CARBOHYDRATES
Carbohydrates provide energy for the human body and are actually the primary source of energy. Carbohydrates are the least expensive and most abundant of all the energy nutrients. Foods rich in carbohydrates grow easily in most climates. They are generally easy to digest. Carbohydrates provide the major source of energy for people all over the world. Carbohydrates provide half of the Kcal for people living in the United States. In some parts of the world where fats and proteins are very scarce and expensive, carbohydrates provide as much as 80% to 100% of Kcal. Carbohydrates are named for the chemical elements that they are made of – carbon, hydrogen, and oxygen.
CLASSIFICATIONS
Carbohydrates are divided into three groups: monosaccharide, disaccharides, and polysaccharides.
Monosaccharides are also called, simple sugars and are the simplest form of carbohydrates. They are sweet and require no digestion, and can be absorbed directly into the bloodstream from the small intestine. These include glucose, fructose, and galactose. Glucose is also called dextrose. It is the form of carbohydrate that all the other forms are converted for metabolism. Dextrose is found naturally in corn syrup, honey, molasses, sweet fruits and some vegetables. Fructose, which is also called levulose and fruit sugar, is found with glucose in many fruits and vegetables, and in honey. Galactose is a product of the digestion of milk and is not found naturally.
Disaccharides are sometimes called double sugars. They Are sweet and must be changed to simple sugars by hydrolysis before they can be absorbed. Disaccharides include sucrose, maltose (often put into beer, baby formula and breakfast foods), andlactose. Sucrose is the form of carbohydrate present in granulated, powdered, brown sugar, and molasses. It is one of the sweetest and cheapest sugars. Its sources are sugar cane, sugar beets, and the sap from maple trees. Maltose is an intermediate product in the digestion of starch within the body. It is manufactured from starch by enzyme action and it is not found naturally and it is not as sweet as glucose or sucrose.
Lactose is the sugar found in milk. It helps the body to absorb calcium. It is different than most of the other sugars because it is not found in plants. It is less sweet than the other single or double sugars.
Polysaccharides are compounds of monosaccharides. Polysaccharides are often called “complex carbohydrates”. Their solubility and digestibility vary. The polysaccharides include starch, dextrins, cellulose, and glycogen.
Starch is a polysaccharide found in grains and vegetables. Vegetables contain less starch because they have higher moisture content. The starch in grain is found mainly in the endosperm or the center part of the grain. This is the part which the white flour is made. The tough outer grain is called the bran. The germ is the smallest part of the cereal grain and is rich in vitamin B complex, vitamin E, minerals, and protein.
Before the starch in grain can be used it must be broken down. The heat and moisture of the cooking break down the outer covering, making it more flavorful and more digestible. Bran itself is indigestible, but it is important that some bran is included in ones diet because of the fiber it provides.
Dextrins are digestible polysaccharides that are the intermediate product of the hydrolysis of starch by enzymes or cooking.
Glycogen is sometimes called “animal starch” because it is the form in which carbohydrates are stored in the body. In the average, healthy adult there is approximately a 12 – 24 hour supply of energy stored in the liver and muscles as glycogen. Glycogen is converted back to glucose when the body needs fuel for energy.
Cellulose is a fibrous form of carbohydrates that makes up the framework of plants. Humans cannot digest cellulose and therefore it has no energy value. Its use is because it absorbs water as it passes along the digestive tract, thus providing bulk for stool and
This prevents constipation. The major sources of cellulose are bra, whole grain cereals and fruits and vegetables. Highly processed or refined foods contain little cellulose because it is removed during processing. Highly processed and refined foods also do not take away our hunger as well.
FUNCTIONS
Providing energy and heat is the major function of carbohydrates. Each gram of carbohydrate provides 4 Kcal (17 kj). When carbohydrates provide energy, they spare proteins for another essential use. The other essential uses are the building and repairing of body tissues. This function is called the protein sparing action of carbohydrates. Carbohydrates are also essential for metabolizing fats.
DIGESTION AND ABSORPTION
Monosaccharides, glucose, fructose and galactose, or the simple sugars can be absorbed from the intestine directly into the bloodstream. They are then carried to the liver where fructose and galactose are changed into glucose. The blood then carries the glucose to the cells.
The disaccharides, sucrose, maltose, and lactose, need an additional step of digestion. They must first be converted to glucose, before they can be absorbed into the bloodstream. This is done by the enzymes, sucrase, maltase, and lactase.
Polysaccharides are more complex and their digestion varies. After the cellulose wall is broken down, starch is changed to an intermediate product, dextrin. It is then changed to maltose and finally, glucose. Cooking can also change starch to dextrin.
The digestion of starch begins in the mouth where the enzyme, ptyalin begins to change starch into dextrin. The next step takes place in the stomach where the food is mixed with gastric juices. Finally, it is in the small intestine where the digestible carbohydrates are changed to simple sugars by enzyme action and then absorbed by the blood.
