The chemical family name for fats and related compounds such as cholesterol is lipids (from lipos, the Greek word for fat). Liquid fats are called oils; solid fats are called, well, fat.

With the exception of cholesterol (a fatty substance that has no calories and provides no energy), fats are high-energy nutrients.

Gram for gram, fats have more than twice as much energy potential (calories) as protein and carbohydrates (affectionately referred to as carbs): 9 calories per fat gram versus 4 calories per gram for proteins and carbs.

In this article, I cut the fat away from the subject of fats and zero in on the essential facts you need to put together a diet with just enough fat (yes, you do need fat) to provide the bounce that every diet requires. And then I deal with that ultimate baddie — cholesterol. Surprise! You need some of that, too. Onward.

Finding the Facts about Fat Stuff

Fats are sources of energy that add flavor to food — the sizzle on the steak, you can say. However, as anyone who’s spent the last 30 years on planet Earth knows, fats may also be hazardous to your health. The trick is separating the good from the bad. Trust me. It can be done. And this section explains how.

Understanding how your body uses fat

Here’s a sentence that you probably never thought you’d read: A healthy body needs fat. Your body uses dietary fat (the fat that you get from food) to make tissue and manufacture biochemicals, such as hormones. Some of the body fat made from food fat is visible.

Even though your skin covers it, you can see the fat in the adipose (fatty) tissue in female breasts, hips, thighs, buttocks, and belly or male abdomen and shoulders. This visible body fat:

• Provides a source of stored energy

• Gives shape to your body

• Cushions your skin

• Acts as an insulation blanket that reduces heat loss

Other body fat is invisible. You can’t see this body fat because it’s tucked away in and around your internal organs. This hidden fat is:

• Part of every cell membrane (the outer skin that holds each cell together)

• A component of myelin, the fatty material that sheathes nerve cells and makes it possible for them to fire the electrical messages that enable you to think, see, speak, move, and perform the multitude of tasks natural to a living body; brain tissue also is rich in fat

• A shock absorber that protects your organs (as much as possible) if you fall or are injured

• A constituent of hormones and other biochemicals, such as vitamin D and bile

Pulling energy from fat

Although fat has more energy (calories) per gram than proteins and carbohydrates, your body has a more difficult time pulling the energy out of fatty foods. Imagine a chain of long balloons — the kind people twist into shapes that resemble dachshunds, flowers, and other amusing things.

When you drop one of these balloons into water, it floats. That’s exactly what happens when you swallow fat-rich foods. The fat floats on top of the watery food-and-liquid mixture in your stomach, which limits the effect that lipases — fat-busting digestive enzymes in the mix below — can have on it.

Because fat is digested more slowly than proteins and carbohydrates, you feel fuller (a condition called satiety) longer after eating high-fat food.

Into the intestines

When the fat moves down your digestive tract into your small intestine, an intestinal hormone called cholestokinin beeps your gallbladder, signaling for the release of bile. Bile is an emulsifier, a substance that enables fat to mix with water so that lipases can start breaking the fat into glycerol and fatty acids.

These smaller fragments may be stored in special cells (fat cells) in adipose tissue, or they may be absorbed into cells in the intestinal wall, where one of the following happens:

• They’re combined with oxygen (or burned) to produce heat/energy, water, and the waste product carbon dioxide.
• They’re used to make lipoproteins that haul fats, including cholesterol, through your bloodstream.

Into the body

Glucose, the molecule you get by digesting carbohydrates, is the body’s basic source of energy. Burning glucose is easier and more efficient than burning fat, so your body always goes for carbohydrates first.

But if you’ve used up all your available glucose — maybe you’re stranded in a cabin in the Arctic, you haven’t eaten for a week, a blizzard’s howling outside, and the corner deli 500 miles down the road doesn’t deliver — then it’s time to start in on your body fat.

The first step is for an enzyme in your fat cells to break up stored triglycerides (the form of fat in adipose tissue). The enzyme action releases glycerol and fatty acids, which travel through your blood to body cells, where they combine with oxygen to produce heat/energy, plus water — lots of water — and the waste product carbon dioxide.

As anyone who has used a highprotein/ high-fat/low-carb weight-loss diet such as the Atkins regimen can tell you, in addition to all that water, burning fat without glucose produces a second waste product called ketones.

In extreme cases, high concentrations of ketones (a condition known as ketosis) alter the acid/alkaline balance (or pH) of your blood and may trip you into a coma. Left untreated, ketosis can lead to death.

Medically, this condition is most common among people with diabetes. For people on a low-carb diet, the more likely sign of ketosis is stinky urine or breath that smells like acetone (nail polish remover).

