The Macronutrients: Carbohydrates, Proteins And Fats
Chester J. Zelasko, Ph.D. | August 2004

The foods we eat contain nutrients. Carbohydrate, protein, and fat are considered macronutrients because we need a substantial amount of all three everyday to keep our bodies operating smoothly. They provide us with energy but they also have other important functions in our bodies you may not realize. For each energy nutrient, we'll find out:
  • What is the nutrient used for in our bodies besides energy?
  • How is the energy nutrient stored in our body?
  • What foods contain the energy nutrient?
  • What happens if we eat too much of it?

Carbohydrates are the body's primary source of energy for most activities. Carbohydrates are found in simple forms, such as fruit or table sugar, or complex forms, like whole wheat breads, rice, or potatoes -- but in all cases they're made up of smaller units. These smaller units are mostly glucose and fructose. The sugar lactose is primarily found in dairy products like milk. All are combinations of carbon, hydrogen, and oxygen in a perfect balance for use in the body. There are other minor sugars found in foods that are important for cellular communication.

Carbohydrates have one prime directive: provide your body's cells with energy to carry on cell functions. Glucose is the preferred source of energy for the brain -- real brain food -- and for muscles during physical activity. Carbohydrates contain about 4 calories per gram.

What’s a calorie? It is a unit of energy used to tell us how much potential energy is stored within food. Technically, it is the energy required to raise the temperature of 1 liter of water, 1 degree centigrade. If you can’t relate to that (as many of us cannot) just know that the more of those you take in, the more energy you have to use -- or store!

Glucose and fructose are stored in limited quantities in the body in the form of glycogen. The liver has the highest concentration of glycogen, but the muscular system stores a greater quantity of glycogen overall -- there is more muscle mass in an individual than liver mass. Your body attempts to keep a 24-hour supply (about ½ lb.) of glycogen so you always have a ready supply of glucose available under normal food-intake conditions.

Carbohydrate intake is converted to fat by the liver and stored in fat cells. Some fat is made this way every day and is necessary to stretch the energy we get from our food. Only when we chronically overeat does the excess fat that's made begin to show up in our favorite fat depositories.

Carbohydrates are found chiefly in vegetables, fruits, and grains, and are available in several forms classified under two basic categories:

Simple carbohydrates
These are sugar molecules, primarily glucose and fructose, that make up short chain-molecules. The primary source of simple carbohydrates in American diets are refined sugars such as table sugar, honey, and the corn syrup found in soft drinks. Also, most fruits are made up of simple sugars. What's the difference between the two? There is no difference in the way your body uses them -- glucose is glucose. The difference is in the concentration of sugar and the additional nutrients that may be supplied. For example, table sugar is made up of sucrose, a disaccharide made up of a glucose and a fructose, but nothing else. An apple contains sucrose but it also contains water, vitamins, minerals, and fiber. The energy received from one apple and 5 teaspoons of table sugar are the same, but you get more nutritional benefits from the apple.

Complex carbohydrates
These polysaccharides consist of long chains of glucose molecules. What the chains make depends on the arrangement of the glucose molecules -- wheat is arranged differently from potatoes, etc. Complex carbohydrates are found in wheat, rice, oats, corn, beans and legumes. Starches are found in plants such as potatoes and other tubers or roots. During digestion, your body "chops" the long chains into glucose units and that's the form absorbed into your bloodstream, ready for your body to use. Most complex carbohydrates, and fruits and vegetables as well, contain dietary fiber which is good for keeping your digestive system functioning properly and keeping you healthy.

Daily Intake
Total carbohydrate intake varies by how active you are. A sedentary person requires much less than a competitive athlete. In general, 40-70% of the Daily Intake should be from carbohydrates with an emphasis on whole grains, low-fat dairy, vegetables, and fruit; limit refined carbohydrates like soft drinks and sweets to no more than 10% of calories. In addition, adults should strive to eat 25-35 grams of fiber every day.