METABOLISM AND ELIMINATION
All carbohydrates are changed into the simple sugar, glucose before metabolism can take place in the cells. After glucose has been carried to the cells, it can be oxidized. Sometimes, the volume of glucose that reaches the cells exceeds the amount the cells can use. Then some of the glucose is then converted to glycogen and is stored in the liver and the muscles. When the intake exceeds the need, it is then converted to fat and stored as adipose tissue or fat.
The process of glucose metabolism is mainly controlled by the hormone insulin, which is secreted by the islets of Langerhans in the pancreas. When insulin secretion is impaired or absent, the glucose level in the blood becomes excessively high. This is called hyperglycemia and is usually a symptom of diabetes mellitus. In cases such as these a hypoglycemic agent stimulating the production of insulin or insulin must be provided. The diabetics’ intake of carbohydrates must be controlled to balance the insulin. When blood glucose levels are unusually low, this is called hypoglycemia. A mild form can occur if one waits too long between meals or because the pancreas secretes too much insulin.
Oxidation of glucose results in heat and energy. With the exception of cellulose, the only waste products of carbohydrate metabolism are carbon dioxide and water, making carbohydrates a very efficient nutrient. However; even too much of a good thing can add fat.
DIETARY REQUIREMENTS
The Food and Nutrition Board of the National Research Council recommends that people have at least 100 grams of digestible carbohydrate every day. It is estimated that most Americans eat a minimum of 200 grams every day. A diet seriously deficient in carbohydrate can cause ketosis, which is an excessive breakdown of tissue protein and dehydration. Too many carbohydrates can cause tooth decay, gas in the colon and irritation of the lining of the stomach. A deficiency of carbohydrates can result in weight loss and possibly a metabolic problem.
LIPIDS Lipids which are also called fats are oily substances that are not soluble in water. They are soluble in some solvents, such as ether and alcohol. Lipids provide a more concentrated form of energy than carbohydrates. Each gram of fat or lipids contains nine kilocalories. This is more than twice the number as carbohydrates or proteins. Lipids are made up of carbon, hydrogen, and oxygen, just like carbohydrates, but with a much lower proportion of oxygen
FUNCTIONS
Lipids provide energy and heat, but they are also essential for the functioning and structure of body tissues. Fats are a necessary part of cell membranes. They act as carrier’s f essential fatty acids and fat soluble vitamins (A, D, E, and K). The fat stored in our body tissues provides energy when one is unable to eat (today, during illness and long ago during winter or famines). Adipose tissue protects organs and bones from injury by serving as a protective padding and support. It also serves as insulation from the cold. Fats also make us feel full or satisfied after meals. Fat gives flavor to our other foods and slows the rate of digestion, which staves off hunger.
Lipid deficiency is rare in the United States. When a severe deficiency does occur eczema may develop (inflamed and scaly skin). Growth may also be retarded and weight loss may occur when diets are grossly deficient in fats.
FOOD SOURCES
Fats can be found in both plant and animal foods. Animal fats include: fatty meats such as bacon or sausage, lard, butter, cheese, cream, whole milk, and egg yolks. The richest sources of fats in plant food include: cooking oils made from sunflower, safflower, or sesame seeds, or from corn, peanuts, soybeans, olives, or coconut. Nuts, avocados, and chocolate also contain fats. (Especially milk chocolates-dark chocolates are much lower in fats).
CLASSIFICATION
The components of dietary fats are fatty acids and glycerol. While there several fatty acids that the body needs; only linoleic acid is considered essential to our diet. Sources of linoleic acid are corn, sunflower, and safflower oil. The other fatty acids can be synthesized by the body. Most natural fats are combined with glycerol and are called triglycerides.
Fats are generally classified as being saturated, monounsaturated, or polyunsaturated. This depends upon the hydrogen content of the fatty acids that predominate their makeup.
When a fatty acid is saturated, each of its carbon atoms carries all the hydrogen atoms possible. Generally, animal foods contain more saturated fatty acids than unsaturated. These would include: meat, poultry, egg yolks, whole milk, whole milk cheeses, cream, ice cream and butter. While it is true that plant foods generally contain more polyunsaturated fatty acids than saturated fatty acids, there are two exceptions, they are chocolate and coconut. They contain large amounts of saturated fatty acids. Foods that contain a large amount of saturated fats are usually solid at room temperature.
If a fat is monounsaturated, there is one place among the carbon atoms of its fatty acids where there are fewer hydrogen atoms attached than in saturated fats. Foods containing monounsaturated fats are olive oil, avocados, and cashew nuts.
If a fat is polyunsaturated, there are two or more places among the carbon atoms of its fatty acids where there are fewer hydrogen atoms attached than in saturated fats. These foods include: vegetable oils, soft margarines whose major ingredient is liquid vegetable oil, mayonnaise, fish, and peanuts. Foods high in polyunsaturated fats are usually soft or oily.
Hydrogenated fats are polyunsaturated vegetable oils that hydrogen has been added commercially to make them resemble butter. The process is called hydrogenation and it turns polyunsaturated vegetable oils into saturated fats. (Ex: margarine).
