Defining fatty acids and their relationship to dietary fat

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Fatty acids are the building blocks of fats. Chemically speaking, a fatty acid is a chain of carbon atoms with hydrogen atoms attached and a carbon-oxygen-oxygen-hydrogen group (the unit that makes it an acid) at one end.

All the fats in food are combinations of fatty acids. Nutritionists characterize fatty acids as saturated, monounsaturated, or polyunsaturated, depending on how many hydrogen atoms are attached to the carbon atoms in the chain. The more hydrogen atoms, the more saturated the fatty acid. Depending on which fatty acids predominate, a food fat is likewise characterized as saturated, monounsaturated, or polyunsaturated.

1 A saturated fat, such as butter, has mostly saturated fatty acids. Saturated fats are solid at room temperature and get harder when chilled.

1 A monounsaturated fat, such as olive oil, has mostly monounsaturated fatty acids. Monounsaturated fats are liquid at room temperature; they get thicker when chilled.

1 A polyunsaturated fat, such as corn oil, has mostly polyunsaturated fatty acids. Polyunsaturated fats are liquid at room temperature; they stay liquid when chilled.

So why is margarine, which is made from unsaturated fats such as corn and soybean oil, a solid? Because it's been artificially saturated by food chemists who add hydrogen atoms to some of its unsaturated fatty acids. This process, known as hydrogenation, turns an oil, such as corn oil, into a solid fat that can be used in products such as margarines without leaking out all over the table. A fatty acid with extra hydrogen atoms is called a hydro-genated fatty acid. Another name for hydrogenated fatty acid is trans fatty acid. Trans fatty acids are not healthy for your heart. Because of those darned extra hydrogen atoms, they are, well, more saturated, and they act like — what else? — saturated fats, clogging arteries and raising the levels of cholesterol in your blood. To make it easier for you to control your trans fat intake, the Food and Drug Administration now requires a new line on the Nutritional Facts label that tells you exactly how many grams of trans fats are in any product you buy.

In the meantime, as I explain in Controlling Cholesterol For Dummies (a whole doggone book — published by Wiley — on how to whip your cholesterol profile into shape), the same smart food chemists who invented hydrogenation have now come up with trans fat-free margarines and spreads, including some that are made with plant sterols and stanols.

Plant sterols are natural compounds found in oils in grains, fruits, and vegetables, including soybeans, while stanols are compounds created by adding hydrogen atoms to sterols from wood pulp and other plant sources. Sterols and stanols work like little sponges, sopping up cholesterol in your intestines before it can make its way into your bloodstream. As a result, your total cholesterol levels and your levels of low-density lipoproteins (otherwise known as LDLs or "bad cholesterol") go down. In some studies, one to two 1-tablespoon servings a day of sterols and stanols can lower levels of bad cholesterol by 10 to 17 percent, with results showing up in as little as two weeks. Wow!

A nutritional fish story

When Sir William Gilbert, lyricist to songsmith Sir Arthur Sullivan, wrote, "Here's a pretty kettle of fish!" he may well have been talking about the latest skinny on seafood.

The good news from a 2002 Harvard survey of more than 43,000 male health professionals shows that the ones who eat 3 to 5 ounces of fish just once a month have a 40 percent lower risk of ischemic stroke, a stroke caused by a blood clot in a cranial artery. The Harvard study did not include women, but a report on women and stroke published in the Journal of the American MedicalAssociation in 2000 says that women who eat about 4 ounces of fish — think one small can of tuna — two to four times a week appear to cut their risk of stroke by a similar 40 percent.

These benefits are, in large part, because of the presence of omega-3 fatty acids, which are unsaturated fatty acids found most commonly in fatty fish such as salmon and sardines. The primary omega-3 is alpha-linolenic acid, which your body converts to hormonelike substances called eicosanoids. The eicosanoids— eicosapentaenoic acid (EPA) and docosa-hexaenoic acid (DHA) — reduce inflammation, perhaps by inhibiting an enzyme called COX-2, which is linked to inflammatory diseases such as rheumatoid arthritis (RA). The Arthritis Foundation says omega-3s relieve RA joint inflammation, swelling, and pain.

Omega-3s also are heart-friendly. The fats make the tiny blood particles called platelets less sticky, reducing the possibility that they'll clump together to form blood clots that might obstruct a blood vessel and trigger a heart attack. Omega-3s also knock down levels of bad cholesterol so effectively that the American Heart Association recommends eating fish at least twice a week. Besides, fish also is a good source of taurine, an amino acid the journal Circulation notes helps maintain the elasticity of blood vessels, which means that the vessels may dilate to permit blood or — horrors! — a blot clot to flow through.

Did I mention that omega-3s are bone builders? Fish oils enable your body to create calciferol, a naturally occurring form of vitamin D, the nutrient that enables your body to absorb bone-building calcium — which may be why omega-3s appear to help hold minerals in bone — and increase the formation of new bone.

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88 Part II: What You Get from Food

(continued)

A pretty kettle of fish, indeed.

You can find respectable amounts of omega-

A pretty kettle of fish, indeed.

