THE MACRONUTRIENTS: CARBOHYDRATES, PROTEINS, AND FATS

There is no one perfect food. We need an assortment of nutrients that can be obtained only by eating a wide variety of foods. What is it that our bodies need? Scientists have identified more than 40 different nutrients in food. These substances are essential for growth and for the chemical reactions and processes that keep us alive and functioning (metabolism).

Except for an extremely small number of foods that consist almost entirely of one nutrient, the vast majority of the foods we eat are mixtures of many nutrients. Nevertheless, each group of foods included in the Food Guide Pyramid (grains, fruits and vegetables, milk products, and meats) is unique in the types of nutrients it contributes to our diets. For example, fruits and vegetables are the main source of many vitamins, minerals, and complex carbohydrates in our diets, and the meat group (including dry beans and legumes, eggs, poultry, and fish) is the main source of protein for most people.

It can be difficult to understand the difference between the nutrients themselves and the foods that contain them. For example, when you hear nutrition experts talk about the need to get more complex carbohydrates, what do they mean and what foods contain those nutrients? In this chapter, we focus on the nutrients themselves—how they are digested, what happens to them in the body, and what they do for you. We also say a little about the best food sources of each nutrient, because, after all, when you go to the supermarket, you don’t look for protein, starch, fiber, and antioxidants, you look for chicken, rice, raisin bran, and orange juice.

Nutrients are sorted into categories on the basis of their chemical structures and functions. Carbohydrates, proteins, and fats contained in foods are known as the macronutrients, because they are required in the largest quantities. In addition to their other functions, macronutrients provide energy in the form of calories. Vitamins and minerals are known as the micronutrients. They are required by your body in much smaller quantities. Although the micronutrients help your body use the energy in macronutrients, they provide no energy (calories) themselves. Water is also an essential, calorie- free nutrient. The work our bodies do each day causes us to deplete some of our stores of these essential nutrients. Only by maintaining a diet that is rich in various nutrient-containing foods can we replace those lost nutrients.

In addition to the known nutrients, substances in foods of plant origin, called phytochemicals or phytonutrients (phyto is the Greek word for plant), have been identified in recent studies. These phytochemicals may promote health and help prevent certain diseases. Hundreds of such compounds are being identified in the fruits, vegetables, nuts, beans, and grains we eat, although only a few have been thoroughly studied. How these various phytochemicals influence our health is a promising new area of research for nutrition experts.

THE MACRONUTRIENTS: CARBOHYDRATES, PROTEINS, AND FATS

Each of the macronutrients—carbohydrates, proteins, and fats—plays various roles in the function of our bodies. In addition to their unique functions, all of the macronutrients supply calories. When we eat more protein, carbohydrate, or fat than we need to replenish what we have used, the excess is converted to and stored as fat. Calories are used to support all muscular activity, to carry out the metabolic reactions that sustain the body, to maintain body temperature, and to support growth. But when we consistently take in more calories than we use, we gain weight. Weight is maintained when energy (calorie) intake balances energy output.

CARBOHYDRATES

The carbohydrates are a vast and diverse group of nutrients found in most foods. This group includes simple sugars (like the sugar you add to your morning coffee) and complex forms such as starches (contained in pasta, bread, cereal, and in some fruits and vegetables), which are broken down during digestion to produce simple sugars. The main function of the simple sugars and starches in the foods we eat is to deliver calories for energy. The simple sugar glucose is required to satisfy the energy needs of the brain, whereas our muscles use glucose for short-term bouts of activity. The liver and muscles also convert small amounts of the sugar and starch that we eat into a storage form called glycogen. After a long workout, muscle glycogen stores must be replenished. Both simple sugars and starches provide about 4 calories per gram (a gram is about the weight of a paper clip). Because carbohydrates serve primarily as sources of calories (and we can get calories from other macronutrients), no specific requirement has been set for them, The Dietary Reference Intakes [DRIs]. But health experts agree that we should obtain most of our calories (about 60 percent) from carbohydrates. Our individual requirements depend on age, sex, size, and activity level.

