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The food we eat provides us with a variety of nutrients, specific substances found in food that perform one or more biochemical or physiological functions in the body. Six general classes of nutrients are considered necessary in human nutrition. They are carbohydrates, fats, proteins, vitamins, minerals and water. Within several of these general classes (notably proteins, vitamins, and minerals), there are a number of specific nutrients necessary for life. For example, over a dozen vitamins are needed for optimal physiological functioning. Although several of these nutrients may be manufactured in our bodies, such as vitamin D through the action of sunlight on the skin, the vast majority need to be obtained through the diet.

 Table 6.1 presents the specific nutrients known to be essential or probably essential to humans at this time. Some of the nutrients listed have been shown to be essential for various animals and are theorized to be essential for humans. It is possible that this list may be expanded in the future as more accurate analytical methods are developed to study the effects of certain nutrients or phytochemicals in human nutrition. Although carbohydrates are not an essential nutrient in the strictest sense, many nutritionists consider dietary fiber, which is primarily carbohydrate, a specific necessity in the diet for prevention of certain health problems.

 These nutrients perform three major functions. First, they provide energy for human metabolism. Carbohydrates and fats are the prime sources of energy. Second, nutrients are used to build and repair body tissues. Protein is the major building material for muscles, other soft tissues, and enzymes, while certain minerals such as calcium and phosphorus make up the skeletal framework. Third, nutrients are used to help regulate body processes. Vitamins, minerals, and proteins work closely together to maintain the diverse physiological processes of human metabolism. For example, hemoglobin in the red blood cell (RBC) is essential for the transportation of oxygen to the muscle tissue via the blood. Hemoglobin is a complex combination of protein and iron; however, other minerals and vitamins are needed for its synthesis and for full development of the RBC. Since space does not permit a detained discussion of each specific nutrient, we will cover briefly the general role of each major nutrient in human metabolism and focus upon some of the major health implications as supported by current epidemiological or experimental search.

 Table 6.1 Essential Nutrients

 1.       Proteins (Essential Amino Acids)

 histidine       phenylalanine
isoleucine     threonine
leucine         tryptophan
lysine           valine
methionine

 2.       Fats (Essential Fatty Acids)

 linoleic         alpha-linolenic 

3.       Carbohydrates Fiber 

4.       Vitamins
          Water-soluble                  Fat-soluble
          B Complex                      A (Retinol)
          B1(Thiamin)                   D (Calciferol)
          B2 (Riboflavin)               E (Tocopherol)
               Niacin                             K (Phylloquinone)
          B6 (Phridoxine)
          Pantothenic acid
          Folacin
          B12(Cyanocobalamin)
          Biotin
          C (Ascorbic acid)

5.       Minerals 

             Calcium       Iron                       Selenium
          Chloride      Magnesium            Silicon
          Chromium   Manganese            Sodium
          Cobalt         Molybdenum         Sulfur         
         Copper        Nickel                   Tin
          Fluoride       Phosphorus           Vanadium
          Lodine         Potassium             Zinc 

6.       Water 

Essential nutrients are necessary for human life. An inadequate intake may result in disturbed body metabolism, certain disease states, or death. 

Some of the nutrients listed have been shown to be essential for various animals and are probably essential for humans. Essential nutrients, or nutrients from which they may be formed, must be obtained from the foods we eat.