Nutrition Science and Everyday Application - beta v 0.1

440 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
amino acids) were responsible for preventing what we know now as vitamin deficiencies. He
coined the term “vitamines” to describe these organic substances that were recognized as
essential for life, yet unlike other organic nutrients (carbohydrates, protein, and fat), do not
provide energy to the body. Eventually, when scientists discovered that these compounds
were not amines, the ‘e’ was dropped to form the term “vitamins.” 1
Classification of Vitamins
Vitamins are essential, non-caloric, organic micronutrients. There is energy contained in the
chemical bonds of vitamin molecules, but our bodies don’t make the enzymes to break
these bonds and release their energy; instead, vitamins serve other essential functions in the
body. Vitamins are traditionally categorized into two groups: water-soluble or fat-soluble.
Whether vitamins are water-soluble or fat-soluble can affect their functions and sites of
action. For example, water-soluble vitamins often act in the cytosol of cells (the fluid inside
of cells) or in extracellular fluids such as blood, while fat-soluble vitamins play roles such as
protecting cell membranes from free radical damage or acting within the cell’s nucleus to
influence gene expression.
Figure 8.1. Classification of vitamins as water-soluble or fat-soluble.
One major difference between water-soluble and fat-soluble vitamins is the way they are
absorbed in the body. Water-soluble vitamins are absorbed directly from the small intestine