In contrast to the other carbohydrates, fiber (a substance contained in bran, fruits, vegetables, and legumes) is a type of complex carbohydrate that cannot be readily digested by our bodies. Even though it isn’t digested, fiber is essential to our health. Nutrition professionals recommend 25 to 30 grams of fiber daily.

Simple Sugars

Simple sugars make foods sweet. They are small molecules found in many foods and in many forms. Some simple sugars occur naturally in foods. For example, fructose is the sugar that naturally gives some fruits their sweet flavor. Table sugar, the sugar that we spoon onto our cereal and add to the cookies we bake, also called sucrose, is the most familiar simple sugar. A ring-shaped molecule of sucrose actually consists of a molecule of fructose chemically linked to a molecule of another simple sugar called glucose. Sugars such as fructose and glucose are known as monosaccharides, because of their single (mono) ring structure, whereas two-ringed sugars such as sucrose are known as disaccharides. Another disaccharide, lactose, the sugar that gives milk its slightly sweet taste, consists of glucose linked to yet another simple sugar called galactose. The inability to digest lactose to its constituent sugars is the cause of lactose intolerance, a condition common to adults of Asian, Mediterranean, and African ancestry.

The table sugar that we purchase is processed from sugar cane or sugar beets. As an additive to many different types of prepared or processed foods, sucrose adds nutritive value (in the form of calories only), flavor, texture, and structure, while helping to retain moisture. Today, sucrose is most often used to sweeten (nondietetic) carbonated beverages and fruit drinks (other than juice), candy, pastries, cakes, cookies, and frozen desserts. One of the most commonly consumed forms of sugar is called high-fructose corn syrup. High-fructose corn syrup is also commonly used to sweeten sodas, fruit drinks (not juices), some ice creams, and some manufactured pastries and cookies. Other forms of sucrose include brown sugar, maple syrup, molasses, and turbinado (raw) sugar.

Foods that are high in added sugar are often low in essential nutrients such as vitamins and minerals. Unfortunately, these foods are often eaten in place of more nutrient-rich foods such as fruits, vegetables, and low-fat whole-grain products, and they may prevent us from obtaining essential nutrients and lead to weight gain.

Nutritionists are concerned by the enormous increase in sugar consumption by Americans during the past 30 years, particularly because much of this sugar is in the form of soft drinks. On average, teens today drink twice as much soda as milk, and young adults drink three times as much soda as milk. As a result, their intake of calcium-rich foods is low, a factor that is thought to contribute to lower bone mass. This can lead to an increased risk of bone problems as we grow older.

The increase in sugar consumption also has been attributed to the increasing availability of low-fat versions of such dessert and snack foods as cookies, cakes, and frozen desserts. Often, the sugar content of these foods is high because sugar is used to replace the flavor lost when the fat is decreased. Sugar promotes tooth decay, when consumed in forms that allow it to remain in contact with the teeth for extended periods.

Thus, foods that are high in sugar, or sugar and fat, and have few other nutrients to offer appear at the top of the Food Guide Pyramid because they should be eaten sparingly. In contrast, choosing fresh fruits, which are naturally sweetened with their own fructose, or low-fat yogurt, which contains lactose (natural milk sugar), allows us to get the vitamins and minerals contained in those foods as well as other food components that contribute to health but may not have yet been identified.

On the positive side, there is no credible evidence to demonstrate that sugar causes diabetes, attention deficit-hyperactivity disorder, depression, or hypoglycemia. No evidence has been found that sugar-containing foods are “addictive” in the true sense of the word, although many people report craving sweet foods, particularly those that are also high in fat.

Complex Carbohydrates

Found almost exclusively in foods of plant origin, complex carbohydrates are long chains of molecules of the simple sugar glucose. The complex carbohydrates in plant foods can be divided into two groups: starch and fiber.

