Nutrition
Nutrition
Nutrition is the means by which organisms obtain and use nutrients. Nutrition is also the determination of the kinds and quantities of substances (nutrients) needed by organisms to sustain life. Some organisms such as plants require only a supply of light, water, and a few other molecules and ions in order to thrive, and are known as autotrophs, or self nourishers, for they literally build their own molecules and capture energy in the process. There are a few other non-plant autotrophic organisms in the deep oceans near geothermal vents that are able to build their own nutrients without using sunlight.
While green plants get the energy they need directly from sunlight, animals must get the energy that they need for life functions from plants.
The major types of molecules found in organisms are water, carbohydrates, proteins, lipids, and nucleic acids.
Proteins are large molecules built from different combinations of large numbers of amino acids. Of the 20 different amino acids that make up our body’s proteins, we can build 12 from other foods, but there are eight amino acids that humans also need and which they cannot make, called essential amino acids. One of the eight essential amino acids (methio-nine) is found in corn, but not in beans, and two others (lysine and tryptophan) are found in beans, but in only small amounts in corn. Therefore, the combination of beans and corn, found in many Mexican foods, supplies a balance of the essential amino acids.
In 2005, the Food Pyramid was redesigned to provide more personalized nutritional guidelines for children and adults. The redesigned pyramid also considers gender, physical activity level, exercise guidelines, and food safety. A personalized food pyramid can be built by visiting the United States Department of Agriculture’s “My Food Pyramid” website at <http://www.mypyramid.gov/mypyramid/index.aspx>
The first section of the Food Pyramid, one of two parts with the greatest volume, consists of grains: bread, pasta, cereals, and rice. This food group, mostly carbohydrates, should provide most of the food energy needed. The recommendations are given in servings. A serving varies from food to food, but is in the range of 1-2 oz (30-60 g) per serving. Depending on physical size, age, gender, and activity, 6–11 servings per day are recommended from the cereal group. Grains are divided into two sub-groups, whole-grains and refined grains. At least half of grain servings should be from whole grains.
The second level of the food pyramid consists of vegetables, which are divided into five sub-groups. These are especially important in supplying micronutrients. Micronutrients are elements that help regulate physiological pathways. A second benefit derived from this group comes from indigestible fiber, which is correlated with better functioning and health of the large intestine. Basic recommendations call for eating 1-3 cups of vegetables per day, based on age and gender. Eating more dark green vegetables, orange vegetables, and dry peas and beans are also recommended.
The pyramid’s third level consists of fruit, which has now been separated from the vegetable group. One to two cups of fruit are recommended per day, according to variables of age and gender. The pyramid also contains a suggestion to go light on fruit juices, instead giving whole fruits preference.
The two protein groups in the pyramid are the milk group and the meat group. The milk group also includes cheese and yogurt. The meat group includes proteins in the form of meats, eggs, beans, and nuts. The major function of proteins is to repair or build new tissue and to supply enzymes and hormones Serving suggestions vary according to age, gender, and physical activity, but fall within 1-6.5 ounces of meat protein per day and 2-3 cups from the milk group per day. The pyramid also recommends nuts, especially sunflower seeds, almonds, or hazelnuts as good sources for vitamin E.
The smallest section of the pyramid contains the lipids, demonstrating that fats and oils should be consumed in small quantities for optimum health. Vegetable oils or fat from nuts or fish is recommended over animal fat. In addition, as of January 1, 2006, food manufacturers are required to list the total amount of trans fatty acids, also known as “trans fats” on food labels. Trans fatty acids are mainly found in baked goods, margarines, snack foods, fried foods, and salad dressings. Diets high in trans fats have a proven link with elevated levels of LDL (“bad”) cholesterol in the blood.
Minerals and trace elements
Micronutrients are subdivided according to the quantities needed in the human diet. If more than 100 milligrams (mg) per day of an element is needed
KEY TERMS
Anion —A negatively charged ion (i.e., Cl-).
