Food provides nutrients, chemical substances that are essential for life and necessary for providing energy, building and maintaining body organs, and for various metabolic processes.
Nutrients have three functions:
Carbohydrates are the major source of energy for the body. They are divided into simple sugars (like table sugar) and complex carbohydrates (like fiber). The body utilizes most carbohydrates to generate glucose, which serves as the basic functional molecule of energy within the cells of the human body.
Proteins have a variety of uses, including serving as a source of energy, as substrates for tissue growth and maintenance, and for certain biological functions, such as making structural proteins, transfer proteins, enzyme molecule, and hormone receptors. Proteins are also the major component in bone, muscle, and other tissue and fluids. There are proteins from animal sources (meat, poultry, milk, fish) and from plant sources (wheat, corn, rice and beans).
Lipids (fats and oils) are high-energy yielding molecules and, when composed in triglycerides, the major form of energy storage in the body.
Vitamins are chemical compounds that are required for normal growth and metabolism. Some vitamins are essential for a number of metabolic reactions that result in the release of energy from carbohydrates, fats and proteins.
Minerals are inorganic compounds playing a vital role in several physiological functions, including critical involvement in nervous system functioning, in cellular reactions, in water balance in the body and in structural systems, such as the skeletal system.
Water has many necessary functions in the human body. It is used as a solvent, as a lubricant, as a conduction system for transportation of vital nutrients and unnecessary waste, and as a mode of temperature regulation.