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, and the fat in food is called dietary fat.
With the exception of cholesterol and other sterols (a fatty substance that has no calories and provides no energy), dietary fats are high-energy nutrients. Gram for gram, fats have more than twice as much energy potential (calories) as protein and carbohydrates: 9 calories per fat gram versus 4 calories per gram for the other two. (For more calorie information, see Chapters 3 and 5.)
This chapter cuts the fat away from the subject of fats and zeroes in on what you really need to know.
Discovering How Your Body Uses Fats
Dietary fats are sources of energy that add flavor to food — the characteristic sizzle on the steak, so to speak. Unfortunately, some forms of this tasty nutrient may also be hazardous to your health. The trick is to separate the good from the bad.
Understanding what fats do for you
A healthy body needs fats to build body tissues and manufacture biochemicals such as hormones. Some of the adipose (fatty) tissue in your body is plain to see. For example, even though your skin covers it, you can see the fat deposits in female breasts, hips, thighs, buttocks, and belly or on the male abdomen and shoulders.
This relatively visible body fat
Provides a source of stored energy
Gives shape to your body
Cushions your skin (imagine sitting in a chair without your buttocks to pillow your bones)
Acts as an insulation blanket that reduces heat loss
Other body fat is 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 send the electrical messages that enable you to think, see, speak, move, and perform the multitude of tasks natural to a living body. Your brain is about 60 percent fat, giving a whole new meaning to the term “fat head.”
A constituent of hormones and other biochemicals such as vitamin D and bile.
A shock absorber that protects your organs (as much as possible) if you fall or are injured.
Pulling energy from fat
Although dietary fat has more energy (calories) per gram than protein and carbohydrates, your body has a more difficult time pulling the energy out of fatty foods than out of foods high in protein and carbs.
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 effects of lipases, the enzymes that break fats apart so you can digest them. As a result, fat is digested more slowly than proteins and carbohydrates, so you feel fuller, a condition called satiety (pronounced say-ty-eh-tee) 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 cholecystokinin alerts your gallbladder to release 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 produce 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 high-protein/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).
Defining Fatty Acids and Their Relationship to Dietary Fat
Like amino acids, which are the building blocks of protein (explained in Chapter 6), 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.
An essential fatty acid is one that your body needs but can’t 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 often argue 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 a measly 2 percent of the calories you get each day come from fat.
Focusing on the Fats in Food
Food contains three kinds of fats: triglycerides, phospholipids, and sterols. Here’s how they differ:
Triglycerides: Your body uses these fats to make adipose tissue and burns for energy.
Phospholipids: Phospholipids are hybrids — part lipid, part phosphate (a molecule made with the mineral phosphorus) — that ferry hormones and the fat-soluble vitamins A, D, E, and K through your blood and back and forth in the watery fluid that flows across cell membranes.
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.
Looking at the fatty acids in food
All the fats in food are combinations of fatty acids. Nutritionists characterize fatty acids as saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), or polyunsaturated fatty acids (PUFA), 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. (Trans fatty acids are hydrogenated fatty acids.) Because of those extra hydrogen atoms, hydrogenated fatty acids behave like saturated fats, clogging arteries and raising the levels of cholesterol in your blood.
One answer to the problem of hydrogenated fatty acids is plant sterols and stanols. Plant sterols are natural compounds in the oils in grains, fruits, and vegetables, including soybeans. Stanols are compounds created by adding hydrogen atoms to sterols from wood pulp and other plant sources; the first commercial stanol food was Benecol (bene = good, col = cholesterol) spread.
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 (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.
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 polyunsaturated fat. Note for math majors: Some 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.
Table 7-1 What Fatty Acids Are in That Fat or Oil?
* 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)
Identifying the foods with fats
Not all foods have fats. True, all animal foods, such as milk, meat, fish, and poultry, have naturally occurring fats. Some grains and some grain products do as well, naturally or from added ingredients such as the butter or margarine and eggs used to make cake and cookie batter. But fruits and vegetables are a whole different story. A very short list that includes olives and avocados does contain natural fats, but most foods in these categories are fat free. In short, 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. (Remembers, 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, fresh fruits, and fresh 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.
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. 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.