Focusing on the fats in food

Food contains three kinds of fats: triglycerides, phospholipids, and sterols. Here’s how they differ:

• Triglycerides: You use these fats to make adipose tissue and burn for energy.

• Phospholipids: Phospholipids are hybrids — part lipid, part phosphate (a molecule made with the mineral phosphorus) — that act as tiny rowboats, ferrying hormones and fat-soluble vitamins A, D, E, and K through your blood and back and forth in the watery fluid that flows across cell membranes. (By the way, the official name for fluid around cells is extracellular fluid. See why I just called it watery fluid?)

• Sterols (steroid alcohols): These are fat and alcohol compounds with no calories. Vitamin D is a sterol. So is the sex hormone testosterone. And so is cholesterol, the base on which your body builds hormones and vitamins.

Getting the right amount of fat

Getting the right amount of fat in your diet is a delicate balancing act. Too much, and you increase your risk of obesity, diabetes, heart disease, and some forms of cancer. (The risk of colon cancer seems to be tied more clearly to a diet high in fat from meat rather than fat from dairy products.)

Too little fat, and infants don’t thrive, children don’t grow, and everyone, regardless of age, is unable to absorb and use fat-soluble vitamins that smooth the skin, protect vision, bolster the immune system, and keep reproductive organs functioning.

In the fall of 2002, the National Academies’ Institute of Medicine (IOM) recommended that no more than 20 to 45 percent of daily calories should come from fat. On a 2,000-calorie daily diet, that’s 400 to 900 calories from fats a day. The Dietary Guidelines for Americans 2005 lowers that to 20 to 30 percent of total calories.

Translation: 400 to 600 of the calories on a 2,000-calorie/day regimen. Because your body doesn’t need to get saturated fats, cholesterol, or trans fats from food, neither IOM nor the Dietary Guidelines for Americans 2005 have set levels for these nutrients, except to say, “Keep them as low as possible, please.” This advice about fat intake is primarily for adults.

Although many organizations, such as the American Academy of Pediatrics, the American Heart Association, and the National Heart, Lung, and Blood Institute, recommend restricting fat intake for older children, they stress that infants and toddlers require fatty acids for proper physical growth and mental development, and that’s why Mother Nature made human breast milk so high in fatty acids. Never limit the fat in your baby’s diet without checking first with your pediatrician.

Essential fatty acids

An essential fatty acid is one that your body needs but cannot assemble from other fats. You have to get it whole, from food. Linoleic acid, found in vegetable oils, is an essential fatty acid. Two others — linolenic acid and arachidonic acid — occupy a somewhat ambiguous position.

You can’t make them from scratch, but you can make them if you have enough linoleic acid on hand, so food scientists can work up a good fight about whether linolenic and arachidonic acids are actually “essential.” In practical terms, who cares?

Linoleic acid is so widely available in food, you’re unlikely to experience a deficiency of any of the three — linoleic, linolenic, or arachidonic acids — as long as 2 percent of the calories you get each day come from fat.

In 2002, the Institute of Medicine (IOM) published the first daily recommendations for two essential fatty acids, alpha-linolenic acid and linolenic acid.

The former is an omega-3 fatty acid that’s found in fish oils, milk, and some veggie oils. The latter is an omega-6 fatty acid (ditto), found in safflower and corn oil. IOM recommends that:

• Women get 12 grams linolenic acid and 1.1 grams alpha-linolenic acid per day
• Men get 17 grams linolenic acid and 1.6 grams alpha-linolenic acid per day

Finding fat in all kinds of foods

As a general rule:

• Fruits and vegetables have only traces of fat, primarily unsaturated fatty acids.

• Grains have small amounts of fat, up to 3 percent of their total weight.

• Dairy products vary. Cream is a high-fat food. Regular milks and cheeses are moderately high in fat. Skim milk and skim milk products are low-fat foods. Most of the fat in any dairy product is saturated fatty acids.

• Meat is moderately high in fat, and most of its fats are saturated fatty acids.

• Poultry (chicken and turkey), without the skin, is relatively low in fat.

• Fish may be high or low in fat, primarily unsaturated fatty acids that — lucky for the fish — remain liquid even when the fish is swimming in cold water. (Saturated fats harden when cooled.)

• Vegetable oils, butter, and lard are high-fat foods. Most of the fatty acids in vegetable oils are unsaturated; most of the fatty acids in lard and butter are saturated.

• Processed foods, such as cakes, breads, canned or frozen meat, and vegetable dishes, are generally higher in fat than plain grains, meats, fruits, and vegetables.

