Making good nutrition choices starts with an understanding of the basics. Here is a general overview of the main nutrients essential for our bodies to function so click on any of the topics in the chart below.
This information is not meant to be all-encompassing but to give you a quick idea of how food is metabolized by our bodies. We encourage you to learn more using the resources listed below or by asking your Bon Appétit dietitian.
Macronutrients refer to the three energy-yielding nutrients, carbohydrate, protein and fat. “Energy-yielding” means that they provide energy for our bodies in the form of calories. On the other hand, micronutrients, which include vitamins and minerals, do not provide energy but are essential for metabolic reactions to occur.
Carbohydrates are the primary source of fuel for our bodies, yielding four calories for every gram of carbohydrate. They are categorized as “simple” or “complex” based on their molecular structure. Complex carbohydrates (such as fiber) are broken down into simple carbohydrates (like glucose) so that the body can absorb and metabolize the energy.
After the carbohydrate is broken down into glucose, it’s absorbed into the bloodstream and then transported throughout the body. Naturally, blood glucose levels rise after a meal and then fall back after the glucose is delivered to cells. Because glucose is so critical for all cells in the body, there needs to be a constant supply of it in the blood stream. Maintaining this level involves a complicated process that requires various hormones, such as insulin and glucagon.
The inability of the body to maintain steady blood glucose levels is called diabetes.
Once the immediate needs of the body have been met, excess glucose is stored in the liver as glycogen. This serves as an “emergency reserve” just in case blood glucose levels drop too low (due to starvation, for example) but it can only sustain the body for a short period of time less than one day. This is why it’s necessary to have a constant carbohydrate intake, to provide your body with the energy it needs. Overall, carbohydrates should comprise about half of the calories you consume daily.
Carbohydrates (both simple and complex) are found in a wide range of foods: breads, pastas, rice, fruits, vegetables, beans, juices, sodas, milk, yogurt, cheese, and sweets. Table sugar and corn syrup are examples of simple carbohydrates; whole grains (oat, whole wheat, bran) and beans are examples of complex. Complex carbohydrates foods are highly recommended because of the health benefits of fiber.
Protein is very important because it provides structure for many parts of the body. For example, our bones, skin, and hair are made up of collagen, a matrix of protein and minerals. Protein is also essential for maintaining lean body muscle and also provides energy for the body–four calories per one gram of protein.
Proteins are composed of amino acids, the “building blocks” of protein. There are about 20 amino acids and almost half of them are “essential,” which means that the body can’t produce them so they need to be obtained through food. The “non-essential” amino acids are produced by the body in sufficient amounts.
Protein in foods (like meats or beans) doesn’t get directly utilized by the body. Instead, it is digested and broken down into amino acids before it is absorbed and transported throughout the body. The individual amino acids are then used to build specific proteins the body needs. This can range from enzymes and hormones to collagen and antibodies (molecules that fight disease).
When we hear “protein foods,” we tend to automatically think “meat.” Although meats, eggs and dairy products are great sources of protein, beans (soy, pinto, kidney, chickpeas, and lentils) and whole grains provide protein in our diet as well. About 20% of your daily calories should come from protein, a level which the average U.S. diet sufficiently meets.
Contrary to popular belief that “fat is bad,” fat is essential for our bodies to survive. Body fat is necessary for insulation and there are select vitamins that depend on fat for absorption and transport. And as we all know, fat contributes flavor in food.
Fat refers to a class of nutrients called “lipids,” which includes phospholipids, sterols and triglycerides (fats and oils).
Types of fats
Phospholipids and sterols only account for about 5% of fat in the body but are essential for many bodily functions. Phospholipids are the main component of all cell membranes and sterols are the basis of various hormones including cortisol, estrogen, testosterone and cholesterol.
Although cholesterol is necessary for hormone production, too much cholesterol in the blood can get deposited into and harden your artery walls. This health condition is called atherosclerosis, which can lead to heart attacks and strokes.
Triglycerides are the main lipids found in food and throughout the body. Although most fatty acids can be produced in the body, there are some “essential fatty acids,” including omega-3s and omega-6s, which must be obtained from our food. The chemical structure of the fatty acids determines their characteristics in foods.
Saturated fats are solid at room temperature so foods that are high in saturated fat include butter, animal fat and shortening.
Unsaturated fatty acids, on the other hand, tend to be liquid at room temperature. For example, monounsaturated fats include olive and canola oils, polyunsaturated fats include safflower, sesame and corn oils.
Trans fatty acids occur in food as a result of a process called “hydrogenation.” This produces qualities that are desirable in food manufacturing like a higher melting point and a longer shelf life. Trans fats are generally found in commercial baked goods, deep-fried foods, margarines and packaged snack foods.
During digestion, fat is broken down into fatty acids and then absorbed into the body. They are transported in the blood attached to lipoproteins and delivered to cells. Fatty acids are then used for a variety of functions: providing energy, maintaining cell membranes, and insulating and protecting cells.
