The human body needs various substances from the environment in order to grow, reproduce, and survive. We breathe air to acquire the oxygen our cells need to survive; we drink water to replenish vital supplies of liquid. And we eat to provide us with all-important energy sources since energy is provided by the body's use of digested protein, fat, and carbohydrate. Other components are also needed, although in much smaller amounts. These include essential amino acids, fatty acids, mineral, trace minerals, and vitamins. All the foods we eat provide some level of nutrition. There may be no one perfect diet for all of us or even for one of us at all times but there are some general principles for food selection to most of us.
Basic components of Food
Water seems so ordinary that you may forget how vital it is to good health. Water plays a important role in nearly every major function of your body. Water regulates body temperature, carries nutrients and oxygen to cells and removes wastes. It also cushions joints and helps protect organs and tissues. Drinking eight, eight-ounce servings of water daily will meet your body's need for proper hydration. . Your individual need for water can increase for a variety of reasons. Exposure to extreme hot or cold weather, eating a high-fiber diet, being pregnant or breastfeeding a baby and vigorous exercise may all increase your need for water.
You can meet part of your water requirement through other fluids such as milk, juice and soup. Keep in mind that beverages containing caffeine or alcohol have a dehydrating effect and do not count toward your daily water intake.
Carbohydrates are starches or sugars and are found primarily in breads and cereals and in fruits and vegetables. The starches are referred to as complex carbohydrates, and sugars (found in fruits are well as in refined sugars) are called simple carbohydrates. Surprisingly, some of the complex carbohydrates may be digested, broken into sugars, and appear in the blood as sugars, almost as rabidly as simple sugars themselves. Cane or beet sugar, known technically as sucrose, and corn syrup, which contain the sugar known as fructose, make up a considerable portion of the average American diet.
Proteins are composed of building blocks called amino acids. Some of these amino acids can be produced by your body; others cannot. Those must be obtained from the diet called essential amino acids. The essential amino acids in meat, eggs, milk, and cheese are very efficiently used. Proteins found in vegetables, cereals (such as wheat, rice, or corn), peas, and beans (except for soy beans), do not provide an optimal ratio of essential amino acids. Thus, a greater amount of protein of plant origin is needed to meet your body's requirements than of protein or animal origin. Vegetarian diets when properly planned can readily meet one's needs for protein.
Fats are found in various foods and in various forms. Fats are found in foods of animal origin, such as meat, poultry, and fish, and in foods of vegetable origin. Some fats, such as cooking oil and salad oils, are liquid while others, much as butter, margarine, vegetable shortening, and trimmed meat fat, are solid at room temperature. Chemists classify fats according to the structure of their building blocks, the fatty acids. Fatty acids are saturated or unsaturated. Unsaturated fats are further classified as monounsaturated and polyunsaturated.
Various fatty acids have different effects on blood cholesterol levels, which have been shown to have a relationship to heart disease. Saturated fats tend to raise your total blood cholesterol by increasing both low density lipoprotein (LDL - “bad” cholesterol) and high density lipoprotein (HDL - the “good” cholesterol). Polyunsaturated fats tend to reduce your total blood cholesterol level, but at the expense of the protective HDLs.
Vitamins are substances that are essential in certain chemical transformations in your body and need to be present in your diet only in small amounts. They help the body to process proteins, carbohydrates, and fats. Certain vitamins also contribute to the production of blood cells, hormones, genetic material, and chemicals of your nervous system. Our bodies are unable to synthesize adequate amounts of most vitamins, so we must get them from the foods we eat. The essential vitamins (there are 13 in all) are divided into two categories: fat-soluble and water-soluble. The fat-soluble vitamins are A, D, E, and K. Vitamins A and D are stored in the liver, and reserve supplies may be sufficient for as much as 6 months. Reserves of vitamin K, however, may be sufficient for only a few days, and the supply of vitamin E is somewhere in between.
Both vitamins A and D can produce toxic effects when taken in excessive amounts. Toxic effects from taking large amounts of vitamin E have not been clearly demonstrated, but it does accumulate in the body's tissue. Vitamin K is scarcely stored at all, and toxic effects from taking large amounts have been found only rarely. The water-soluble vitamins include C (ascorbic acid) and B vitamins. They are stored to a lesser extent than fat-soluble vitamins. Although it is properly believed that the water-soluble vitamins are harmless when taken in large amounts, this is not always true.
Some of the water-soluble vitamins may have strong medicinal effects - good and bad - when taken in large amounts. Large amounts if niacin, for instance, are sometimes used to reduce high levels of fats in the blood; on the other hand, they also can cause abnormal liver function and increase in blood sugar levels. Ascorbic acid in high amounts can increase oxalate excretion in the urine and may promote oxalate kidney stones. In large doses, pyridoxine (a B vitamin) can cause nerve damage. In short, taking mega doses of vitamins is rarely warranted - and often potentially hazardous
