Macronutrients in Health and Disease: Carbohydrate

Carbohydrate is the main energy source in the human diet, providing 50% or more of total calories in the form of starches and sugars. Carbohydrate–containing foods can be classified in several clinically relevant ways:

Simple vs. Complex Carbohydrate

The term “simple carbohydrate” refers to mono– and disaccharides. Common monosaccharides include glucose and fructose, while common disaccharides include sucrose. Figure 1, Figure 2, and Figure 3 represent the chemical structures of glucose, fructose, and sucrose.

Figure 1: Glucose (monosaccharide)

C6H12O6

Figure 2: Fructose (monosaccharide)

C6H12O6

Figure 3: Sucrose (disaccharide)

C12H22O11

Complex carbohydrate refers to polysaccharides; the word is synonymous with “starch”. The health benefits of carbohydrate–containing foods are largely limited to those rich in complex (rather than simple) carbohydrates. Foods high in simple carbohydrate include table sugar, fruit, and milk. Foods high in complex carbohydrate include grains, legumes, starchy vegetables, pasta, and breads. Starches are branched carbohydrates that include glycogen (‘animal starch’), amylopectin, amylose, and cellulose, an important source of dietary fiber (see below).

Figure 4: Cellulose

Figure 5: Partial Structure of Amylose