Molecules found in foods can be absorbed by multiple routes.
Carbohydrates, proteins and lipids are broken down into
monosaccharides, amino acids and fatty acids, respectively, by
diverse hydrolases secreted in the gut lumen or associated with
membranes of intestinal epithelial cells (IECs). These food
components are actively transported via specific carrier
molecules on the surface membrane of IECs and used as
nutrients (Fig. 1). Vitamins and minerals in foods are also
absorbed through IECs by passive diffusion or active transport
using specific carrier molecules (Fig. 1). The main role of
vitamins and minerals is to regulate the various physiological
functions of cells.