglycerides. Another lipoprotein–very low-density lipoprotein, or VLDL–has the job of carrying triglyceridesin the blood. NHLBI considers a triglyceride level below 250 mg/dlto be normal.
It is not clear whether high levels of triglycerides aloneincrease an individual’s risk of heart disease. However, they maybe an important clue that someone is at risk of heart disease forother reasons. Many people who have elevated triglycerides alsohave high LDL-cholesterol or low HDL-cholesterol. People withdiabetes or kidney disease–two conditions that increase the riskof heart disease–are also prone to high triglycerides.
Dietary Fat and Cholesterol Levels Many people are confused about the effect of dietary fats oncholesterol levels. At first glance, it seems reasonable to thinkthat eating less cholesterol would reduce a person’s cholesterollevel. In fact, eating less cholesterol has less effect on bloodcholesterol levels than eating less saturated fat. However, somestudies have found that eating cholesterol increases the risk ofheart disease even if it doesn’t increase blood cholesterol levels.
Another misconception is that people can improve theircholesterol numbers by eating “good” cholesterol. In food, allcholesterol is the same. In the blood, whether cholesterol is”good” or “bad” depends on the type of lipoprotein that’s carryingit.
Polyunsaturated and monounsaturated fats do not promote theformation of artery-clogging fatty deposits the way saturated fatsdo. Some studies show that eating foods that contain these fats canreduce levels of LDL-cholesterol in the blood. Polyunsaturatedfats, such as safflower and corn oil, tend to lower both HDL- andLDL-cholesterol. Edible oils rich in monounsaturated fats, such asolive and canola oil, however, tend to lower LDL-cholesterolwithout affecting HDL levels.
How Do We Know Fat’s a Problem? In 1908, scientists first observed that rabbits fed a diet ofmeat, whole milk, and eggs developed fatty deposits on the walls oftheir arteries that constricted the flow of blood. Narrowing of thearteries by these fatty deposits is called atherosclerosis. It is aslowly progressing disease that can begin early in life but notshow symptoms for many years. In 1913, scientists identified thesubstance responsible for the fatty deposits in the rabbits’arteries as cholesterol.
In 1916, Cornelius de Langen, a Dutch physician working inJava, Indonesia, noticed that native Indonesians had much lowerrates of heart disease than Dutch colonists living on the island.He reported this finding to a medical journal, speculating that theIndonesians’ healthy hearts were linked with their low levels ofblood cholesterol.
De Langen also noticed that both blood cholesterol levels andrates of heart disease soared among Indonesians who abandoned theirnative diet of mostly plant foods and ate a typical Dutch dietcontaining a lot of meat and dairy products. This was the firstrecorded suggestion that diet, cholesterol levels, and heartdisease were related in humans. But de Langen’s observations layunnoticed in an obscure medical journal for more than 40 years.
After World War II, medical researchers in Scandinavia noticedthat deaths from heart disease had declined dramatically during thewar, when food was rationed and meat, dairy products, and eggs werescarce. At about the same time, other researchers found that peoplewho suffered heart attacks had higher levels of blood cholesterolthan people who did not have heart attacks.
Since then, a large body of scientific evidence has beengathered linking high blood cholesterol and a diet high in animalfats with an elevated risk of heart attack. In countries where theaverage person’s blood cholesterol level is less than 180 mg/dl,very few people develop atherosclerosis or have heart attacks. Inmany countries where a lot of people have blood cholesterol levelsabove 220 mg/dl, such as the United States, heart disease is theleading cause of death.
High rates of heart disease are commonly found in countrieswhere the diet is heavy with meat and dairy products containing alot of saturated fats. However, high-fat diets and high rates ofheart disease don’t inevitably go hand-in-hand.
Learning from Other Cultures People living on the Greek island of Crete have very low ratesof heart disease even though their diet is high in fat. Most oftheir dietary fat comes from olive oil, a monounsaturated fat thattends to lower levels of “bad” LDL-cholesterol and maintain levelsof “good” HDL-cholesterol.
The Inuit, or Eskimo, people of Alaska and Greenland also arerelatively free of heart disease despite a high-fat, high-cholesterol diet. The staple food in their diet is fish rich inomega-3 polyunsaturated fatty acids.
Some research has shown that omega-3 fatty acids, found infish such as salmon and mackerel as well as in soybean and canolaoil, lower both LDL-cholesterol and triglyceride levels in theblood. Some nutrition experts recommend eating fish once or twice aweek to reduce heart disease risk. However, dietary supplementscontaining concentrated fish oil are not recommended because thereis insufficient evidence that they are beneficial and little isknown about their long-term effects.