For several years, The Dietary Guidelines for Americans has proposed exactly what percentage of our daily calories should come from fats. As Chapter 16 explains, the 2015 edition takes a whole new look at dietary fat consumption, dropping specific numbers on how much or how little you should have each day, aiming instead for quality over quantity limits, a position that makes food plans such as the Mediterranean Diet with its emphasis on fats from plants even more attractive.
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. Never limit the fat in your baby’s diet without checking first with your pediatrician.
Considering Cholesterol and You
Surprise: Every healthy body needs cholesterol. Look carefully, and you will find cholesterol in and around your cells, in your fatty tissue, in your organs, in your brain, and in your glands. What’s it doing there? Plenty. Cholesterol
Protects the integrity of cell membranes
Helps 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 (for more about vitamin D, see Chapter 11)
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 ( liter) of blood. When you get your annual report from the doctor, your total cholesterol level looks something like this: 225 mg/dL. In other words, you have 225 milligrams of cholesterol in every tenth of a liter of blood. The more cholesterol you have floating in your blood, the more cholesterol is likely to cross into your arteries, where it may stick to the walls, form deposits that eventually block the flow of blood, and thus increase your risk of heart attack or stroke.
Lipoproteins
A lipoprotein is a fat 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 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
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 LDLs, although elevated levels of all LDLs are regarded as being strongly linked to an increased risk of cardiovascular disease, such as a blocked blood vessel leading to a heart attack.
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 increase your risk of heart attack, even if your overall cholesterol level is low.
Setting limits on the bad guys
At one point, back in the Dawn of the Cholesterol Age, the “safe” upper limit for LDLs was assumed to be around 160 milligrams per deciliter. 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.
Table 7-2 lays out the specifics on the National Cholesterol Education Program (NCEP) and the National Heart, Lung, and Blood Institute descriptions of and recommendations for total cholesterol levels, levels of high-density lipoproteins (HDLs), the so-called “good cholesterol,” and low-density lipoproteins, the so-called “bad cholesterol” that invades and may clog blood vessels.
Table 7-2 Rating the Levels of Cholesterol in Your Blood
For healthy people with two or more risk factors, the optimal level for LDLs is below 100 mg/dL; 100 to 129 mg/dL is considered near optimal/above optimal. Very high-risk patients, such as those who are hospitalized with heart disease or have heart disease plus several risk factors, are often told to push their LDLs under 70 mg/dL, a level virtually impossible to reach without a cholesterol-busting drug, usually a statin, such as atorvastatin (Lipitor).
But total cholesterol levels alone aren’t the entire story. Many people with high cholesterol levels live to a ripe old age, while others with low total cholesterol levels develop heart disease because cholesterol is only one of several risk factors for heart disease. Here are some more:
An unfavorable ratio of lipoproteins (see the next section)
Smoking
Obesity
Age (being older is riskier)
Sex (being male is riskier)
A family history of heart disease
Diet and cholesterol
Most of the cholesterol 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 produce cholesterol.
For the past several years, there has been an ongoing debate about whether the cholesterol in your food is as important in determining the levels of cholesterol in your blood as is the cholesterol you produce in your liver. In other words, for some people, it is possible that even a diet very low in cholesterol and saturated fats may not lower their own cholesterol levels. Chapter 16 gives you the lowdown on the conclusions drawn in the Dietary Guidelines for Americans 2015. Meanwhile, for those of you who prefer to track your dietary cholesterol, Table 7-3 lists the amount of cholesterol in normal servings of some representative foods.
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.
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. Never limit the fat in your baby’s diet without checking first with your pediatrician.
liter) of blood. When you get your annual report from the doctor, your total cholesterol level looks something like this: 225 mg/dL. In other words, you have 225 milligrams of cholesterol in every tenth of a liter of blood. The more cholesterol you have floating in your blood, the more cholesterol is likely to cross into your arteries, where it may stick to the walls, form deposits that eventually block the flow of blood, and thus increase your risk of heart attack or stroke.
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.
For the past several years, there has been an ongoing debate about whether the cholesterol in your food is as important in determining the levels of cholesterol in your blood as is the cholesterol you produce in your liver. In other words, for some people, it is possible that even a diet very low in cholesterol and saturated fats may not lower their own cholesterol levels.