Nutrient, vitamin and mineral assimilation, along with water and electrolyte absorption, plays an important role in sustaining life. Unfortunately, all too often, a disease points out the impor­tance of these processes to the patient and his doctor. Mechanical and enzymatic degrada­tion of food to its basic constituents (digestion) begins in the oral cavity and is continued along the gastrointestinal tract, all the way down to the small intestine and within it. Here, the major­ity of nutrients, electrolytes, minerals, vitamins, and water are absorbed. Colon then typically fine-tunes the amount of water and electrolytes to be absorbed/excreted. The abovementioned digestive degradation to smaller molecular particles is common to all major nutrients and necessary to ensure their solubility in the watery milieu of lumen, intracellular space and plasma and, most importantly, to make them cross the intestinal epithelial barrier. Due to differences in chemical composition across different groups of nutrients, the mechanisms of their intraluminal breakdown and transepithelial transport differ.