Starch is the form of carbohydrate that is found in grains, some fruits and vegetables, legumes, nuts, and seeds. It provides energy for newly sprouting plants. Fiber is the tougher material that forms the coat of a seed and other structural components of the plant. Starches are digested by our bodies into their constituent glucose molecules and used for energy, whereas fiber is not. Starch, like simple sugars, provides 4 calories per gram, whereas fiber (sometimes called nonnutritive fiber) provides no calories. Like simple sugars, the role of starches in our diets is mainly to provide energy.

Fiber is actually a family of substances found in fruits, vegetables, legumes, and the outer layers of grains. Scientists divide fiber into two categories: those that do not dissolve in water (insoluble fiber) and those that do (soluble fiber). Insoluble fiber, also called roughage, includes cellulose, hemicellulose, and lignin, found in vegetables, nuts, and some cereal grains. Soluble fibers include pectin, found in fruits, and gums, found in some grains and legumes.

Fiber-rich diets, which include ample amounts of whole-grain foods, legumes, and fresh vegetables and fruits, have been linked with a lower risk of several diseases. Nutrition scientists are just beginning to understand the role of dietary fiber in maintaining health. Fiber appears to sweep the digestive system free of unwanted substances that could promote cancer and to maintain regularity and prevent disorders of the digestive tract. Fiber also provides a sense of fullness that may help reduce overeating and unwanted weight gain. Diets that are rich in fiber and serum cholesterol and a lower risk for high blood pressure, coronary artery disease, and some types of cancer. But does this mean that it’s okay just to take a fiber pill? No! Rather, the studies that have shown the beneficial effects of a high-fiber diet (containing 25 to 30 grams of fiber per day) have been those in which the dietary fiber is in the form of fruits, vegetables, whole grains, and cereals. These and other studies suggest that not only the fiber in these foods but also the vitamins, minerals, and other compounds they contain contribute to their health-promoting effects.

The Dietary Guidelines for Americans recommend that we obtain most (about 60%) of our calories from carbohydrates, preferably complex carbohydrates, in the form of foods such as whole grains, fruits, vegetables, and legumes. These foods are good sources of fiber, essential vitamins, minerals, and other phytochemicals and are also more likely to be low in fat.

The average American today consumes only about a third of the recommended amount of fiber. To obtain as many of the potential benefits as possible, you need to obtain complex carbohydrates and fiber from various food sources. Although studies indicate that our intake of carbohydrates is increasing, the contribution of whole-grain foods remains small, partly because identifying whole-grain foods can be confusing.

Foods that are naturally good sources of fiber or have fiber added are allowed to make claims on their labels regarding their fiber content. What do the terms used to describe fiber content mean? When you see the phrase “high fiber” on a food label, it means that 1 serving (defined on the Nutrition Facts panel) of the food contains 5 grams of fiber or more per serving. A food that contains 2.5 to 4.9 grams of fiber in a serving is allowed to call itself a “good source” of fiber, and a food label that says “more fiber” or “added fiber” has at least 2.5 grams more fiber per serving.

Sugar Substitutes

For the same reason that people have recently sought substitutes for fat, noncaloric sugar substitutes became popular in the 1960s as people began to try to control their weight. Sugar substitutes are of two basic types: intense sweeteners and sugar alcohols.

Intense sweeteners are also called non-nutritive sweeteners, because they are so much sweeter than sugar that the small amounts needed to sweeten foods contribute virtually no calories to the foods. These sweeteners also do not promote tooth decay. Currently, four such intense sweeteners are available, both for use in processed foods and for home consumption. The U.S. Food and Drug Administration (FDA) has set “acceptable daily intakes” (ADI) for these sweeteners. The ADI is the amount that can be consumed daily over a lifetime without risk.