ATP —Adenosine triphosphate; a high energy molecule that cells use to drive energy-requiring processes such as biosynthesis, transport, growth, and movement.
Carbohydrates —Compounds that contain carbon, hydrogen, and oxygen. The ratio of carbon to oxygen is about one to one. Examples are sugar, starch, and cellulose.
Electrolyte —Compounds that ionize in a solution; electrolytes dissolved in the blood play an important role in maintaining the proper functioning of the body.
FAD —Flavin-Adenine Dinucleotide.
Gluconate, lactate, etc. —These terms refer to the anionic components of organic salts. For example, a positive potassium ion can be balanced in an electrolyte with a gluconate anion. If the liquid part were to be evaporated, the residue would be crystalline, potassium gluconate salt.
Life processes —Term referring to activities such as metabolism, cell division, excretion, and movement.
Lipids —Molecules in this group are made of the same elements as carbohydrates, but in lipids there is much more carbon than oxygen. Examples are fats, oils, and cholesterol.
Nucleic acids —This is a generic term including both RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). The DNA encodes genetic information and the RNA molecules use it to direct protein building.
Nucleotide —Molecular units that make up the nucleic acids. Each is composed of a nitrogen base, a sugar, and a phosphate group.
Oxidation —A biochemical process which is part of metabolism. It involves the steady but relatively slow release of energy from food molecules for cell activity.
Proteins —Large molecules built from long chains of smaller molecules, the amino acids. Nitrogen is an element in protein in addition to the carbon, hydrogen, and oxygen found in major food molecules. The tough flexible parts of an animal such as skin, cartilage, and muscle are mostly protein.
(for an adult), it is classed as a mineral. The seven essential minerals are calcium, magnesium, phosphorus, sodium, potassium, sulfur, and chlorine. Substances that are essential but needed in amounts of less than 100 mg per day are called trace elements. These are iron, copper, iodine, manganese, zinc, molybdenum, selenium, and chromium. There are likely others (such as boron) that are yet to be identified.
Calcium and phosphorus are both used structurally to form bones and teeth. Lesser known but vital functions of calcium include its uses as an enzyme activator and as a regulator of nerve and muscle activity. Phosphorous is also a component of nucleotide molecules that are structural components of the nucleic acids, DNA and RNA, and of the energy transfer molecules such as ATP, NAD, and FAD.
Magnesium is found in bones too, but, more importantly, it is needed in adequate amounts to work with calcium in regulating nerve and muscle activity. In fact, an early symptom of magnesium shortage can be irregular heart action. Sodium is necessary for the proper functioning of the nerves and muscles. Sodium is more concentrated in the fluids outside of the cells than the intraocular fluids. Sodium is more often consumed in excess because it is easy to enhance the flavors of foods by adding table salt (sodium chloride). Potassium ions are most concentrated in the fluid inside cells. There is evidence that high blood pressure can be prevented or controlled by increasing one’s intake of potassium. Chloride functions as an electrolyte balance for the sodium and other positive ions in cell and tissue fluids and is necessary for the salivary enzyme ptyalin to help digest starch. Sulfur is a component of three amino acids and is part of the enzyme molecules active in the oxidation of fatty acids.
These minerals must be in their ionic form so as to be soluble and absorbable. Many minerals are often chelated, that is, attached to a larger organic particle such as an amino acid, or anions such as gluconate, lactate, or citrate to be properly observed. Some trace elements function in cooperation with an enzyme or a vitamin molecule to bring about physiological responses.
More and more, people are choosing foods for their vitamin or mineral content, because the foods provide specific nutrients that may otherwise be missing. Adding daily supplements of vitamins C, E, and A (or its precursor beta carotene) to diets may promote good health and fight disease.
See also Vitamin.
Resources
BOOKS
Willett, Walter, and Skerrett, P.J. Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating. New York: Free Press, 2005.
OTHER
United States Department of Agriculture. “Dietary Guideline for Americans 2005.” <http://www.health.gov/dietaryguidelines/dga2005/document/> (accessed on December 3, 2006).
Chester VanderZee