Here’s a simple guide to finding which foods are high (or low) in fat. Oils are virtually 100 percent fat. Butter and lard are close behind.

After that, the fat level drops, from 70 percent for some nuts down to 2 percent for most bread. The rule to take away from these numbers? A diet high in grains and plants always is lower in fat than a diet high in meat and oils.

Defining fatty acids and their relationship to dietary fat

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-oxygenoxygen- 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.

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

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

• 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 hydrogenated 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, 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!

Table 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 polyunsaturated fatty acid. Note for math majors: Some of the totals in Table 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.

Fat or Oil	Saturated Fatty Acid (%)	Monounsaturated Fatty Acid (%)	Polyunsaturated Fatty Acid (%)	Kind of Fat or Oil
Canola oil	7	53	22	Monounsaturated
Corn oil	13	24	59	Polyunsaturated
Olive oil	14	74	9	Monounsaturated
Palm oil	52	38	10	Saturated
Peanut oil	17	46	32	Monounsaturated
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)

Considering Cholesterol and You

I mention earlier in this article that your body actually needs fat, and here’s another sentence that may blow your (nutritional) mind: Every healthy body needs cholesterol. Look carefully and you find cholesterol in and around your cells, in your fatty tissue, in your organs, and in your glands.

What’s it doing there? Plenty of useful things. For example, cholesterol

• Protects the integrity of cell membranes

• Helps enable nerve cells to send messages back and forth

• Is a building block for vitamin D (a sterol), made when sunlight hits the fat just under your skin

• Enables your gallbladder to make bile acids, digestive chemicals that, in turn, enable you to absorb fats and fat-soluble nutrients such as vitamin A, vitamin D, vitamin E, and vitamin K

• Is a base on which you build steroid hormones such as estrogen and testosterone

Cholesterol and heart disease

Doctors measure your cholesterol level by taking a sample of blood and counting the milligrams of cholesterol in 1 deciliter (1⁄10 liter) of blood. When you get your annual report from the doctor, your total cholesterol level looks something like this: 225 mg/dl.

Translation: You have 225 milligrams of cholesterol in every tenth of a liter of blood. Why does this matter? Because cholesterol makes its way into blood vessels, sticks to the walls, and forms deposits that eventually block the flow of blood.

The more cholesterol you have floating in your blood, the more cholesterol is likely to cross into your arteries, where it may increase your risk of heart attack or stroke.

As a general rule, the National Cholesterol Education Program (NCEP) says that for adults, a cholesterol level higher than 250 mg/dl is a high risk factor for heart disease; between 200 mg/dl and 250 mg/dl is considered a moderate risk factor; below 200 mg/dl is considered a low risk factor. Cholesterol levels alone are not the entire story.

Many people with high cholesterol levels live to a ripe old age, but others with low total cholesterol levels develop heart disease. Worse yet, recent research indicates that low cholesterol levels may increase the risk of stroke.

In other words, cholesterol is only one of several risk factors for heart disease. Here are some more:

• An unfavorable ratio of lipoproteins
• Smoking
• Obesity
• Age (being older is riskier)
• Sex (being male is riskier)
• A family history of heart disease

To estimate your own risk of heart disease/heart attack, check out the NCEP heart attack risk calculator.

Living with lipoproteins

A lipoprotein is a fat (lipo = fat, remember?) and protein particle that carries cholesterol through your blood. Your body makes four types of lipoproteins: chylomicrons, very low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs).

As a general rule, LDLs take cholesterol into blood vessels; HDLs carry it out of the body. A lipoprotein is born as a chylomicron, made in your intestinal cells from protein and triglycerides (fats). After 12 hours of traveling through your blood and around your body, a chylomicron has lost virtually all of its fats.

By the time the chylomicron makes its way to your liver, the only thing left is protein. The liver, a veritable fat and cholesterol factory, collects fatty acid fragments from your blood and uses them to make cholesterol and new fatty acids.

Time out! How much cholesterol you get from food may affect your liver’s daily output: Eat more cholesterol, and your liver may make less. If you eat less cholesterol, your liver may make more. And so it goes.

Churning out harmful lipoproteins

Okay, after your liver has made cholesterol and fatty acids, it packages them with protein as very low-density lipoproteins (VLDLs), which have more protein and are denser than their precursors, the chylomicrons. As VLDLs travel through your bloodstream, they lose triglycerides, pick up cholesterol, and turn into low-density lipoproteins (LDLs).

