This section of the book is from the "How and When to Be Your Own Doctor" book, by Dr. Isabelle A. Moser with Steve Solomon, published in 1997.
Digestion is a huge, unappreciated task, unappreciated because few of us are aware of its happening in the same way we are aware of making efforts to use our voluntary muscles when working or exercising. Digestion begins in the mouth with thorough chewing. If you don"t think chewing is effort, try making coleslaw in your own mouth. Chew up at least half a big head of cabbage and three big carrots that have not been shredded. Grind each bit until it liquefies and has been thoroughly mixed with saliva. I guarantee that if you even finish the chore your jaw will be tired and you will have lost all desire to eat anything else, especially if it requires chewing.
Making the saliva you just used while chewing the cabbage is by itself, a huge and unappreciated chemical effort.
Once in the stomach, chewed food has to be churned in order to mix it with hydrochloric acid, pepsin, and other digestive enzymes. Manufacturing these enzymes is also considerable work! Churning is even harder work than chewing but normally, people are unaware of its happening. While the stomach is churning (like a washing machine) a large portion of the blood supply is redirected from the muscles in the extremities to the stomach and intestines to aid in this process. Anyone who has tried to go for a run, or take part in any other strenuous physical activity immediately after a large meal feels like a slug and wonders why they just can"t make their legs move the way they usually do. So, to assist the body while it is digesting, it is wise to take a siesta as los Latinos do instead of expecting the blood to be two places at once like los norteamericanos.
After the stomach is through churning, the partially digested food is moved into the small intestine where it is mixed with more pancreatin secreted by the pancreas, and with bile from the gall bladder. Pancreatin further solubilizes proteins. Bile aids in the digestion of fatty foods. Manufacturing bile and pancreatic enzymes is also a lot of effort. Only after the carbohydrates (starches and sugars), proteins and fats have been broken down into simpler water soluble food units such as simple sugars, amino acids and fatty acids, can the body pass these nutrients into the blood thorough the little projections in the small intestines called villi.
The leftovers, elements of the food that can"t be solubilized plus some remaining liquids, are passed into the large intestine. There, water and the vital mineral salts dissolved in that water, are extracted and absorbed into the blood stream through thin permeable membranes. Mucous is also secreted in the large intestine to facilitate passage of the dryish remains. This is an effort. (Intestinal mucous can become a route of secondary elimination, especially during fasting. While fasting, it is essential to take steps to expel toxic mucous in the colon before the poisons are re adsorbed.) The final residue, now called fecal matter, is squeezed along the length of the large intestines and passes out the rectum.
If all the digestive processes have been efficient there now are an abundance of soluble nutrients for the blood stream to distribute to hungry cells throughout the body. It is important to understand the process at least on the level of oversimplification just presented in order to begin to understand better how health is lost or regained through eating, digestion, and elimination. And most importantly, through not eating.