One of these sweeteners is aspartame (NutraSweet brand). It is manufactured by chemically modifying the naturally occurring amino acid phenylalanine. This sweetener can’t be used by people with phenylketonuria (a rare congenital disorder that disrupts the body’s ability to metabolize phenylalanine and can result in severe nerve damage). Despite extensive safety testing showing aspartame to be safe, its use has been implicated by the popular press in everything from headaches to loss of attentiveness. At this time, there is no scientific validity to these claims. Aspartame is not heat stable, so it can’t be added to foods that will be cooked or baked, although it can be added to some foods (such as coffee) after heating.

Saccharin, a second non-nutritive sweetener, was associated with cancer in mice when it was fed in very large amounts. However, further studies have found no links between saccharin and human cancer. This recently led the U.S. government to remove it from its list of potential cancer-causing chemicals. Although saccharin is heat stable, in some cases it cannot satisfactorily be used in baking because it lacks the bulk of sugar.

Acesulfame K (Sunnett), a third intense sweetener, was approved by the FDA in 1998 for use in soft drinks, although it was used in various food products before that. About 200 times sweeter than sugar, this noncaloric product has been extensively tested for safety. After reviewing more than 90 studies, the FDA deemed the sweetener safe in amounts up to the equivalent of a 132-pound person consuming 143 pounds of sugar annually (an Acceptable Daily Intake of 15 milligrams per kilogram of body weight; 1 kilogram is about 2.2 pounds). Because it is not metabolized, acesulfame K can be used safely by people with diabetes.

The sweetener is more heat stable than aspartame, maintaining its structure and flavor at oven temperatures more than 390° Fahrenheit and under a wide range of storage conditions. Like saccharin and aspartame, acesulfame K lacks bulk, so its use in home baking requires recipe modification. The flavor of acesulfame K has been described as clean and quickly perceptible, although disagreement exists about whether it leaves an aftertaste.

A fourth intense sweetener, sucralose (Splenda), was approved by the FDA in 1998 for sale and use in commercial food products. Sucralose is made by chemically modifying sucrose (table sugar) to a non-nutritive, non-caloric powder that is about 600 times sweeter than sugar. Before approving sucralose, the FDA reviewed more than 110 research studies conducted in both human and animal subjects. It concluded that the sweetener is safe for consumption by adults, children, and pregnant and breastfeeding women in amounts equivalent to the consumption of about 48 pounds of sugar annually (an Acceptable Daily Intake of 5 milligrams per kilogram of body weight).

People with diabetes may also safely consume the sweetener, because it is not metabolized like sugar. In addition, sucralose is highly stable to heat and so will not lose its sweetness when used in recipes that require prolonged exposure to high temperatures (such as baking) or when stored for long periods. The product is currently available in the form of a powdered sugar substitute and in some commercial baked goods, jams and jellies, sweet sauces and syrups, pastry fillings, condiments, processed fruits, fruit juice drinks, and beverages, and its use is approved for various additional products. However, use of sucralose in home baking is expected to be limited by its low bulk in comparison with table sugar.

Foods containing intense sweeteners should not be given to infants or children, who need energy to grow and to sustain their high activity levels. Foods that contain intense sweeteners and lack any nutritive value also should not replace nutrient-dense foods in your diet.

The sugar alcohols xylitol, mannitol, and sorbitol contain less than 4 calories per gram. These sugar alcohols are digested so slowly that most are simply eliminated. Unfortunately, excessive consumption can cause diarrhea or bloating in some people.

So-called “natural” sweeteners provide the same number of calories as sugar and have acquired the reputation, albeit incorrectly, of being healthier than sugar, because they seem more natural than processed table sugar. These include honey, maple syrup and sugar, date sugar, molasses, and grape juice concentrate. In reality, these sweeteners contain no more vitamins or minerals than table sugar. Honey may harbor small amounts of the spores of the bacteria that produce botulism toxin and should never be given to babies younger than 1 year

The Bottom Line on Carbohydrates 

Carbohydrates—sugars and starches—are the main source of fuel for our bodies. When we choose carbohydrate-rich foods, our best bets are fruits, vegetables, whole grains, and legumes, because these foods are also rich sources of health-promoting vitamins, minerals, phytochemicals, and fiber. But like all calories, extra calories from carbohydrates beyond those we need to replenish the energy we burn are converted to fat and stored in our fat cells. Non-caloric sweeteners seem to be a safe alternative to sugar for most people, but the foods that contain them are often nutritionally empty and their use in home cooking is limited. The so-called natural sweeteners are no better for you than sugar.

