Proteins make up most of the body weight after water. Proteins are required for growth and development of all body tissues. They are the major source of building material for muscles, blood, skin, hair, nails, and internal organs, including the heart and brain. Protein is needed for the formation of hormones which control a variety of body functions such as growth, sexual development, and rate of metabolism. Protein also helps prevent the blood and tissues from becoming either too acid or too alkaline and helps regulate the body’s water balance.

Proteins are more complex than carbohydrates or fats. When a protein food is ingested, the body breaks it down into amino acids. Ribosomes in each cell receive coded messages from DNA in the cell nucleus on how to put these amino acids together in chains. There are 20 amino acids and they can be combined in numerous ways, like the letters in the alphabet. When a protein chain is finished, its chemical, electrical, and sequential (the sequence of amino acids) characteristics result in a unique coiled three-dimensional shape which is important because the shape alone enables the protein to perform a specific function.

Fats are one of the essential nutrients required by our body. Fats consist of a wide group of compounds, generally insoluble in water but soluble in organic solvents.

Fats are converted for storage in the body from glucose. We also derive fats directly from foods. Fats are a mixture of fatty acids composed of carbon molecules linked together with attached hydrogen and oxygen atoms. This carbon–carbon configuration is of high-energy and therefore caloric value of fats is twice the caloric value of carbohydrates. Though Carbohydrates are the principal source of energy to our body, fats are our energy reserve.
Fats insulate the body and cushion vital organs. Almost all the cells in the body can convert fats into energy, a process called fatty-acid oxidation. Most fatty acids are in the form of triglycerides, a combination of fatty acids and a carrier molecule, glycerol. When we eat fats and oils, the body separates the fatty acids from their carrier; likewise when triglycerides in fat tissue are taken out of storage for conversion to energy. Every cell in the body needs fatty acids to produce and build new cells. They are critical in the transmission of nerve impulses and for normal brain development.

Fat has received bad reputation in the diet world, although only some of that reputation is deserved. While bad fats can contribute to poor health, some fats are needed for good health. Better understanding of types of fats and functions of various fats would help us understand more about the fats we need and the fats to avoid.

Carbohydrates in food are the main source of energy required by various body functions and muscular effort. They are necessary for the digestion and assimilation of other food elements, including regulation of protein and fat metabolism.

Types of Carbohydrate: Carbohydrates structurally are carbon, hydrogen, and oxygen molecules arranged in the form of rings. Simple carbohydrates like glucose, fructose (sugar in fruits), and galactose (sugar in milk) are composed of one single ring and are called monosaccharides. Sucrose (found in sugar cane and sugar beets), maltose (found in grains), and lactose (in milk) are composed of two rings linked together and are called disaccharides. The two rings in sucrose are made up of glucose plus fructose; maltose is glucose plus glucose; and lactose is glucose plus galactose. Disaccharides are broken into monosaccharide during digestion. Fiber is a carbohydrate but consists of very large molecules that are resistant to enzymatic action.

The human body, especially the brain, needs a constant supply of glucose. There are hormonal mechanisms that regulate glucose metabolism. Improper glucose metabolism may lead to obesity and diabetes. Hypoglycemia is condition when Glucose levels drop resulting in weakness and fatigue. Reducing sugar and eating small frequent meals focusing on whole grains, seeds, nuts, legumes, fresh fruits, and vegetables, low fat dairy, yogurt, and fish can aid in stabilizing blood sugar levels.

The foods we eat are chemically complex. They must be broken down by the body into simpler chemical forms which can be absorbed through the intestinal walls and transported by the blood to the body cells. In the cells, these nutrients provide energy and the correct building materials to sustain life.

Digestion is a series of physical and chemical changes by which food, taken into the body, is broken down in preparation for absorption from the intestinal tract into the bloodstream. These changes take place in the digestive tract, which includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

Beginning in the mouth, chewing breaks large food pieces into smaller. Food that is masticated well allows for more complete enzymatic action. If left in chunks, food that passes into the stomach and intestine will likely remain undigested as enzymes are only able to work on the surface of these larger particles. The enzyme that is secreted in the mouth from the salivary glands is ptyalin. Ptyalin is necessary for the breakdown of carbohydrates.