Last Updated: February 26, 2018
Carbohydrates, fats and proteins are macronutrients. We require them in relatively large amounts for normal function and good health. These are also energy-yielding nutrients, meaning these nutrients provide calories.
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Every few years, carbohydrates are vilified as public enemy number one and are accused of being the root of obesity, diabetes, heart disease and more. Carb-bashers shun yogurt and fruit and fill up on bun-less cheeseburgers. Instead of beans, they eat bacon. They dine on the tops of pizza and toss the crusts into the trash. They so vehemently avoid carbs and spout off a list of their evils that they may have you fearing your food. Rest assured, you can and should eat carbohydrates. In fact, much of the world relies on carbohydrates as their major source of energy. Rice, for instance, is a staple in Southeast Asia. The carbohydrate-rich potato was so important to the people of Ireland that when the blight devastated the potato crop in the mid 1800s, much of the population was wiped out.
The basic structure of carbohydrates is a sugar molecule, and they are classified by how many sugar molecules they contain.
Simple carbohydrates, usually referred to as sugars, are naturally present in fruit, milk and other unprocessed foods. Plant carbohydrates can be refined into table sugar and syrups, which are then added to foods such as sodas, desserts, sweetened yogurts and more. Simple carbohydrates may be single sugar molecules called monosaccharides or two monosaccharides joined together called disaccharides. Glucose, a monosaccharide, is the most abundant sugar molecule and is the preferred energy source for the brain. It is a part of all disaccharides and the only component of polysaccharides. Fructose is another common monosaccharide. Two common disaccharides in food are sucrose, common table sugar, and lactose, the source of frequent gas and bloating that some experience from drinking milk. Complex carbohydrates are any that contain more than two sugar molecules. Short chains are called oligosaccharides. Chains of more than ten monosaccharides linked together are called polysaccharides. They may be hundreds and even thousands of glucose molecules long. The way glucose molecules link together makes them digestible (starch) or non-digestible (fiber). Polysaccharides include the following.
Whether they’re from a doughy bagel, a sugary cola or a fiber-rich apple, carbohydrates’ primary job is to provide your body with energy. From each of these sources and others, carbohydrates provide you with 4 kcals/gram.
Carbohydrates, protein and fats are macronutrients, meaning the body requires them in relatively large amounts for normal functioning. The Recommended Dietary Allowance (RDA) for carbohydrates for children and adults is 130 grams and is based on the average minimum amount of glucose used by the brain.1 The Acceptable Macronutrient Distribution Range (AMDR) for carbohydrates is 45-65%. If, for instance, you ate 1600 kcals per day, the acceptable carbohydrate intake ranges from 180 grams to 260 grams.
Most American adults consume about half of their calories as carbohydrates. This falls within the AMDR, but unfortunately most Americans do not choose their carbohydrate-containing foods wisely. Many people label complex carbs as good and sugars as bad, but the carbohydrate story is much more complex than that. Both types yield glucose through digestion or metabolism; both work to maintain your blood glucose; both provide the same number of calories; and both protect your body from protein breakdown and ketosis. The nutrient-density of our food choices is far more critical. For example, fresh cherries provide ample sugars, and saltine crackers provide just complex carbs. Few would argue that highly processed crackers are more nutritious than fresh cherries.
Americans eat only 42% of the recommended amount of fruit and 59% of the recommended vegetable amount. We eat only 15% of the recommended servings of whole grains, but 200% of the recommended servings of refined grains.2 Americans over-consume added-sugars, which make up 16% of the total calories in the American diet. Nearly 60% of added sugars come from soda, energy drinks, sports drinks, fruit drinks and grain-based desserts like cakes, cookies and brownies.3 The problem with added sugars is that they do not come packaged with an abundance of nutrients like a piece of fruit and a glass of milk do. For this reason, many people call them empty calories.
