LEARNING OBJECTIVE: Identify the components of good nutrition.
Foods are substances from animal and plant sources that yield heat and energy when ingested and absorbed by the body. Food nutrients build and renew tissues and regulate the body processes. The unit commonly used for describing energy intake and energy expenditure is the calorie. Good food sources contain substantial amounts of nutrients in relation to caloric content and provide upwards of 10 percent of the U.S. Recommended Dietary Allowance for each specific nutrient. Most people can get enough of each required nutrient daily by eating a wide variety of foods.
Proteins are the “building blocks” of the body and provide important required nutritive elements. Proteins are needed for growth, maintenance, and replacement of body cells, and they form hormones and enzymes used to regulate body processes. Extra protein is either used to supply energy or is changed into body fat. Found in both the animal and plant kingdoms, all proteins are composed of amino acids. Some amino acids are absolutely essential to maintain life and are necessary for repair, growth, and body development. Of the approximately 20 amino acids, our body can produce all but nine. These nine amino acids are termed “essential amino acids.” We must get them from food, and we need all nine at one time so our body can use them effectively.
Proteins, which promote tissue growth and renewal, have long been recognized as the main structural unit of all living cells. Each gram (g) of protein yields 4 calories in the process of metabolism. Although proteins yield energy, they are an expensive source. If sufficient carbohydrates are not supplied, the body will use protein for energy requirements. This protein may be obtained from muscle tissue, producing the “wasting effect” of long-term starvation and some diseases.
A constant protein source is required in the daily diet. The normal daily protein intake for adults should be 0.8 gram per kilogram (g/kg) (2.2 lbs) of body weight, or 12 percent of the total caloric intake. Pregnant women require an additional 10 grams of protein a day over the normal daily intake.
Proteins play an important role in recovering from fractures, burns, and infections. They are also important in healing wounds and recovering from surgical procedures. In cases of recovery, protein intake should be increased in accordance with the severity of the condition, and carbohydrates and fats can be added liberally. While proteins can supply energy, they are not a main source of energy like carbohydrates and fat.
Ideally, the patient should receive protein by mouth; however, it is sometimes necessary to meet the minimum requirements parenterally. Glucose parenteral solution, given during an acute emergency period, will prevent some loss of protein. Protein deficiency may stunt growth, promote a secondary anemia, or induce nutritional edema. Dietary sources of protein and the nine essential amino acids are milk, yogurt, eggs, meats, fish, cheese, poultry, peanut butter, legumes, and nuts. Protein from plant sources is best when combined with animal protein, such as milk plus peanut butter, or when legumes are combined with grains, such as Navy beans plus rice.
The chief functions of fats are to supply energy and transport fat-soluble vitamins. Each gram of fat yields 9 calories. Fats provide the most concentrated source of calories (and, therefore, energy) of all the food nutrients. Fats are found in both the animal and vegetable kingdoms. Fatty acids and glycerol are the end products of the digestion of fats.
Many fats act as carriers for the fat-soluble vitamins A, D, E, and K. They also act both as a padding for vital organs, particularly the kidneys, and as subcutaneous tissue to help conserve body heat. Fat is stored as adipose (fatty) tissue to form a reserve supply in time of need. Dietary fats delay gastric emptying and promote a feeling of fullness. Excess calories from fats may produce obesity, the forerunner of arteriosclerosis, hypertension, gallbladder disease, and diabetes. A diet high in fat, especially saturated fat and cholesterol, contributes to elevated blood cholesterol levels in many people. Adults over the age of 30 should have a serum cholesterol level of less than 200 mg/dl. Health experts agree that less than 30 percent of our total calories per day should come from fat. Saturated fat intake should be no more than 10 percent of the total calories.
