Chitosan, derived from oyster shells, has also been used to lower cholesterol levels. (For further discussion of the health aspects of fiber, see the beginning of Chapter 8, Foods.)
Although the carbohydrate-containing foods often constitute the majority of our diet, there are no specific requirements published for our carbohydrate needs. They are one of the best sources of energy and are simple for the body to use; however, since the body can make its own glucose from stored glycogen and the amino acid L-alanine, the government lists no minimum requirement. Yet, carbohydrate intake is important to health. Many of the carbohydrate foods contain essential vitamins and minerals as well as the dietary fiber necessary for colon health and proper elimination.
On the other hand, people can live without carbohydrate intake; in fact, in many weight loss programs carbohydrate consumption is severely limited. It is wise in these cases to consume supplemental fiber. Also, some people have a tendency to overeat carbohydrate foods, even to become “carb addicts.” With this, weight may increase; obesity is associated most frequently with carbohydrate overindulgence. Allergies and emotional shifts, including “carbohydrate depression,” have also been associated with sensitivity to overconsumption of this macronutrient.
Peoples of different cultures consume varying amounts of carbohydrates. Native or traditional diets may be very high in carbohydrates, while in cold climates, as with the Eskimo culture, people may consume very few carbohydrates. The average American diet includes about 40–50 percent carbohydrates; sadly enough, about half of that is from the refined and processed flours and sugars in breads, candies, cookies, and cakes. These foods deplete the body of many B vitamins and of minerals such as chromium. In addition to the already-mentioned diseases of obesity and tooth decay, it is possible that this type of diet (high in simple and refined sugars, high in fats, and low in complex carbohydrates) may be influencing the incidence of diabetes, high blood pressure, heart disease, anemia, skin problems, kidney disease, and cancer.
I feel that a diet of about 60–70 percent carbohydrate foods is ideal, especially when caloric consumption will support our best weight range. Intake of the refined carbohydrate foods should be minimal; primary intake should be the complex carbohydrates (many vegetables, whole grains, and legumes) and some simple “naturally occurring” sugars from the fruits and vegetables. For the adult, this higher carbohydrate/fiber diet, along with about 15–25 percent fat and 15–20 percent protein, is likely to be the best long-range healthy diet.
Carbohdrate Digestion and Metabolism
Carbohydrates—sugars and starches—are broken down in the gastrointestinal tract by various enzymes for absorption into the blood. The disaccharides (lactose, sucrose, and maltose) are converted into their monosaccharides (glucose, fructose, and galactose). The polysaccharides (starches) are converted by salivary amylase in the mouth into dextrin, a shorter-chain starch; then the dextrins are reduced to maltose by pancreatic amylase released into the small intestine.
The maltose is further broken down into glucose by maltase enzymes at the intestinal lining. Also in the small intestine, sucrose is changed into glucose and fructose by the enzyme sucrase, while lactase converts lactose, the milk sugar, into glucose and galactose. The monosaccharides, or simple sugars, such as glucose, galactose, and fructose, are the end products of carbohydrate digestion and are all absorbed into the bloodstream through the intestinal lining. The blood circulates to the liver, where fructose and galactose are easily converted into glucose, the fuel the body uses for energy.