Sometimes people look to the glycemic index (GI) to evaluate the healthfulness of carbohydrate-rich foods, but this too oversimplifies good nutrition. The GI ranks carbohydrate-containing foods from 0 to 100. This score indicates the increase in blood glucose from a single food containing 50 grams of carbohydrate compared to 50 grams of pure glucose, which has a GI score of 100. Foods that are slowly digested and absorbed - like apples and some bran cereals - trickle glucose into your bloodstream and have low GI scores. High GI foods like white bread and cornflakes are quickly digested and absorbed, flooding the blood with glucose. Research regarding the GI is mixed; some studies suggest that diets based on low GI foods are linked to lower risks of diabetes, obesity and heart disease, but other studies fail to show such a link.
Many factors influence a food’s GI score, including:
All of these factors complicate the usefulness of the GI. Additionally, many high-calorie, low-nutrient foods such as some candy bars and ice creams have desirable GI scores, while more nutritious foods like dates and baked potatoes have high scores. It’s important to recognize that the healthfulness of a food depends largely on its nutrient density, not its type of carbohydrate or its GI score.
Proponents of low-carbohydrate diets are incensed by the RDA and AMDR for carbohydrates. “Nutrition experts are trying to kill us,” they argue and claim that carbohydrates have made us overweight. However, research supports that diets of a wide range of macronutrient proportions facilitate a healthy weight, allow weight loss and prevent weight regain. The critical factor is reducing the calorie content of the diet long-term.45
If we shunned all carbohydrates or if we severely restricted them, we would not be able to meet our fiber needs or get ample phytochemicals, naturally occurring compounds that protect the plant from infection and us from chronic disease. The hues, aromas and flavors of the plant suggest that it contains phytochemicals. Scientists have learned of thousands of them with names like lycopene, lutein and indole-3-carbinol. Among other things, phytochemicals appear to stimulate the immune system, slow the rate at which cancer cells grow, and prevent damage to DNA.
All naturally fiber-rich foods are also rich in carbohydrates. The recommended intake for fiber is 38 grams per day for men and 25 grams per day for women. The usual fiber intake among Americans, however, is woefully lacking at only 15 grams daily. Perhaps best known for its role in keeping the bowels regular, dietary fiber has more to brag about. Individuals with high fiber intakes appear to have lower risks of coronary heart disease, stroke, hypertension, diabetes and obesity.6 Fiber-rich foods are protective against colorectal cancer7, and increasing fiber intakes improves gastroesophageal reflux disease and hemorrhoids.6 Some fibers also lower blood cholesterol and glucose levels. Additionally, fibers are food for the normal (healthy) bacteria that reside in your gut and provide nutrients and other health benefits. To boost your fiber intake, eat fruits, vegetables, whole grains and beans frequently.
Source: Dietary Guidelines for Americans, 2011 (Appendix 13)
Carbohydrates are critical sources of energy for several body systems. Nourish your body and help shield yourself from chronic disease by getting most of your carbohydrates from fruits, whole grains, legumes, milk and yogurt. Limit added sugars and heavily processed grains.
What’s for dinner? In the U.S, this question is usually answered with some type of meat like pot roast, chicken, salmon or meatloaf. Meat, because it’s rich in protein, is usually central to the meal, and vegetables and grains are frequently the afterthought. This may give the impression that a meal isn’t complete without meat and that we need lots of meat or protein for good health. The truth is, most Americans eat much more protein than their bodies require. And even if you choose to eat no meat at all, you can still meet your protein needs.
Like carbohydrates and lipids, proteins are one of the macronutrients. Though protein provides your body with 4 kcals per gram, giving you energy is not its primary role. Rather, it’s got way too many other things going on. In fact, your body contains thousands of different proteins, each with a unique function. Their building blocks are nitrogen-containing molecules called amino acids. If your cells have all 20 amino acids available in ample amounts, you can make an infinite number of proteins. Nine of those 20 amino acids are essential, meaning you must get them in the diet.
Bodybuilders drink protein shakes for breakfast and after working out. Dieters with no time to stop for lunch grab protein bars. Are these strategies necessary for optimal strength building and weight loss? Probably not.