PROTEIN

Protein is an essential part of our diets. Proteins are large, complex molecules resembling tangled strings of beads. Each of the “beads” on the string is one of a group of smaller molecules called amino acids. Amino acids are composed of carbon, oxygen, hydrogen, and nitrogen, and some contain sulfur.

Using the amino acids from the protein you eat, the body makes more than 50,000 different proteins. These proteins are the main structural elements of our skin, hair, nails, cell membranes, muscles, and connective tissue. Collagen, the main protein in our skin, provides a barrier to the invasion of foreign substances. Proteins in cell membranes determine what substances can enter and exit cells.

Our muscles, which contain some 65 percent of the body’s total protein, give our bodies their shape and strength. Proteins in connective tissues such as tendons, ligaments, and cartilage enable our skeletons to function, form internal organs, and hold the organs in place. Proteins in the blood carry oxygen to all cells and remove carbon dioxide and other waste products. The proteins in muscle, connective tissue, and blood make up most of the protein in the body. Other proteins called enzymes accelerate metabolic processes, and still other proteins and amino acids are hormones and neurochemicals, the substances that deliver signals throughout the body and regulate all metabolic processes.

During periods of growth, our bodies must manufacture and store large amounts of protein. Therefore, the requirement for protein in our diets is higher during growth. But even when we are not growing, each of the unique proteins in the body has a finite lifespan and must be replaced continuously. So the need for protein never ends.

Dietary Protein and Body Protein

The thousands of proteins that make up our bodies are assembled on demand from some 20 different amino acids. What are these amino acids, and where do they come from? The protein from the meat we ate last night is not directly incorporated into our muscles. The proteins in the foods we eat are digested first into small “peptides.” Some of these peptides are further digested into their constituent amino acids. Only amino acids and small peptides are actually absorbed by the small intestine into the bloodstream. They are then delivered to the liver, muscles, brain, and other organs, where they are used to make new proteins or converted to other amino acids needed by those organs.

Of the 20 amino acids that make up all proteins, 9 are considered “essential” because they cannot be made in our bodies and must be obtained from the foods we eat. Of the remaining 11, some are essential for infants and persons with certain diseases. The rest of the amino acids are considered “nonessential,” because our bodies can make them in adequate amounts, if necessary. Nevertheless, they are easily supplied by eating a well-balanced diet that includes a variety of foods.

Most foods contain protein. Some foods are better sources of protein than others. “Complete” proteins are those that contain all the essential amino acids in amounts needed to synthesize our body’s proteins. The best sources of complete protein are lean meats and poultry, fish, low-fat dairy products, and eggs.

The grains and cereals group of foods, which form the base of the Food Guide Pyramid, are excellent sources of protein, but because these proteins often lack one or more essential amino acids, they are called “incomplete” proteins. For example, the proteins in corn are low in the essential amino acids lysine and tryptophan, and wheat is low in lysine. In contrast, legumes tend to be rich in lysine but a bit low in methionine. Among the legumes, soybeans contain the most complete protein.

Does this mean you must eat meat, eggs, and dairy products (foods of animal origin) to get all the amino acids you need? Not at all. By eating a variety of different foods, including grains and legumes, you are likely to get all the amino acids you need and in the correct amounts. People of many cultures and vegans (vegetarians who eat no foods of animal origin) get adequate amounts and types of protein by eating various combinations of plant proteins including beans, corn, rice, and other cereal grains. Although it was once thought necessary to combine these foods at the same meal, nutrition experts now agree that they can be eaten at various times throughout the day.

