Since the days of prehistoric hunters and gathers, people have understood that some animals and plants are good to eat and others are not. For thousands of years, cultures worldwide have attributed medicinal or beneficial effects to certain foods, particularly plants, and have recognized that foods that would otherwise be fine to eat may be unhealthy if improperly prepared or stored. But not until the past few decades have people become increasingly concerned about understanding how all foods affect their health and what foods can and should be consumed in order to promote good health. These concerns compose the study of nutrition. Nutrition is the science that studies nutrients (chemical substances found in food) that nourish the body by promoting growth, maintenance and repair and by facilitating body functions. Some nutrients also provide energy. The six categories of nutrients are carbohydrates, fats, proteins, vitamins, minerals and water. Essential nutrients are those that must be provided by food because the body does not produce them in sufficient quantities or cannot make them at all. Some nutritional components are considered nonessential because healthy, well-nourished bodies can make them in sufficient quantities to satisfy their needs. Our bodies depend upon the various nutrients for different purposes and require different amounts of each depending on age, sex and health. In addition, some nutrients depend on one another for proper functioning. For example, calcium and vitamin D work together in the body: Vitamin D promotes the absorption of the calcium that the body utilizes for proper bone growth. Because foods differ with regard to their nutritional content, it is important to eat a variety of foods in order to achieve a proper nutritional balance. Essential Nutrients Three of the essential nutrients provide calories or energy. Sometimes referred to as macronutrients, they are carbohydrates, fats and proteins. A calorie (abbreviated kcal) is the way we describe the amount of energy in food. The number of calories in a food is measured by a device called a calorimeter, which burns the food and measures the heat the food gives off. From that measurement, an estimate for how the food would be burned in the body is calculated. The results of that calculation are the calorie designations assigned to the energy nutrients. One gram of pure fat supplies 9 kcal; one gram of pure carbohydrate supplies 4 kcal, as does one gram of pure protein. Most foods are a combination of carbohydrates, proteins and fats; their kcal content may not be easily determined unless we know how much of each nutrient the food contains. Vitamins and minerals are essential nutrients and must be provided through the diet because the body cannot manufacture them in quantities adequate to ensure good health. They have no calories. Because they are needed in smaller amounts than the other nutrients, they are sometimes referred to as the micronutrients. Carbohydrates Carbohydrates comprise carbon, hydrogen and oxygen and are found exclusively in plant foods and milk sugars. Simple carbohydrates include monosaccharides (single sugars) and disaccharides (double sugars). Simple carbohydrates are found in the naturally occurring sugars in fruit, vegetables and milk, as well as sweeteners such as honey, corn syrup and table sugar. Complex carbohydrates are composed of long chains of the monosaccharide glucose. Starch is a complex carbohydrate. Complex carbohydrates are found in vegetables, fruits and cereal grains such as wheat, barley and oats. The body digests (or breaks down) these sugars and starches into glucose. Glucose, also known as blood sugar, is a very important source of energy for the body. Another complex carbohydrate is fiber. Fiber is a unique carbohydrate because humans cannot digest it, so they do not derive calories from it. Dietary fiber, which generally comes from the seeds and cell walls of fruits, vegetables and cereal grains, plays an important role in health. Because the body cannot digest dietary fiber, it passes through the digestive system almost completely unchanged. This helps keep the digestive tract running smoothly. Fiber increases fecal hulk, which encourages proper elimination of waste products from the large intestines and helps avoid some forms of gastrointestinal distress. Some forms of fiber also reduce serum cholesterol. Fats Fats, like carbohydrates, are composed of carbon, hydrogen and oxygen. The differences between carbohydrates and fats are the number and arrangement of the carbon, hydrogen and oxygen atoms. Fats are found in both animal and plant foods, although fruits contain very little fat. Fats provide calories, help carry fat-soluble vitamins and give food a creamy, pleasant mouthfeel. Depending upon their