Ethyl alcohol or ethanol is made when enzymes in yeast’s transform carbohydrates into sugar. Depending on the type of carbohydrate used, the product will vary. If you use fruit, you get wine; if you use barley as the carbohydrate, you get beer. In order to make hard liquor, you need to further distill the initial product. The amount of ethanol found in wine, beer, or hard liquor varies. But the bottom line is this: for every gram of alcohol you drink, you take in 7 calories. It can be used for energy, but it must by metabolized to fat by the liver -- and you know where that fat ends up!

Warning: As this paper is written in 2004, we are in the midst of a “low-carb” obsession. People are counting carbohydrates in the hopes that it will contribute to weight loss. When viewing product labels, be sure to pay attention to the “Total Carbohydrate” section of the Nutrition Facts. While they may not effect blood sugar—and thus will not be claimed as carbs on the front of the product—they do contain calories. Read the product Ingredients carefully. Ingredients such as glycerin, maltitol and all sugar alcohols, and polydextrose contain calories and you will absorb them!

Proteins are made up of many thousands of smaller units called amino acids. Some amino acids can be made by the body while others have to be eaten in the foods we consume. Proteins are generally not used for energy by the body except under conditions of starvation, or prolonged, strenuous exercise like long distance cycling and running. The proteins that we eat are used to make:
  • Structural Fibers. Muscle is the best example of structural proteins, but there are many more. Proteins help make up the hardest substance in the body -- the enamel of your teeth. They also make up the tough fibers of your ligaments and tendons that keep your skeletal system (bones) together. Finally, they make up the cartilage that covers the ends of your bones and acts as a shock absorber.
  • Enzymes, the catalysts which speed up the millions of chemical reactions that occur every minute in your body.
  • Hormones such as insulin and glucagon which regulate your blood sugar.
  • The antibodies of your immune system which ward off bacterial and viral infections.
  • The elements of your blood that are responsible for clotting when you get cut.
  • and there are still more...

You can see that proteins have many functions in the body. Proteins contain about 4 calories per gram. But the lowest priority for proteins is to make energy for our normal activities.

Proteins aren't really stored in the body. By the nature of its structural function, muscle is the largest "storage" container of protein in the body. The building blocks of protein -- amino acids -- circulate in your bloodstream and lymph system and make up the metabolic amino acid pool. Proteins are constantly broken down and the component parts used again and again. This turnover rate is variable; some cells in your digestive system turnover in 3-4 days while cartilage cells take years to turnover. This variability is important because major organs like the liver and heart will be spared from breakdown during starvation at the expense of not-as-essential cells.

Just like with carbohydrates, your body will convert any extra energy from protein into fat and store it in your fat cells.

In the typical American diet, the sources of protein are meat, fish, and dairy products. The advantage is that the proteins are complete -- they contain all of the amino acids. However, most of these foods can also be high in fat and total calories. Beans, lentils and nuts are examples of vegetable sources of protein. Try to select foods that contain the highest amount of protein with the least amount of fat, especially saturated fat.

Some of the amino acids that your body needs to make proteins can be made by the body and some can’t. The ones that can’t are called essential amino acids. Do you need to eat meat to get all essential amino acids? Absolutely not, but it will take some effort to learn what foods to combine to receive all the amino acids your body needs. When we combine plant foods to ingest all of the essential amino acids, it’s called using complementary proteins. Depending on what type of vegetarian a person wanted to be, they would use some of the following combinations:

Grain and Milk
Cereal + Milk
Pasta + Cheese
Bread + Cheese

Grain and Bean & Legumes
Rice + Beans
Croutons + Split Pea Soup
Tortillas + Beans
Corn Bread + Chili beans
Brown Bread + Baked Beans

Legumes and Seeds
Tahini + Hummus
Tofu + Sesame Seeds

Daily Intake
The Food and Nutrition Council of the National Research Council recommends the following minimum protein consumption for adults: 0.8 grams/kg BW/day where kg stands for kilograms, BW stands for body weight, and Weight (kg) is your weight in kilograms. To convert your weight from pounds to kilograms, simply divide your weight (lbs.) by 2.2

Fats, also called lipids, are our primary source of energy while at rest. Lipids are composed of a molecule of glycerol and one to three fatty acids. Most fats are found with three fatty acids and are called triglycerides.