Reducing dietary fat is also a good way to limit calories. Decreased fat intake results in fewer calories without a reduction of most nutrients. Too little fat in the diet may lead to being underweight, having insufficient padding for the vital organs, and lowered energy. Butter, margarine, cream cheese, fatty meats, whole milk, olives, avocados, egg yolks, nuts, commercial bakery products, and vegetable oils are all sources of dietary fat.
Carbohydrates (sugar and starches) are the most efficient sources of energy and are known as the “fuel of life.” They are abundantly found in most plant food sources. Complex carbohydrates (starches) are in breads, cereals, pasta, rice, dry beans and peas, and other vegetables, such as potatoes and corn. Simple carbohydrates are found in sugars, honey, syrup, jam, and many desserts. The new nutritional guidelines established by the Food and Drug Administration (FDA) recommend that complex carbohydrates and naturally occurring sugars (found primarily in fruit) make up approximately 50 percent of one’s total caloric intake. The FDA also recommends that refined and processed sugars make up no more than 10 percent of the calories in one’s diet.
Each gram of carbohydrate yields 4 calories in the process of its metabolism. Carbohydrates must be reduced to glucose before the body can use them. Carbohydrates are stored in the muscles to fuel their movement, and in the liver as glycogen, which is then broken down and released as glucose at the exact rate needed by the body. This latter mechanism is controlled largely by insulin from the pancreas. During fasting, liver glycogen is rapidly depleted, leading the body to use its fat for energy. Carbohydrates that are not needed for energy are converted to and stored as adipose (fat) tissue.
The main functions of carbohydrates are to
Although mineral elements constitute only a small portion of the total body weight, they enter into the activities of the body to a much greater degree than their weight would indicate. Certain mineral elements are essential for specific body functions. While it is not yet known exactly how many of the mineral elements are indispensable to the body functions, seemingly small changes of mineral concentration can be fatal. These essential inorganic elements contribute overwhelmingly to the skeletal framework of the body and teeth, and they are an essential part of many organic compounds.
Minerals form an integral part of basic cell structure and circulate in body fluids. They also exercise specific physiologic influences on the function of body tissues. For mineral needs to be met satisfactorily, consumption of each element must be sufficient to cover body tissue requirements and to meet changing physiological needs. At one time, it was erroneously believed that any diet adequate in other respects would also provide an adequate intake of essential minerals. This is not so. Foods vary greatly in their mineral—as well as their overall nutritional—content, depending on growing conditions, storage, and preparation procedures. Among the major minerals are calcium, phosphorus, iron, potassium, zinc, and magnesium. Table 9–1 lists the essential elements, the foods that contain them, and their functions.
Vitamins are essential compounds that are present in food in minute quantities. Although vitamins do not furnish energy or act as tissue-building materials, they do act as catalysts in many body chemical reactions and are necessary for normal metabolic functions, growth, and the health of the human body. Their absence results in malnutrition and specific deficiency diseases. Vitamin chemistry is complex and nutritional experimentation is difficult, so our knowledge of them is being continually supplemented and revised. It is quite possible that additional vitamins will be discovered or that some of those already recognized may prove to contain more than one factor.
Vitamins are so widely distributed in food that a properly prepared normal diet usually provides an adequate amount. Vitamins can be destroyed during the preparation or preservation of certain foods; however, manufacturers frequently add vitamins to their products to replace those destroyed or removed in processing. Since fat-soluble vitamins can be stored in the body, it is possible to develop hypervitaminosis by consuming excessive amounts of these nutrients, and death may result in extreme cases. Fat-soluble vitamins include A, D, E, and K.
Table 9–1.—Mineral Elements in Nutrition
|Element||Rich Sources||Function in the Body|
|Iodine||Seafood, water, and plant life in nongoiterous regions,
and iodized salt
|Assists in normal functioning of the thyroid gland.|
|Sodium||Table salt, seafood, animal products, and foods
processed with sodium
|Regulates osmotic pressure, pH balance, and heartbeat.|
|Potassium||Avocados, bananas, oranges, potatoes, tomatoes,
nuts, meat, coffee, tea, milk, and molasses
|Regulates osmotic pressure and pH balance.