Proteins in the body are constantly broken down and re-synthesized. Our bodies reuse most of the released amino acids, but a small portion is lost and must be replaced in the diet. The requirement for protein reflects this lost amount of amino acids plus any increased needs from growth or illness. The Recommended Dietary Allowance (RDA) for protein for adults is 0.8 g/kg of body weight. Because of their rapid growth, infants have the highest RDA for protein at 1.5 g/kg of body weight. The RDA gradually decreases until adulthood. It increases again during pregnancy and lactation to a level of 1.1 g/kg. The RDA for an adult weighing 140 pounds (63.6 kg) is a mere 51 grams of protein, an amount many of us consume before mid-afternoon.
The RDA remains the same regardless of physical activity level. There is some data, however, suggesting that both endurance and strength athletes have increased protein needs compared to inactive individuals. Endurance athletes may need as much as 1.4 g/kg, and strength athletes may require as much as 1.7 g/kg.8 A bodybuilder weighing 200 pounds (90.9 kg) may then need as much as 155 grams protein.
The Acceptable Macronutrient Distribution Range (AMDR) for protein for men and women age 19 and older is 10-35% of total calories. For children age 4 and over, it is 10-30%, and for younger children, the range is 5-20%. For an adult consuming 1600 kcals per day, the acceptable protein intake ranges from 40-140 grams per day, an amount easily met. Consider the 200-pound bodybuilder whose protein needs are approximately 155 grams per day. With energy needs approximately 4500 kcals per day, his protein needs are only 14% of his total calories — well within the AMDR. With his energy needs so great, however, his diet will need careful planning. If he requires engineered foods such as bars and shakes, it will most likely be to meet his energy needs rather than his protein needs.
One population that needs special attention is the elderly. Though the RDA for older adults remains the same as for younger adults, some research suggests their needs may be 1.2 grams/kg body weight in order to prevent the common muscle loss and osteoporosis that come along with aging.9 Though this doesn’t require the elderly to eat large servings of food, they frequently have poor appetites and dental problems that make chewing difficult. Helping them meet their nutritional needs may take a little creativity and perseverance.
People become vegetarian for a variety of reasons including religious beliefs, health concerns, and a concern for animals or for the environment. Oftentimes, “How can I get my protein?” is the first question asked when people discuss their choice for vegetarianism. Yes, in the typical American diet, most of our protein comes from animal foods. It is possible, however, to meet all of your protein needs while consuming a vegetarian diet. You can even eat adequate protein on a carefully planned vegan diet - a diet that excludes all animal products, including eggs and dairy.
When you think of protein, like most people, you probably think of beef, chicken, turkey, fish and dairy products. Beans and nuts might come to mind as well. Most foods contain at least a little protein, so by eating a diet with variety, vegetarians and vegans can eat all the protein they need without special supplements.
This list illustrates the amount of protein found in common foods that may be included in your diet.
A complete protein includes all of the essential amino acids. Complete proteins include all animal proteins and soy. Incomplete proteins lack one or more essential amino acids. Beans, nuts, grains and vegetables are incomplete proteins. Previously, registered dietitians and physicians advised vegetarians to combine foods that contained incomplete proteins at the same meal to give the body all the necessary amino acids it needed at one time. Today we know this is unnecessary. Your body combines complementary or incomplete proteins that are eaten in the same day.10
If you eat a variety of foods, you will meet your protein needs. Recreational athletes rarely need protein supplements. Professional athletes should consult a registered dietitian (RD) who is also a Certified Specialist in Sports Dietetics (CSSD). If you are vegetarian or vegan, it’s wise to see a registered dietitian for careful planning of your diet to meet not just your protein needs, but other nutrients as well.
It all started in the ’80s. Doctors, nutritionists and public health officials told us to stop eating so much fat. Cut back on fat, they said, to lose weight and fend off heart disease among other ills. Americans listened, but that didn’t improve our food choices. Rather, low-fat food labels seduced us, and we made pretzels and fat-free, sugar-rich desserts our grocery staples. Today we know to focus on the quality of the fat instead of simply the quantity.