When we eat grains and legumes, rather than foods of animal origin (a more frequent source of protein in our diets), we gain additional health benefits. Whole-grain foods and legumes are rich in vitamins, minerals, fiber, and other substances that optimize health. If that does not seem like reason enough to make the trade, grains and legumes lack the high levels of saturated fat present in foods of animal origin, which, as you will learn below, are linked to many diseases.

Contrary to popular belief, simply eating more dietary protein, in excess of recommended amounts, will not result in bigger muscles. Our bodies do not store excess protein. If we eat more protein than our bodies need to replenish the amino acids we have used during the day, the excess amino acids are converted to, and stored as, fat. Dietary protein, like carbohydrates, supplies about 4 calories of energy per gram. Because our requirements for protein mainly depend on our body’s size, our need for protein increases during times of rapid growth. Therefore, the recommendations for protein are age-dependent and are slightly higher for pregnant and breastfeeding women than for other adults. The recommended allowances ensure an adequate protein intake by nearly all healthy people. Nevertheless, many Americans typically consume twice this amount, often in the form of meat and dairy products that are high in saturated fat, which increases the risk for coronary artery disease and some forms of cancer.

What if we eat too little protein? Few Americans are at risk of eating too little protein. However, individuals on severely restricted diets, those who are unable to eat, and those whose needs are increased because of illness or trauma may experience protein deficiency. To replenish the pools of essential amino acids that have been depleted, in order to make critical proteins such as enzymes and hormones, the body of a protein-deficient person begins to rob protein from muscle by digesting that protein to its constituent amino acids. Because muscle is needed for various vital functions (for example, diaphragm muscles for breathing and heart muscles for pumping our blood), the loss of large amounts of muscle protein can be fatal. Fortunately, the vast majority of people, even those who engage in regular, rigorous endurance exercise, can easily meet their need for protein by eating a balanced diet based on the Food Guide Pyramid.

The Bottom Line on Protein

Adequate protein is critical for growth, metabolism, and health, but eating more protein than we need will not build bigger muscles. Conversely, excess protein is converted to fat. Foods of animal origin are high in protein but may also be high in total and saturated fat. Lean meats and dairy products, fish, legumes, and grains are the best sources of protein.

FATS

It’s difficult to read a newspaper or listen to the evening news without hearing something new about fat and its connection with disease. Diets that are high in fat are strongly associated with an increased prevalence of obesity and an increased risk of developing coronary artery disease, high blood pressure, diabetes mellitus, and certain types of cancer. Health authorities recommend that we reduce our total fat intake to about 30 percent of total calories. They also recommend that we limit our intake of saturated fat (the type of fat most often found in meat and dairy products) to less than 10 percent of our fat calories and try to be sure that the fat we do eat is mostly the monounsaturated or polyunsaturated type. These changes have been shown to decrease our risk for several diseases.

Fat as a Nutrient

Fat is an essential nutrient, because our bodies require small amounts of several fatty acids from foods (the so-called essential fatty acids) to build cell membranes and to make several indispensable hormones, namely, the steroid hormones testosterone, progesterone, and estrogen, and the hormone-like prostaglandins. Dietary fats also permit one group of vitamins, the fat-soluble vitamins (A, D, E, and K), to be absorbed from foods during the process of digestion. Fats help these vitamins to be transported through the blood to their destinations. The fat in our bodies also provides protective insulation and shock absorption for vital organs.

As a macronutrient, fat is a source of energy (calories). The fat in food supplies about 9 calories per gram, more than twice the number of calories as the same amount of protein or carbohydrate. As a result, high-fat foods are considered “calorie-dense” energy sources. Any dietary fat that is not used by the body for energy is stored in fat cells (adipocytes), the constituents of fat (adipose) tissue. The Dietary Guidelines for Americans recommend that no more than 30 percent of our calories should come from fat, and only a third of that should be saturated fat.

Sorting Out the Fats

Our health is influenced by both the amount and the type of fat that we eat. Fats are molecules; they are classified according to the chemical structures of their component parts. But you don’t need to be a chemist to understand the connection between the various fats in foods and the effect these fats have on the risk for disease. Some definitions will help.