structure, the fats in foods can be classified as saturated, monounsaturated or polyunsaturated. Most foods contain a combination of the three, although one kind may predominate. If saturated fat is the most abundant kind (as in the fat surrounding muscle meats), we describe the food as being saturated even though it contains a mixture of all three fats. Saturated fats are found mainly in animal products such as milk, eggs and meats, as well as in tropical oils such as coconut and palm. Monounsaturated fats come primarily from plants and plant foods such as avocados and olives and the oils made from them. Polyunsaturated fats come from plants (soy and corn, for example) and fish. Vegetable oils like rapeseed (canola) and olive are high in monounsaturated fat. Cottonseed, sunflower, corn and safflower oils are high in polyunsaturated fat. All oils, however, are a combination of the three kinds of fat. Saturated fats such as butter, lard and other animal fats are usually solid at room temperature. Monounsaturated and polyunsaturated fats are usually liquid at room temperature. Hydrogenation is a process by which a liquid fat is made more solid (or saturated) by the addition of hydrogen atoms. Hydrogenation increases the percentage of saturated fatty acids, resulting in a more solid product (such as margarine made from a polyunsaturated oil like corn oil). It also reduces the tendency to rancidity so shelf life is increased. The body has more difficulty breaking down saturated fats than it does monounsaturated and polyunsaturated fats. Research suggests that high-fat diets, especially diets high in saturated fat, may be linked to heart disease, obesity and certain forms of cancer. Saturated fats are also linked to high levels of blood cholesterol, which are associated with arteriosclerosis (hardening of the arteries). Although the liver can produce all the cholesterol the body needs, additional cholesterol is often provided in the diet. Dietary cholesterol is found only in foods of animal origin. Meats, poultry, fish, shellfish, eggs and dairy products are all sources of dietary cholesterol. Fruits, vegetables and grains are cholesterol free. Minerals Minerals cannot be manufactured by the body. They are obtained by eating plants that have drawn minerals from the ground or the flesh of animals that have eaten such plants. Minerals are a critical component in hard and soft tissues (for example, the calcium, magnesium and phosphorus present in bones and teeth). Minerals also regulate certain necessary body functions. For example, nerve impulses are transmitted through an exchange of sodium and potassium ions in the nerve cells. Minerals are divided into two categories: trace minerals and major minerals. Trace minerals such as iron are needed in only very small amounts. Major minerals such as calcium are needed in relatively larger quantities. As with vitamins, food processing and preparation can reduce a food's mineral content. Soaking or cooking in large amounts of water can leach out small quantities of water-soluble minerals. Processing or refining grains, such as the wheat it used to make white flour also removes minerals. Proteins Proteins are found in both animal and plant foods. They differ from carbohydrates and fats in that they contain nitrogen as well as carbon, hydrogen and oxygen. Protein chains consist of amino acids, the building blocks of protein. There are 20 amino acids, 9 of which are essential. People who eat a varied diet with adequate calories and protein can easily get all the essential amino acids. The specific combination of amino acids gives each protein its unique characteristics and properties. Proteins are necessary for manufacturing, maintaining and repairing body tissues. They are essential for the periodic replacement of the outer layer of skin as well as for blood clotting and scar tissue formation. Hair and nails, which provide a protective cover for the body, are composed of proteins. Another important function of protein is the regulation of body processes. Proteins regulate the balance of water, acids and bases, and move nutrients in and out of cells. Proteins contribute to the immune system by producing antibodies, which are necessary for combating diseases. Proteins also form the enzymes that act as catalysts for body functions and the hormones that help direct body processes. Vitamins Vitamins are vital dietary substances needed to regulate metabolism and for normal growth and body functions. They are essential and noncaloric, and needed in the body in small amounts. There are 13 vitamins. Vitamins are divided into two categories: fat soluble and water-soluble. The fat-soluble vitamins are A, D, F and K and are found in foods containing fat. Excess supplies of these vitamins may be stored in fatty tissues