You can find respectable amounts of omega-

3s in

Anchovies

Tuna (albacore)

Haddock

Broccoli

Herring

Kale

Mackerel

Spinach

Salmon

Canola oil

Sardines

Walnut oil

Scallops

Flaxseed oil

Consumer Alert No. 1

Consumer Alert No. 1

Before you shout, "Waiter! Bring me the salmon, mackerel, herring, or whatever," here's the other side of the coin. Earlier research suggests that frequent servings of fish may increase the risk of a stroke caused by bleeding in the brain. This situation is common among Native Alaskans who eat plenty of fish and have a higher than normal incidence of hemorrhagic, or bleeding, strokes. True, the Harvard study found no significant link between fish consumption and bleeding strokes, but researchers say more studies are needed to nail down the relationship — or lack thereof.

Consumer Alert No. 2

Not all omegas are equally beneficial. Omega-6 fatty acids — polyunsaturated fats found in beef, pork, and several vegetable oils, including corn, sunflower, cottonseed, soybean, peanut, and sesame oils — are chemical cousins of omega-3s, but the omega-6s lack the benefits of the omega-3s.

Consumer Alert No. 3

Wait! Don't go just yet. Despite all the benefits fish bring to a healthful diet, my technical editor, University of Maine Food Science Professor Alfred Bushway, wants me to remind you that some fish, particularly those caught in the wild (rather than raised on a fish farm), may be contaminated with metals such as mercury, which has made its way into the water as industrial pollution and may be hazardous for women who are or may be pregnant. Check the food bulletins in your local newspaper or check the FDA's hotline (listed on its Web site, which you can find in Chapter 27) for the most up-to-date data.

Now it's really a pretty kettle of fish!

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Table 7-1 shows the kinds of fatty acids found in some common dietary fats and oils. Fats are characterized according to their predominant fatty acids. For example, as you can plainly see in the table, nearly 25 percent of the fatty acids in corn oil are monounsaturated fatty acids. Nevertheless, because corn oil has more polyunsaturated fatty acid, corn oil is considered a polyun-saturated fatty acid. Note for math majors: Some of the totals in Table 7-1 don't add up to 100 percent because these fats and oils also contain other kinds of fatty acids in amounts so small that they don't affect the basic character of the fat.

Exploring the chemical structure of fatty acids

If you don't have a clue about the chemical structure of fatty acids, reading this explanation may be worth your while. The concepts are simple, and the information you find here applies to all kinds of molecules, not just fatty acids.

Moleculesare groups of atoms hooked together by chemical bonds. Different atoms form different numbers of bonds with other atoms. For example, a hydrogen atom can form one bond with one other atom; an oxygen atom can form two bonds with other atoms; and a carbon atom can form four bonds to other atoms.

To actually see how this works, visualize a carbon atom as one of those round pieces in a child's Erector set or Tinkertoy kit. Your carbon atom (C) has — figuratively speaking, of course — four holes: one on top, one on the bottom, and one on each side. If you stick a peg into each hole and attach a small piece of wood representing a hydrogen atom (H) to the pegs on the top, the bottom, and the left, you have a structure that looks like this:

The preceding molecule is a saturated fatty acid because it has a hydrogen atom at every available carbon link in the chain. A monoun-saturated fatty acid drops two hydrogen atoms and forms one double bond (two lines instead of one) between two carbon atoms. A polyunsaturated fatty acid drops more hydrogen atoms and forms several (poly) double bonds between several carbon atoms. Every hydrogen atom still forms one bond, and every carbon atom still forms four bonds, but they do so in a slightly different way. These sketches are not pictures of real fatty acids, which have many more carbons in the chain and have their double bonds in different places, but they can give you an idea of what fatty acids look like up close.

This unit, called a methyl group, is the first piece in any fatty acid. To build the rest of the fatty acid, you add carbon atoms and hydrogen atoms to form a chain. At the end, you tack on a group with one carbon atom, two oxygen atoms, and a hydrogen atom. This group is called an acid group, the part that makes the chain of carbon and hydrogen atoms a fatty acid.

90 part ||: what You Get from Food

Table 7-1

What Fatty Acids Are in That Fat or Oil?

Fat or Oil

Saturated Fatty Monounsaturated Polyunsaturated Kind of Fat Acid (%) Fatty Acid (%) Fatty Acid (%) or Oil

Canola oil

7

53

22

Monounsaturated

Corn oil

13

24

59

Polyunsaturated

Olive oil

14

74

9

Mono-unsaturated

Palm oil

52

38

10

Saturated

Peanut oil

17

46

32

Mono-unsaturated

Safflower oil

9

12

74

Polyunsaturated

Soybean oil

15

23

51

Polyunsaturated

Soybean-cottonseed oil

18

29

48

Polyunsaturated

Butter

62

30

5

Saturated

Lard

39

45

11

Saturated*

  • Because more than one-third of its fats are saturated, nutritionists label lard a saturated fat. Nutritive Value of Foods (Washington, D.C.: U.S. Department of Agriculture); Food and Life (New York American Council on Science and Health)
  • Because more than one-third of its fats are saturated, nutritionists label lard a saturated fat. Nutritive Value of Foods (Washington, D.C.: U.S. Department of Agriculture); Food and Life (New York American Council on Science and Health)

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