by pepsin, which needs an acid medium to release its full potency. For this reason I have recommended hydrochloric acid tablets in many of the suggested diets to maintain the normal condition of the stomach, which is definitely on the acidic side. Ordinary meals will pass through the stomach to the small intestine in three or four hours, wh le substances that are watery, like soups and juices, pass through quickly. Carbohydrate substances leave the stomach first and are followed by the proteins. Fats remain for the longest time, accounting for the feeling of fullness after eating meals high in fat content.
When the partially digested food leaves the stomach it enters the small intestine, where the main absorption of nutrients takes place. It is first acted on by the pancreas, a gland located just beneath the stomach that manufactures and secretes juices containing some of the body's most important digestive enzymes. Amylase completes the digestion of starch molecules begun by the enzyme ptyalin in the mouth; lipases split fats; and proteases continue the digestion of proteins begun by pepsin in the stomach.
The absorption of nutrients is accomplished by millions of villi, fingerlike projections lining the intestinal walls. Each one has a miniature, complete blood system with an artery carrying blood in and a vein carrying it out As food is digested, villi pick up the particles and pass them into the veins. During this process food is converted into nutrients capable of being absorbed into the bloodstream Carbohydrates are converted into glucose and fructose, fats become fatty acids, and protein is broken down into amino acids Dietary vitamins in food are absorbed with water and fat, while minerals found in food are absorbed with water. The only nutrients not requiring digestion are vitamin and mineral supplements and some types of sugar, such as glucose. Because their chemical structure is elementary, they do not undergo chemical changes but are dissolved by fluids in the digestive tract and pass directly into the bloodstream. Only alcohol is absorbed directly through the stomach walls. Any products left undigested
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