and the liver. Water-soluble vitamins are vitamin C and the B complex vitamins, including: thiamin (B) riboflavin(B) niacin (B) cyano-cobalamin (B12) pyridoxine (B) pantothenic acid biotin folate Vitamins B1 and B2 are commonly referred to by their names, thiamin and riboflavin, respectively; whereas cobalamin and pyridoxine are commonly referred to by their letter designations, B12 and B6, respectively. Water-soluble vitamins are not stored to the extent that fat-soluble vitamins are, and excesses may be excreted in the urine. Because of these differences, deficiencies in water-soluble vitamins usually develop more rapidly. Virtually all foods contain some vitamins. Many factors contribute to a particular food's vitamin concentration: an animal's feed; the manner by which the produce is harvested, stored or processed; even the type of soil, sunlight, rainfall and temperature have significant effects on a food's vitamin content. For example, tomatoes have a higher concentration of vitamin C when picked ripe from the vine than when picked green. Furthermore, different varieties of fruits and vegetables have different vitamin contents. A Wegener apple, for example, has 19 mg of vitamin C, whereas a Red Delicious has only 6 mg. You can control vitamin concentration and retention through careful food Preparation: Try to prepare vegetables as close to service time as possible; vegetables cut long before service lose more vitamins than those cut immediately before cooking. Whether a vegetable is boiled, steamed or microwave also determines the amount of vitamins it retains. Because the B complex vitamins and vitamin C are water soluble, they are easily bleached (washed out) or destroyed by food processing and preparation techniques involving high temperatures and water. Steaming and microwaving help retain nutrients (when steaming, keep the water level below the vegetables). But microwave cooking is best because it cooks vegetables with minimal water in less time. In general, roasting and grilling meats, poultry, fish and shellfish preserve more vitamins than stewing and braising. The temperatures to which foods are cooked and length of time they are cooked may affect vitamin retention as well. Storage affects vitamin concentrations. For example, long exposure to air may destroy vitamin C. Using airtight containers prevents some of this loss. Riboflavin is sensitive to light, so milk products (which are good sources of riboflavin) should he stored in opaque containers. Water The human body is approximately 73% water. Water is necessary for transporting nutrients and wastes throughout the body. It cushions the cells, lubricates the joints, and maintains stable body temperatures and assists waste elimination. It also promotes functioning of the nervous system and muscles. Although the principal sources of water are beverages, water is also the predominant nutrient by weight in most foods. Some foods such as tomatoes, oranges, watermelon and iceberg lettuce are particularly high in water. Others such as dried fruits, nuts and seeds are lower. Water is also formed by the body when other nutrients are metabolized. The average adult should consume at least 8 to 10 glasses (64 fluid ounces or 2 liters) of water a day to ensure adequate intake. People who exercise should replace body water lost through sweat by drinking more. SPECIAL DIETARY NEEDS As we grow older our nutrient needs change. We expect teenage boys, for example, to eat us "out of house and home," but we attribute this habit to their increasing energy requirements, rather then to rising needs for nutrients. In many cases we unconsciously adjust to changes in nutrient requirements. Most people approaching middle age gradually eat less, but it may take a long time before they look back and realize how much their eating patterns have changed. Sometimes we do not adapt our eating habits instinctively: for example, people gain excess weight if they do not reduce their calorie intake to suit lower energy use; and teenagers often use up a large number of calories on soft drinks rather than on foods which would provide them with more nutrients. As our nutrient needs change during particular stages of life, certain foods and eating habits can help us to adjust more effectively. NUTRIENTS NEEDS IN PUBERTY Healthy eating is rarely a priority for young people, yet the growth spurt of children in adolescent years causes a jump in their requirement for most nutrients. This is especially true of calcium and iron, which young people need more than adults because they are using these minerals for rapidly forming extra bone and tissue. Lack of calcium can affect bone growth, which peaks during the mid-teen years. The bone strength laid down at this time can affect the risk of osteoporosis in middle