A constituent of all cells.
|Magnesium||Nuts, whole-grain cereals, legumes, and vegetables||Assists in maintaining mineral balance.|
|Calcium||Milk, yogurt, cheese, some green vegetables,
molasses, sardines, and salmon
|Assists in blood coagulation; regulates heartbeat, aids in
regulating mineral metabolism and muscle and nerve response.
A constituent of bones and teeth.
|Phosphorus||Milk, yogurt, poultry, fish, meats, cheese, nuts,
cereals, and legumes
|Aids in metabolizing organic foodstuffs and maintains
pH balance. A constituent of bones and teeth.
|Iron||Liver, egg yolks, oyster, legumes, whole or fortified
grains, dark and green vegetables, and dried fruit
|Helps carry oxygen throughout the body. A constituent
of hemoglobin, blood, and tissue.
|Chlorine||Table salt, seafoods, and animal products||Regulates osmotic pressure. A constituent of gastric acid.|
|Sulphur||Protein foods||Promotes hair and nail formation and growth.
A constituent of all body tissue.
|Copper||Liver, kidney, nuts, dried legumes, some shellfish,
|Aids in the use of iron in hemoglobin synthesis.|
|Zinc||Meat, liver, eggs, seafood (especially oysters),
milk, and whole-grain products
|Regulates growth, taste acuity, and appetite.
A constituent of enzymes.
Water-soluble vitamins, such as vitamin C and the B-complex vitamins, are not stored in the body to any great extent. Rather, they are used as necessary by the body, and any amounts that remain are excreted in the urine. As a result, these vitamins must be replenished daily to ensure optimum health.
VITAMIN AND MINERAL SUPPLEMENTS
Vitamin supplements are usually not necessary if a diet includes a wide variety of foods. Exceptions may occur in prenatal diets in which iron is low, as well as in patients who are deficient in a specific vitamin. Vitamin supplements should be taken only on a physician or dietitian’s recommendation.
Vitamin and mineral supplements are being widely used by physically active people because of all the performance-enhancing claims made by supplement manufacturers. It is estimated that 40–50 percent of athletes use some form of vitamin/mineral supplements. Some doses range from amounts similar to the Recommended Dietary Allowances (RDA) up to levels many times the RDA. Supplements are useful under a variety of conditions, such as if an individual:
Often, laxatives are prescribed in conjunction with some medical treatments and may cause decreased absorption of vitamins, loss of minerals and elec- trolytes, or inhibition of glucose uptake. Therefore, any patient on laxatives should be carefully monitored, and supplementary nutritives should be administered as necessary.
Taking a general multivitamin supplement appears to be without measurable performance enhancing effects in healthy, well-nourished, physically active personnel. Similarly, no improvements in muscle strength or endurance have been noted in strength athletes, such as body builders, who tend to use megadoses of vitamin and mineral supplements. The indiscriminate use of high-potency vitamins and minerals is of growing concern since excessive amounts of vitamins and/or minerals can be harmful and may result in nutrient imbalances. Excessive intake of some vitamin and mineral supplements can result in adverse—and possibly toxic–side effects.
Water is often called the “forgotten nutrient.” Water is needed to replace body fluids lost primarily in urine and sweat. A person can survive weeks without food but only days without water. Water makes up 70 percent of body weight and is found in every cell in the body. It is the medium through which nutrients are transported from the digestive tract to the cells where they are needed. Water is also the medium through which the by-products of cell metabolism are removed.
Water also serves as the medium in which the chemical processes of life take place. It is normally taken into the body in beverages, soups, and in the form of solid foods. Fluid needs are increased with sweating, vomiting, diarrhea, high-protein diets, and in hot environments. An insufficient intake may cause dehydration, evidenced by loss of weight, increased body temperature, and dizziness.