Say NO to very low-fat diets. Why? Many people find them limiting, boring, tasteless and hard to stick to. And because fat tends to slow down digestion, many low-fat dieters fight hunger pangs all day or eat such an abundance of low-fat foods that their calorie intake is too great for weight loss.
Dietary fat has critical roles in the body. Each gram of fat, whether it’s from a spoon of peanut butter or a stick of butter, provides 9 kcals. This caloric density is a lifesaver when food is scarce and is important for anyone unable to consume large amounts of food. The elderly, the sick and others with very poor appetites benefit from high-fat foods. Because their tiny tummies can’t hold big volumes, small children too need fat to provide enough calories for growth.
Fats and oils (collectively known as lipids) contain mixtures of fatty acids. You may refer to olive oil as a monounsaturated fat. Many people do. Really, however, olive oil contains a combination of monounsaturated, saturated and polyunsaturated fatty acids, but it has more monounsaturated fatty acids than other types. Similarly, it is technically incorrect to call lard a saturated fat. It does contain mostly saturated fatty acids, but both monounsaturated and polyunsaturated fatty acids are present as well.
There is no Recommended Dietary Allowance (RDA) or Adequate Intake (AI) for total fat intake for any population other than infants. Depending on the age, the AI for infants is 30 or 31 grams of fat per day. The Acceptable Macronutrient Distribution Range (AMDR) is 20-35% for men and women age 19 years and older. For an adult consuming 1600 kcals then, the acceptable fat intake ranges from 35 to 62 grams daily. The AMDR for children is higher and varies by age, starting out at 30-40% for children ages 1 to 3 and gradually approaching the AMDR for adults. Experts discourage low-fat diets for infants, toddlers and young children because fat is energy-dense, making it appropriate for small, finicky appetites and to support growth and the developing central nervous system. The AIs for LA and ALA for adults range from 11-17 grams and 1.1 to 1.6 grams, respectively.
Because your body can make all the saturated fatty acids it needs, you do not need any in the diet. High intakes of most saturated fatty acids are linked to high levels of LDL (low-density lipoprotein), or bad, cholesterol and reduced insulin sensitivity.12 According to the Dietary Guidelines for Americans 2010, we should limit our intake of saturated fatty acids to 10% of our total calorie intake (18 grams for someone eating 1600 kcals daily) to reduce LDL cholesterol and our risk for heart disease. The American Heart Association favors a greater restriction to just 7% of total calories (12 grams for a 1600 kcal diet). If you tried to eat no saturated fatty acids, however, you would soon find that you had little to eat. Remember that fats are combinations of fatty acids, so even nuts and salmon (good sources of healthy fats) contain some saturated fatty acids.
What does bacon grease look like after the pan has cooled? Its firmness is a hint that bacon is high in saturated fat. Many saturated fats are solid at room temperature. Dairy fat and the tropical oils (coconut, palm and palm kernel) are also largely saturated. The greatest sources of saturated fat in the American diet are full-fat cheese, pizza and desserts.13
The benefit you experience from reducing your intake of saturated fats depends on many factors, including what you replace them with. Loading up on fat-free pretzels and gummy candies may be tempting, but is a misguided strategy because diets high in heavily refined carbohydrates typically increase triglycerides and lower the beneficial HDL (high-density lipoprotein) cholesterol, both risk factors for heart disease. A better strategy is to replace the foods rich in unhealthy fats with foods rich in healthy fats. Cooking with oils is better than cooking with butter or lard. A quick lunch of a peanut butter sandwich instead of a slice of pizza will do your heart some good. Trading out some of the cheese on your sandwich for a slice or two of avocado is another smart move. If your calories are in excess, switch from whole milk or 2% reduced-fat milk to 1% low-fat milk or nonfat milk to trim both calories and saturated fats.
Food manufacturers create both saturated and trans fats when they harden oil in a process called hydrogenation, usually to increase the shelf life of processed foods like crackers, chips and cookies. Partial hydrogenation converts some, but not all, unsaturated fatty acids to saturated ones. Others remain unsaturated but are changed in chemical structure. These are the health-damaging trans fats.
