Digestion begins before you ever place a piece of food in your mouth. When you smell, see, or even imagine food, your mouth produces saliva -- the first step in the long digestion process. The ultimate goal of digestion is to break down food into particles small enough to be absorbed into your bloodstream. The nutrients absorbed in digestion include the three major nutrients: carbohydrates, proteins and fats, as well as the minor nutrients: vitamins and minerals.
Digestive Process
The saliva you produce before eating contains enzymes that break down food and make it easier to swallow. Your teeth help out by tearing food into pieces small enough to move comfortably through your esophagus. Once you swallow, powerful muscles push food downward through your esophagus, where hydrochloric acid, enzymes and your churning stomach muscles work together to break food down even further. The food is then deposited into your small intestine. At this point, the food has been broken down so far that individual molecules are small enough to pass through the intestinal walls, where the bloodstream picks them up and carries them where they're needed. Undigested food portions travel through the large intestine, where they are dried, compacted and eventually expelled.
Carbohydrates
Carbohydrates, or sugars and starches, are carbon and hydrogen molecules linked together in chains, which might contain just a few molecules, or long strands with complex branches. During digestion, carbs break down into their simplest form: sugar. The sugar is converted to glucose, which your body uses to perform all of its normal functions.
Proteins
Proteins are long, complex chains of amino acids found in foods such as meats, cheeses, eggs, rice and some vegetables. During digestion, your body breaks the chains back down to their original amino acids, then rebuilds the new chains it needs to form muscles, skin, hair, nails and cell walls.
Fats
Bile salts and pancreatic secretions break down fats in the small intestine. Fats pass through the intestinal wall in molecular form just like other nutrients, but whether they do so as fatty acids or glycerides is disputed. The fat that enters the bloodstream is used to create energy stores, store vitamins, insulate the body, produce hormones and rebuild cells.
Vitamins
Vitamins are essential organic micronutrients. They include vitamins A, C, D, E, K and the B-complex vitamins. Vitamins join with enzymes and minerals to perform thousands of different functions, from regulating hydration, to supporting eyesight, to defending the body against harmful free radicals. Vitamins C and B-complex are water soluble, which means they dissolve into the bloodstream, and any excess is excreted through your urine. Vitamins A, D, E and K are fat soluble, meaning they dissolve into your body's fat stores and are released when needed.
Minerals
Minerals are inorganic micronutrients found in soil, sand and rocks. They include calcium, magnesium, iron, phosphorus, potassium, zinc, sodium, copper, fluoride, chloride, molybdenum, selenium, sulfur and cobalt. Minerals help manage your body's heart, nerve and muscle functions; regulate the production and use of hormones in your endocrine system; keep your body fluids balanced; and support your metabolism. The most essential mineral, iron, ensures that all of your body's cells contain oxygen.