Omega-6 polyunsaturated fatty acids have also been found insome studies to reduce both LDL- and HDL-cholesterol levels in theblood. Linoleic acid, an essential nutrient (one that the bodycannot make for itself) and a component of corn, soybean andsafflower oil, is an omega-6 fatty acid.
At one time, many nutrition experts recommended increasingconsumption of monounsaturated and polyunsaturated fats because oftheir cholesterol-lowering effects. Now, however, the advice issimply to reduce dietary intake of all types of fat. (Infants andyoung children, however, should not restrict dietary fat.)
The available information on fats may be voluminous and issometimes confusing. But sorting through the information becomeseasier once you know the terms and some of the history.
The “bottom line” is actually quite simple, according to JohnE. Vanderveen, Ph.D., director of the Office of Plant and DairyFoods and Beverages in FDA’s Center for Food Safety and AppliedNutrition. What we should be doing is removing as much of thesaturated fat from our diet as we can. We need to select foods thatare lower in total fat and especially in saturated fat.” In anutshell, that means eating fewer foods of animal origin, such asmeat and whole-milk dairy products, and more plant foods such asvegetables and grains. n
Eleanor Mayfield is a writer in Silver Spring, Md.Fat Words
Here are brief definitions of the key terms important to anunderstanding of the role of fat in the diet.Cholesterol: A chemical compound manufactured in the body. It isused to build cell membranes and brain and nerve tissues.Cholesterol also helps the body make steroid hormones and bileacids.
Dietary cholesterol: Cholesterol found in animal products that arepart of the human diet. Egg yolks, liver, meat, some shellfish, andwhole-milk dairy products are all sources of dietary cholesterol.Fatty acid: A molecule composed mostly of carbon and hydrogenatoms. Fatty acids are the building blocks of fats.
Fat: A chemical compound containing one or more fatty acids. Fat isone of the three main constituents of food (the others are proteinand carbohydrate). It is also the principal form in which energy isstored in the body.
Hydrogenated fat: A fat that has been chemically altered by theaddition of hydrogen atoms (see trans fatty acid). Vegetable oiland margarine are hydrogenated fats.Lipid: A chemical compound characterized by the fact that it isinsoluble in water. Both fat and cholesterol are members of thelipid family.
Lipoprotein: A chemical compound made of fat and protein.Lipoproteins that have more fat than protein are called low-densitylipoproteins (LDLs). Lipoproteins that have more protein than fatare called high-density lipoproteins (HDLs). Lipoproteins are foundin the blood, where their main function is to carry cholesterol.Monounsaturated fatty acid: A fatty acid that is missing one pairof hydrogen atoms in the middle of the molecule. The gap is calledan “unsaturation.” Monounsaturated fatty acids are found mostly inplant and sea foods.
Monounsaturated fat: A fat made of monounsaturated fatty acids.Olive oil and canola oil are monounsaturated fats. Monounsaturatedfats tend to lower levels of LDL-cholesterol in the blood.Polyunsaturated fatty acid: A fatty acid that is missing more thanone pair of hydrogen atoms. Polyunsaturated fatty acids are mostlyfound in plant and sea foods.
Polyunsaturated fat: A fat made of polyunsaturated fatty acids.Safflower oil and corn oil are polyunsaturated fats.Polyunsaturated fats tend to lower levels of both HDL-cholesteroland LDL-cholesterol in the blood.
Saturated fatty acid: A fatty acid that has the maximum possiblenumber of hydrogen atoms attached to every carbon atom. It is saidto be “saturated” with hydrogen atoms. Saturated fatty acids aremostly found in animal products such as meat and whole milk.Saturated fat: A fat made of saturated fatty acids. Butter and lardare saturated fats. Saturated fats tend to raise levels of LDL-cholesterol (”bad” cholesterol) in the blood. Elevated levels ofLDL-cholesterol are associated with heart disease.
Trans fatty acid: A polyunsaturated fatty acid in which some of themissing hydrogen atoms have been put back in a chemical processcalled hydrogenation. Trans fatty acids are the building blocks ofhydrogenated fats. n –E.M.Government Advice
Dietary guidelines endorsed by the U.S. Department ofAgriculture and the U.S. Department of Health and Human Servicesadvise consumers to:
Reduce total dietary fat intake to 30 percent or less of totalcalories.
Reduce saturated fat intake to less than 10 percent ofcalories.
Reduce cholesterol intake to less than 300 milligrams daily. n.
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