age. Girls often restrict their food intake because they want to be thin, just as puberty is making them curvier. Their iron requirement roughly doubles at puberty as extra needs for growth coincides with the loss of iron during menstruation. Up to a quarter of teenage girls are likely to be iron-deficient, affecting their energy levels, resistance to infection, and, in some cases, academic performance. Many teenage girls become vegetarian and need to take exter care to eat iron-rich foods. Vegetarian leanings often overlap with desire to control weight, and may mask the development of eating disorders such as anorexia. Zinc deficiency, reduces tast and appetite, is thought to play a part in some cases. Boys are increasingly affected by the fashion for thin bodies, with similar risks to their health. The level of sugar eaten by many older children is very high. this increases tooth decay and reduces their cahnces of obtaining a balanced diet. Teaching young people how to put together a balanced diet is important so that they can obtain the nutrients they need without following so many of their parents in becoming overweight. Lack of veriety is often a feature of teenage eating habits, and introducing younger children to as wide a range of foods as possible, especially fresh vegetables and fruits, helps guard against this. SPECIAL VALUE FOODS Eat more often Calcium-rich foods: yogurt, hard cheese, milk, tofu, almonds, green leafy vegetables, sardines. Iron-rich foods: chicken liver, dried apricots, beans, red meat, oily fish, green leafy vegetables. Zinc-rich foods: shellfish, lean meat, pumpkin seeds. Avoid Large amounts of sugary foods are not desirable even for very active teenagers. wheat bran, except in whole-wheat bread. NUTRIENTS NEEDS IN PREGNANCY It is important to eat well for several months before conceiving to build up your nuritional status. Critical developments in fetal nurve and brain development take place in the first 3-4 weeks, a period when most women do not yet know that they are pregnant. Folic acid reduces the risk of neural tube defects and women planning to conceive should take 400mcg folic acid a day until they are 12 weeks pregnant, and eat foods rich in folic acid during their pregnancy. If you are planning a pregnancy, avoid being underweight and give up smoking and alcohol consumption completely. This helps guard against having a low birthweight or premature baby, who has a far higher risk of poor health. During pregnancy, it is more important to improve the quality of your diet than eat more. Although iron needs rise, it is better to eat iron-rich foods than to take iron supplements, unless your homoglobin levels are low. Many pregnant women eat little omega-3 fatty acids, which are critical for fetal development. SPECIAL VALUE FOODS Eat more often Calcium-rich foods: yogurt, hard cheese, milk, tofu, almonds, green leafy vegetables, salad greens, sardines, whitebait. Fiber-rich foods: dried apricots, linseed. Folic acid and iron-rich foods: red meat, cruciferous vegetables, watercress, wheat germ, beans. Omega-3-rich oily fish, linseed. Avoid Pregnant women are advised not to eat liver. Excess retinol vitamin A (but not beta-carotene) can cause fetal abnormalities. Food poisoning carries extra risks. NUTRIENTS NEEDS FOR OLDER PEOPLE As we get older, we need fewer calories but similar amounts of nutrients, so it becomes even more important to choose foods that provide higher levels of nutrients per calorie. The drop in caloric needs is due to a slower metabolism, and in most people, less activity. Keeping active allows older people to eat more food and nutrients without becoming overweight, which increases the risk of joint problems, diabetes, gallstones, and other illnesses. Keeping active also helps prevent depression, poor circulation, and excess bone loss. In many older people , nutrient absorption declines. Levels of zinc and vitamin B6 and D are often low, reducing the body's immunity and general well-being. In the elderly, especially the less active, improving nutrition has shown dramatic benefits, for instance, cutting down the hospital recovery time after surgery, reducing infections, and in some cases helping to reduce mental confusion. SPECIAL VALUE FOODS Eat more often Antioxidant-rich foods: red and orange vegetables and fruits. Digestive stimulants to help absorption: chili peppers, artichokes, watercress. Zinc-rich foods for the immune system: shellfish, pumpkin seeds, chicken liver. Fiber-rich foods: Whole-wheat bread, linseed, sunflower seeds. Oily fish to provide vitamin D and essential fatty acids. Potassium-rich fruits and juices. Avoid Wheat bran, except in whole-wheat bread. Dehydration: drink ample fluid.   COPYRIGHT©2005 VICTORIA PACKING CORP. ALL RIGHTS RESERVED ( PRO-042305-OM )