Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
20.3.2 ABSORPTION OF MINERALS, BILE ACIDS, AND CHOLESTEROL
Levels of calcium, bile acids, cholesterol, and other compounds in the human
organism are dependent on the intake of digestible and nondigestible saccharides.
Intestinal absorption of calcium increases with the ingestion of several carbohydrates.
In some people, glucose or galactose administered orally fractionally
increases calcium absorption. In healthy adults, such increase may reach 30%. The
effect of lactose on calcium intake is controversial. In experimental animals, a diet
containing either inulin or resistant starch (5 to 20%) improves uptake of calcium,
iron, and zinc. In humans, inulin stimulates the absorption of calcium, but has no
such effect on the absorption of zinc, iron, or magnesium. In this instance, however,
experimental doses of inulin were below 15 to 40 g/day.
These observations can be rationalized in terms of osmotic action of oligosaccharides,
acidification of intestine content by bacterial fermentation, formation of
readily soluble magnesium and calcium salts of lower fatty acids generated on
fermentation, or secondary hypertrophia of mucous membrane of the colon. There
are also suggestions that fiber (some carbohydrates) can complex minerals such as
calcium, iron, copper, magnesium, phosphorus, and zinc. The resulting complexes
are insoluble and reduce bioavailability of these essential minerals. 4
Fiber in the diet, especially pectins, complexes bile acids and reduces cholesterol
intake. Tests with rats fed with a diet containing 10% w/w inulin showed a decrease
in the level of triglycerides and cholesterol void as well as after a meal. About 12
to 36 g of pectins in the human daily diet reduces the total serum cholesterol by 8
to 30%. However, relevant data in healthy people are not univocal.
20.4 SACCHARIDES AS ENERGY SOURCE FOR THE
ORGANISM
20.4.1 NUTRITIONAL VALUE OF SACCHARIDES
Throughout their life, humans ingest about 10,000 kg of carbohydrates. Digestible
carbohydrates are the main source of energy. In developed countries, carbohydrates
supply 45 to 60% of the energy requirement, but in the Third World such requirement
is fulfilled in less than 85% of the population. Adults in Europe daily consume about
240 g of glucose, 65 g of fructose, and 15 g of galactose (only monosaccharides are
absorbed from the gut); however, polysaccharides, mainly starch, predominate. Only
thermally processed and pasted starch is digested in the gut. Such starch undergoes
enzymatic hydrolysis to monosaccharides by salivary and pancreatic amylase, glucoamylase,
amyloglucosidase, and disaccharidases from intestinal mucosa.
Monosaccharides are absorbed from the intestine into the portal circulation and
transported with blood to the liver, where fructose and galactose are converted into
glucose. In the systemic circulation only glucose is present. The concentration of
glucose in blood increases in the postprandial period. At that time, tissues utilize
glucose absorbed directly from the gut. An excess of glucose is stored as glycogen,
and excessive glucose, which cannot be transformed into glycogen, is metabolized
to triglycerides.