Fats are energy intensive, containing 9 calories per gram. But this isn't the only function of lipids in our body. The primary function of lipids is to form the membranes of each and every one of the cells of our body -- billions and billions of them. You've heard of the expression that "oil and water don't mix." That characteristic of lipids is very important because it regulates fluids in and out of our cells. Instead of passing through at will, water and other fluids have to move through special openings or channels in the membranes allowing the water content of each cell to be controlled. It's all possible because of lipids.

Another important function of lipids is that they’re used to make cholesterol. We've heard so much about how bad cholesterol is for you that we tend to overlook the importance of cholesterol. It works right next to lipids in the cell membranes and makes the membranes rigid and able to hold their shape. There are many more membrane functions thought to be attributed to cholesterol's presence, but the research continues. Cholesterol is also used to make hormones necessary for metabolism and sexual development.

Fat is also used for insulation and shock absorption. It protects organs and joints from the trauma of movement.

Fat is stored in the form of triglycerides. Unfortunately, we're all too familiar with where the fat cells are located. We can see the subcutaneous (or under the skin) fat stores all too well when we take off our clothes. Men tend to store fat on the back and around the waist while women tend to store fat around the hips and the thighs. However, half of your fat stores may be found under the muscle, surrounding the organs in the abdominal cavity. This "internal fat" is thought to be more dangerous than subcutaneous fat stores and is implicated in the development of cardiovascular disease, diabetes, and cancer.

Fats are found in animal foods including meat, fish, and dairy products, the oils derived from corn, olives, flaxseed, etc., and in nuts. Fresh fruits and vegetables are generally low in fat, but that doesn't mean all vegetable matter is. We like fats because they add so much flavor to the foods we eat. Think about it. What tastes better: a plain baked potato or a potato with butter and sour cream? Beef jerky or prime rib?

Daily Intake
Current recommendations are that less than 30% of your daily caloric intake should come from fat with no more than 10% of your daily intake from saturated fats. As part of the total fat intake, adults should consume 1.1-1.6 grams of omega-3 fatty acids from fish, flax, nuts, or dietary supplements.

Eating too much fat has serious health implications. Besides being stored as fat which leads to overweight and obesity, excess dietary fat can be converted to cholesterol. Serum cholesterol has been associated with the development of atherosclerosis; the higher your cholesterol, the greater the risk of heart disease. Excess weight is also associated with diabetes, cancer, gout, arthritis, sleep apnea, and many more conditions.

Facts about Fat
Dietary fats can vary in structure and how the body metabolizes them and therefore, can have differing effects on blood cholesterol.
  1. Saturated fats are hard at room temperature and generally come from animal sources, dairy products, or vegetable shortenings. Saturated fats increase blood cholesterol and are linked to heart disease.
  2. Monounsaturated fats are liquid at room temperature. Most fats contain some monounsaturated fat, but the richest source is olive oil. Monounsaturated fats help lower blood cholesterol levels.
  3. Polyunsaturated fats are liquid or soft at room temperature, and come from oils of fish, plant, or vegetable origin such as corn or soybean. Polyunsaturated fat is linked to heart disease prevention because it lowers blood cholesterol.
  4. Cholesterol makes up about 5% of dietary fat and is found in animal foods sources, along with saturated fat. The liver and intestinal wall also synthesize cholesterol.
  5. Trans-fatty acids are fats formed when oils are partially hydrogenated to make a more solid fat like margarine and shortening. Evidence continues to mount that trans-fatty acids raise blood cholesterol about as much as saturated fat does.
In today’s society, we are fortunate that food is abundant. With so many choices it can be difficult to eat to live, instead of living to eat. By understanding the composition of food, it’s role in your body, and what constitutes the best choices to make from the variety available, you can make an informed decision about how to eat to attain optimal health. That’s the better life way.
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