Many experts consider trans fats even worse than saturated fats because, like saturated fats, they contribute to insulin resistance14 and raise LDL cholesterol, but there’s more bad news. They also lower HDL cholesterol (the good cholesterol).15 The American Heart Association recommends that we keep our trans fatty acid intake to less than 1% of total calories (less than 2 grams if consuming 1600 calories daily). Achieving this might be trickier than you realize because many foods touting No Trans Fats on their labels actually contain traces of these artery-scarring fats. That’s because the law allows manufacturers’ to claim zero trans fats as long as a single serving contains no more than 0.49 grams. If you eat a few servings of foods with smidgens of trans fat like margarine crackers and baked goods, you can easily exceed the recommended limit.
Identify traces of trans fats by reading the ingredients lists on food labels. Partially hydrogenated oil is code for trans fat. You know that there are at least traces of trans fat present. When oil is fully hydrogenated (the label will say hydrogenated or fully hydrogenated), it will not contain trans fats. Instead, the unsaturated fatty acids have been converted to saturated fatty acids.
As discussed, unsaturated fatty acids improve blood cholesterol levels and insulin sensitivity when they replace saturated and trans fats. There are two classes of unsaturated fatty acids: monounsaturated fats and polyunsaturated fats.
Monounsaturated fat souces include avocados, nuts, seeds and olives. Peanut, canola and olive oils are additional sources.
There are several types of polyunsaturated fats, and they each have different roles in the body.
When you work on reducing whole-milk dairy, solid fats (like butter and bacon grease), and processed foods containing partially hydrogenated oils, be sure to replace them with unsaturated fats rather than simply adding extra calories to your usual diet. Otherwise you can expect to loosen your belt as you put on the pounds.
Don’t fear fats. Instead choose them wisely, making sure you do not exceed your calorie needs. Enjoy foods with monounsaturated and polyunsaturated fats while limiting the saturated and trans fats.
The National Academies Press. Chapter 6: Dietary Carbohydrates: Sugars and Starches IN Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids. http://www.nap.edu/openbook.php?record_id=10490&page=265 ↩
Dietary Guidelines for Americans, 2010. U.S. Department of Agricultural, U.S. Department of Health and Human Services, 2010: pg 46 ↩
Dietary Guidelines for Americans, 2010. U.S. Department of Agricultural, U.S. Department of Health and Human Services, 2010: pg 29 ↩
Dietary Guidelines for Americans, 2010. U.S. Department of Agricultural, U.S. Department of Health and Human Services, 2010: pg15 ↩
Dunford M, editor. Sports Nutrition: A Practice Manual for Professionals, 4th Edition. American Dietetic Association, 2006. ↩
Gaffney-Stromberg E, Insogna KL, et al. Increasing Dietary Protein Requirements in Elderly People for Optimal Muscle and Bone Health. J Am Geriatr Soc. 2009 Jun;57(6):1073-9. http://www.ncbi.nlm.nih.gov/pubmed/19460090 ↩
Vegetarian Diets. Position of the American Dietetic Association. J Am Diet Assoc. 2009;109: 1266-1282. ↩
Brown MJ, Ferruzzi MG, et al. Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings as measured with electrochemical detection. Am J Clin Nutr 2004;80:396-403. ↩
Dietary Guidelines for Americans, 2010. U.S. Department of Agricultural, U.S. Department of Health and Human Services, 2010: pg 26 ↩
Chardigny JM, Destaillats F, et al. Do trans fatty acids from industrially produced sources and from natural sources have the same effect on cardiovascular disease risk factors in healthy subjects? Results of the trans Fatty Acids Collaboration (TRANSFACT) studyAm J Clin Nutr March 2008 vol. 87 no. 3 ↩
Micronutrient Information Center. Linus Pauling Institute of Oregon State University. http://lpi.oregonstate.edu/infocenter/othernuts/omega3fa/ Accessed February 1, 2012. ↩