DIETARY REQUIREMENTS
There is no daily dietary requirement for fats. The American Heart Association recommends that people reduce fat intake from the current average of 40 to 45 percent of total kcal to 30 to 35 percent. This would reduce the amount of saturated fats and cholesterol in ones diet. Excessive fat in ones diet can lead to obesity and/or heart disease. There are also studies that indicate an association between high fat diets and cancers of the colon, breast, and uterus.
PROTEINS
Body cells are constantly wearing out and in need of replacement. Out of the six nutrient groups, only proteins can make new cells and rebuild tissue. Proteins are the basic material of every body cell. Body protein content is about 18% of the average adults’ body weight. Adequate protein intake is essential for normal growth and development and for the maintenance of health. The word protein is of Greek origin and means “of first importance”.
Just as carbohydrates and lipids, proteins also contain carbon, hydrogen, and oxygen, but in different proportions. Proteins additionally contain nitrogen and usually sulfur. Many also contain phosphorus, iron, and copper as well as other mineral elements. Each gram of protein provides 4 kcal (17 kj).
FUNCTIONS
The primary function of proteins is to build and repair body tissues. Proteins are important components of hormones and enzymes. They play major roles in the regulation of the body processes of digestion and metabolism. They can provide energy if and when the supply of carbohydrates and fats is not sufficient.
CLASSIFICATIONS
Proteins are made up of chemical compounds containing nitrogen that are known as amino acids. These amino acids are sometimes called the building blocks of proteins. Scientists have identified 22 amino acids but found only nine of them to be essential to humans. An essential amino acid is one that is necessary for normal growth and development and must be in ones diet. A nonessential amino acid can be produced by the body if an adequate supply of nitrogen is provided in the diet. Proteins containing essential amino acids are called complete proteins. A complete protein can build and repair tissue.
An incomplete protein lacks one or more essential amino acid and therefore; cannot build tissue without the help of other proteins. If one eats more than one incomplete protein at the same meal they may combine to provide the essential amino acid that is missing in the other. A combination may therefore; provide all nine essential amino acids.
FOOD SOURCES OF PROTEINS
Proteins are found in both plant and animal foods. Animal food sources provide the highest quality, or complete proteins. These include meats, fish, poultry, eggs, milk, and cheese. Proteins found in plant foods are incomplete proteins and are of lower quality. Even though this is true, plant foods are very important sources of protein. Examples of plant foods containing protein are corn, grains, nuts, sunflower seeds, sesame seeds, and legumes such as soy beans, navy beans, pinto beans, split peas, chick peas, and peanuts.
Plant proteins can be used to make textured protein products called analogs. These products are made by extracting the protein from plants (usually soy beans), and spinning it into fibers of nearly pure protein. The fibers are colored, flavored, and shaped into a product that resembles and tastes like meat. It increases the protein content of the food to which it’s added and can also be used as an economical meat replacement.
DIGESTION AND ABSORPTION
The mechanical digestion of protein begins in the mouth where the teeth grind the food into small pieces. Chemical digestion begins in the stomach. Hydrochloric acid prepares the stomach so the enzyme pepsin can begin its task of reducing proteins to polypeptides or partially digested proteins. After the polypeptides reach the small intestine, three pancreatic enzymes (trypsin, chymotrypsin, and carboxypeptidase) continue chemical digestion. Intestinal peptidases reduce the proteins to amino acids. After digestion, the amino acids in the small intestine are absorbed by the blood and carries to a;; body tissues.
METABOLISM AND ELIMINATION
All essential amino acids must be present to build and repair the cells needed. Surplus amino acids are sent back to the liver where they are broken down by splitting off the nitrogen. The remaining parts are used for energy or converted to carbohydrate or fat or stored as glycogen or adipose tissue. The end products of the metabolism of amino acids are carbon dioxide, water, and nitrogen. The excess nitrogen is sent to the kidneys and excreted in urea. Urea is the main end product of human protein metabolism.
PROTEIN REQUIREMENTS
One’s protein requirement is determined by size, age, sex, and physical and emotional conditions. A large person has more body cells to maintain than a small person…etc….If digestion is inefficient, fewer amino acids are absorbed by the body, thus raising the protein requirement. Extra protein is usually required after surgery, severe burns, or during infections to replace lost tissue and manufacture antibodies. Emotional trauma may cause the body to excrete more nitrogen than it normally does, thus increasing the need for protein.
The National Research Council of the National Academy of Sciences considers the average adult’s daily requirement to be 0.8 grams of protein per kilogram of body weight.
PROTEIN DEFICIENCY
When a person is unable to obtain adequate protein for an extended period of time, muscle wasting will occur and arms and legs become very thin. At the same time, nutritional edema can develop. Edema is the retention of fluids in the body. This would make the person look swollen. This water is excreted when sufficient protein is eaten. When one is deficient in protein, one may lose appetite, strength, and weight. Wounds may also heal very slowly. Patients suffering from nutritional edema often become lethargic and depressed. This can be seen in grossly neglected children, the elderly poor or incapacitated. This is not something that is common in the United States. There are diseases caused by grossly inadequate supplies of protein, but these are most often seen in third world countries where there are long term shortages of both protein and energy foods.
Article by http://www.excellentguide.com | 