LDLs supply cholesterol to your body cells, which use it to make new cell membranes and manufacture sterol compounds such as hormones. That’s the good news. The bad news is that both VLDLs and LDLs are soft and squishy enough to pass through blood vessel walls.

The larger and squishier they are, the more likely they are to slide into your arteries, which means that VLDLs are more hazardous to your health than plain old LDLs. These fluffy, fatty lipoproteins carry cholesterol into blood vessels, where it can cling to the inside wall, forming deposits, or plaques.

These plaques may eventually block an artery, prevent blood from flowing through, and trigger a heart attack or stroke. Whew! Got all that? VLDLs and LDLs are sometimes called “bad cholesterol,” but this characterization is a misnomer. They aren’t cholesterol; they’re just the rafts on which cholesterol sails into your arteries.

Traveling through the body, LDLs continue to lose cholesterol. In the end, they lose so much fat that they become mostly protein — turning them into high-density lipoproteins, the particles sometimes called “good cholesterol.” Once again, this label is inaccurate.

HDLs aren’t cholesterol: They’re simply protein and fat particles too dense and compact to pass through blood vessel walls, so they carry cholesterol out of the body rather than into arteries. That’s why a high level of HDLs may reduce your risk of heart attack regardless of your total cholesterol levels.

Conversely, a high level of LDLs may raise your risk of heart attack, even if your overall cholesterol level is low. Hey, on second thought, maybe that does qualify them as “good” and “bad” cholesterol.

Setting limits on the bad guys

At one point, back in the dawn of the Cholesterol Age, like, say, five years ago, the “safe” upper limit for LDLs was assumed to be around 160 mg/dl.

Now, the National Heart, Lung, and Blood Institute, American College of Cardiology, and the American Heart Association have all put their stamps of approval on the National Cholesterol Education Program’s (NCEP) recommendations for new, lower levels of LDLs based on the presence of the risk factors I list under “Cholesterol and heart disease.”

You know — diabetes, high blood pressure, obesity . . . those risk factors. For healthy people with two or more risk factors, the new goal is to push LDLs below 130 mg/dl. For high-risk patients with heart disease or blood vessel problems and more than two risk factors, it’s LDLs below 100 mg/dl.

For very high-risk patients who are hospitalized with heart disease or have heart disease plus several risk factors, LDLs should be under 70 mg/dl. If necessary, the NCEP suggests using cholesterol-busting “statin” drugs such as atorvastatin (Lipitor).

Diet and cholesterol

Most of the cholesterol that you need is made right in your own liver, which churns out about 1 gram (1,000 milligrams) a day from the raw materials in the proteins, fats, and carbohydrates that you consume. But you also get cholesterol from food of animal origin: meat, poultry, fish, eggs, and dairy products.

Although some plant foods, such as coconuts and cocoa beans, are high in saturated fats, no plants actually have cholesterol. Table 2 lists the amount of cholesterol in normal servings of some representative foods. Because plants don’t contain cholesterol, no plant foods are on this list.

No grains. No fruits. No veggies. No nuts and seeds. Of course, you can juice plant food up with cholesterol if you really try: Butter in the bread dough, cheese on the macaroni, cream sauce on the peas and onions, whipped cream on poached peaches, and so on.

Food	Serving Size	Cholesterol (mg)
Meat
Beef (stewed) lean and fat	3 ounces	87
Beef (stewed) lean	2.2 ounces	66
Beef (ground) lean	3 ounces	74
Beef (ground) regular	3 ounces	76
Beef steak (sirloin)	3 ounces	77
Bacon	3 strips	16
Pork chop, lean	2.5 ounces	71
Poultry
Chicken (roast) breast	3 ounces	73
Chicken (roast) leg	3 ounces	78
Turkey (roast) breast	3 ounces	59
Fish
Clams	3 ounces	43
Flounder	3 ounces	59
Oysters (raw)	1 cup	120
Salmon (canned)	3 ounces	34
Salmon (baked)	3 ounces	60
Tuna (water canned)	3 ounces	48
Tuna (oil canned)	3 ounces	55
Cheese
American	1 ounce	27
Cheddar	1 ounce	30
Cream	1 ounce	31
Mozzarella (whole milk)	1 ounce	22
Mozzarella (part skim)	1 ounce	15
Swiss	1 ounce	26
Milk
Whole	8 ounces	33
2%	8 ounces	18
1%	8 ounces	18
Skim	8 ounces	10
Other dairy products
Butter	Pat	11
Other
Eggs, large	1	213
Lard	1 tbsp.	12

Nutritive Value of Foods (Washington, D.C.: U.S. Department of Agriculture)