Dietary fats, or triglycerides, are the fats in foods. They are molecules made of fatty acids (chain-like molecules of carbon, hydrogen, and oxygen) linked in groups of three to a backbone called glycerol. When we eat foods that contain fat, the fatty acids are separated from their glycerol backbone during the process of digestion.

Fatty acids are either saturated or unsaturated, terms that refer to the relative number of hydrogen atoms attached to a carbon chain. Fat in the foods that we eat is made up of mixtures of fatty acids—some fats may be mostly unsaturated, whereas others are mostly saturated.

Monounsaturated fatty acids are fatty acids that lack one pair of hydrogen atoms on their carbon chain. Foods rich in monounsaturated fatty acids include canola, nut, and olive oils; they are liquid at room temperature. A diet that provides the primary source of fat as monounsaturated fat (frequently in the form of olive oil) and includes only small amounts of animal products has been linked to a lower risk of coronary artery disease. This type of diet is commonly eaten by people who live in the region surrounding the Mediterranean Sea.

Polyunsaturated fatty acids lack two or more pairs of hydrogen atoms on their carbon chain. Safflower, sunflower, sesame, corn, and soybean oil are among the sources of polyunsaturated fats (which are also liquid at room temperature). The essential fatty acids, linoleic and linolenic acid, are polyunsaturated fats. Like monounsaturated fats, polyunsaturated fats lower blood cholesterol levels and are an acceptable substitute for saturated fats in the diet.

Saturated fatty acids, or saturated fats, consist of fatty acids that are “saturated” with hydrogen. These fats are found primarily in foods of animal origin—meat, poultry, dairy products, and eggs—and in coconut, palm, and palm kernel oil (often called “tropical oils”). Foods that are high in saturated fats are firm at room temperature. Because a high intake of saturated fats increases your risk of coronary artery disease, nutrition experts recommend that less than 10 percent of your calories should come from saturated fats.

Omega-3 fatty acids are a class of polyunsaturated fatty acids found in fish (tuna, mackerel, and salmon, in particular) and some plant oils such as canola (rapeseed) oil. These fatty acids have made the news because of the observation that people who frequently eat fish appear to be at lower risk for coronary artery disease. Omega-3 fatty acids also seem to play a role in your ability to fight infection.

Hydrogenated fats are the result of a process in which unsaturated fats are treated to make them solid and more stable at room temperature. The hydrogenation process, which involves the addition of hydrogen atoms, actually results in a saturated fat. Trans-fatty acids are created by hydrogenation. An increase in consumption of these fats is a concern because they have been associated with an increased risk of coronary artery disease. Hydrogenated fat is a common ingredient in stick and tub margarine, commercial baked goods, snack foods, and other processed foods.

Cholesterol is a waxy, fat-like substance that is a necessary constituent of cell membranes and serves as a precursor for bile acids (essential for digestion), vitamin D, and an important group of hormones (the steroid hormones). Our livers can make virtually all of the cholesterol needed for these essential functions. Dietary cholesterol is found only in foods of animal origin, that is, meat, poultry, milk, butter, cheese, and eggs. Foods of plant origin, that is, fruits, vegetables, nuts, seeds, legumes, grains, and the oils derived from them, do not contain cholesterol. Eggs are the food most often associated with cholesterol, because the average large egg contains about 210 milligrams of cholesterol (only in the yolk), and the recommended daily cholesterol intake is 300 mg or less. However, for most people, meat contributes a higher proportion of cholesterol to the diet than do eggs, because cholesterol is found in both the lean and fat portions of meat. Shellfish have acquired an undeserved reputation for being high in cholesterol. Their cholesterol and total fat contents are actually comparatively low.