Lipids are efficient sources of energy because they provide more than double the number of calories than carbohydrates or proteins (nine calories per one gram of fat). Any excess lipids are then stored in fat cells for future use.
Carbohydrates, proteins and fats are all important macronutrients for our bodies. Because they are the main sources of fuel for the body, it is important to eat a balanced diet that contains all three nutrients. In addition to protein, fat and carbohydrate, our bodies need vitamins and minerals to function properly. The following section provides an overview of these “micronutrients.”
Micronutrients, literally meaning “small nutrients,” refer to the vitamins and minerals that are essential for metabolic processes in our bodies. They are needed in minute amounts compared to macronutrients and do not provide energy in the form of calories.
Although it was well known historically that certain foods were necessary to maintain good health, it wasn’t until the early 1900s when “vital-amines” (an amine is a specific chemical compound) were isolated in the laboratory. Since then, scientists have discovered many more of these vitamins (the –e was dropped since it’s turned out that not all of them are amines) that seem to be critical for human health. Vitamins are either water-soluble or fat-soluble, which merely signifies how the particular vitamin is absorbed into your body, how it’s transported and where it’s stored.
Water-soluble vitamins include all B vitamins (thiamin, riboflavin, niacin, B6, B12), vitamin C and folate. They are essential for many metabolic processes to occur (see micronutrient chart for specific functions). By definition, water-soluble vitamins can exist freely in water so once food is digested, they are absorbed right into the blood and transported to cells throughout the body. If there’s too much of the vitamin in your blood, it gets filtered out by your kidney and excreted from your body. Water-soluble vitamins are not stored in your body so toxicity or “overdosing” is rare.
|B1 (thiamin)||Carbohydrate metabolism||Pork, grains, wheat germ, liver|
|B2 (riboflavin)||Protein metabolism||Meat, milk, liver, kidney|
|Niacin||Carbohydrate, protein and fat metabolism||Protein, peanuts|
|B6 (pyridoxine)||Protein metabolism||Meat, wheat, corn, yeast, pork, liver|
|B12 (cyanocobalamin)||Protein synthesis; forms red blood cells||Meat, milk, liver|
|C (ascorbic acid)||Collagen production; wound healing; helps with iron absorption||Citrus fruits, dark green and yellow vegetables|
|Folate||DNA synthesis; forms red blood cells in bone marrow||Green leafy vegetables, citrus fruits, liver, kidney|
Vitamins A, D, E and K are called fat-soluble vitamins because they cannot exist freely in water (just as oil and water don’t mix). After digestion, they are first absorbed into your lymph system (part of your immune system) and then transported to the circulatory system (blood). Unlike water-soluble vitamins, fat-soluble vitamins require certain carrier proteins (lipoproteins) for transport in the blood to various parts of your body. They are then stored in adipose (fat) cells throughout your body and utilized when needed. Because fat-soluble vitamins are stored and not excreted immediately, consuming excessive doses may lead to toxicity. Fat-soluble vitamins are essential for eye and bone health and blood clotting (see micronutrient chart).
|A||Maintains skin and
|Orange colored vegetables (carrots, pumpkin, sweet potato), dark green leafy vegetables, liver, fortified milk|
|D||Regulates calcium and phosphorous metabolism for bone health||Sunlight, egg yolk, fortified milk|
|E||Antioxidant, protects red blood cells||Fortified cereals, nuts (especially almonds), vegetable oils, whole grains, green vegetables|
|K||Essential for blood clotting||Spinach, kale, green leafy vegetables; also synthesized in our lower intestinal tract|
In addition to vitamins, minerals are necessary for many metabolic processes. Major minerals that are found in large quantities (100 to 1,100 mg) in our bodies include calcium, phosphorous, sodium and potassium. Trace minerals, on the other hand, are found only in minute quantities (0.02 to 3 mg) and include iron, zinc, copper, iodine and selenium.
|Calcium||Bone mineralization, cardiac function, nerve transmission||Dairy products (milk, cheese), legumes, fish, leafy green vegetables, soy beverages, tofu, fortified cereals|
|Phosphorous||Bone mineralization, DNA and RNA synthesis, energy metabolism||Meat, poultry, fish, eggs, dairy products|
|Sodium||Fluid and electrolyte balance||Salt, processed food|
|Potassium||Fluid and electrolyte balance||Fruits and vegetables, legumes, yogurt, fish|
|Iron||Hemoglobin synthesis for oxygen transport||Meats, poultry, clams, oysters, beans, enriched breads and cereals|
Now that you have a general idea of the function and metabolism of these macronutrients, assess your body mass index (BMI) and find some tips on how to incorporate good nutrition habits into your daily lifestyle.
Note: This information is not intended to take the place of advice from a health professional. Check with your physician before starting any diet or exercise program. While all efforts have been made to ensure the information included in this material is correct, new research is released frequently and may invalidate certain pieces of data. 3/07.