Fat Substitutes

To appeal to our desire for lower-fat substitutes for our favorite high-fat foods, the commercial food industry has developed low- or lower-fat versions of many foods using various fat replacers. Until recently, fat replacers always consisted of proteins or carbohydrates, such as starches or gels, but the kinds of foods that could be prepared with these fat replacers were limited by their inability to withstand the high temperatures of frying. In 1996, after a long period of development, safety testing, and governmental review, the first non-caloric fat, olestra, was approved by the FDA for use in the manufacture of savory (non-sweet) snacks (such as crackers and chips). Because olestra is a modified fat, it is the first heat-resistant fat substitute, which allows it to be used to make fried foods. In addition, olestra gives foods the flavor and creamy “mouth feel” of high-fat foods.

FDA approval of olestra was controversial for two reasons. First, this artificial ingredient, if approved and accepted, would be the first in history to be consumed in quantities comparable to the quantities of fat, carbohydrates, and proteins we currently consume from food sources. In other words, these novel, previously unknown substances could become major parts of the diets of some people, and there would be no historical experience to tell us what the substances might do in our bodies. Some scientists predicted that the substance would cause serious gastrointestinal complaints despite controlled studies demonstrating its safety. However, in the first year of availability of olestra-containing foods, the predicted intestinal problems were not significant. Tests in which volunteers ate large quantities of olestra-containing potato chips or regular potato chips without knowing which type they were eating showed no differences in gastrointestinal complaints between the two groups. Second, tests of olestra showed that it inhibits the absorption of fat-soluble compounds (vitamins A, D, E, and K and some carotenoids) from foods eaten at the same time as the olestra-containing foods, whereas it has no effect on the absorption of other nutrients or on the body’s stores of fat-soluble vitamins. To compensate for this effect of olestra on fat-soluble vitamin absorption, foods prepared with olestra have small amounts of these vitamins added to them. At this writing, the range of foods that can include olestra as a fat substitute is quite narrow. Some questions do remain about the long-term safety of the product, although long-term studies in young, growing animals and several studies in humans have shown no negative effects.

How should you decide whether to include foods with fat replacers in your eating plan, and how much of these foods do you include? From a health standpoint, small amounts of olestra-containing foods appear to be harmless. But from a purely nutritional standpoint, most foods that contain fat replacers are snack foods essentially devoid of nutritional benefit. In addition, these foods are not calorie-free. Many remain high in calories, and some foods that contain carbohydrate fat replacers are even higher in calories than their higher-fat counterparts, so they are still caloriedense, nutritionally poor foods. It’s fine to choose small amounts of these foods occasionally, but better low-fat snack choices include fruits, vegetables, nonfat yogurt, and whole-grain pretzels and breads.

The Bottom Line on Fats

Dietary fat is a source of energy, but high-fat diets, especially diets high in saturated fat, increase the risk of gaining excessive amounts of weight and of developing diabetes, coronary artery disease, high blood pressure, and several types of cancer. This increased risk is the reason that health experts encourage us to reduce our intake of total and saturated fats by:
• increasing our intake of fruits, vegetables, and wholegrain foods, which are naturally low in fat, and preparing them with a minimum of added fats
• consuming low-fat dairy products such as nonfat milk and yogurt and reduced-fat cheeses
• limiting our intake of red meat, poultry, and fish to 5 to 7 ounces daily
• choosing lean cuts of red meat and poultry, removing the skin before eating poultry, and preparing the meat with a method that uses little or no additional fats
• choosing some fish that is high in omega-3 fatty acids and preparing it with little or no added fat


By the Medical and Nutrition Experts from Mayo Clinic, University of California, Los Angeles and Dole Food Caompany, Inc. Editors-in-Chief: Robert A. Rizza, M.D., Vay Liang W. Go., M.D., M. Molly McMahon, M.D., Gail G. Harrison, Ph.D., R.D. in "Encyclopedia of Foods - A Guide to Healthy Nutrition", Academic Press (an imprint of Elsevier), San Diego, California, USA, 2002, excerpts chapter 2, pp.17-29. Adapted and illustrated to be posted by Leopoldo Costa.