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By Toby Smithson, Alan L. Rubin

Glucose is a simple sugar that is extremely important to you as a source of energy. It’s the key ingredient in a biochemical recipe that produces a powerhouse molecule adenosine triphosphate, best known by its initials ATP. ATP is your fuel, the source of the energy you use to move or to think or, for that matter, to generate the heat needed to remain a steady 98.6º Fahrenheit.

The conversion of glucose to energy via ATP takes place inside of the cell membranes of trillions and trillions of individual cells, most all of which are properly equipped to prepare the recipe for ATP in structures called mitochondria.

And, because blood already visits cells in your farthest outreaches to deliver oxygen and remove wastes, blood also conveniently brings glucose right to the doorstep of cells that need it to make energy. Your body can convert other ingredients to energy if necessary, but glucose is the first choice.

You get glucose from food, and you eat a lot more glucose than you might think, even if you don’t have an overactive sweet tooth. Actually, glucose isn’t that sweet anyway.

Virtually all of the glucose you eat is locked in chains with other sugars or more glucose — polysaccharides. If the chains are small the molecule is still considered a sugar — table sugar (sucrose) is one molecule of glucose and one fructose — a disaccharide.

If the chains are longer, even to hundreds or thousands of glucose molecules, the molecules are starch or fiber. Taken together, sugars, starches, and fiber are carbohydrates, a word you’re surely familiar with if you have diabetes.

Most dietary carbohydrates come from plants. Plants are constructed in large measure of the carbohydrate cellulose, and cellulose can include thousands of linked glucose molecules. As a carbohydrate, cellulose is definitely in the fiber category and not a very digestible fiber at that.

If humans could easily digest cellulose, you might have a favorite old-family recipe for cotton ball sauté or cedar planked plank. Fortunately, plants also make more digestible and more flavorful carbohydrates.

The only dietary carbohydrate you get from animals is lactose, or milk sugar. Lactose in mother’s milk is how infants (and puppies and calves) get carbohydrates for energy, but the ability to digest lactose diminishes in most humans after infancy. As a result, an estimated 65 percent of the human population is lactose intolerant to some degree.

Glucose as a single molecule is liberated from its chain gang polysaccharides by various digestive processes, starting right in your mouth with saliva. By the time your food passes through your stomach, small intestine, and maybe the first portion of your colon all of the easily digestible carbohydrate has been broken apart by specific enzymes, finally freeing the individual glucose molecules. At that point, glucose is ready to be captured.

Just because fiber is less digestible and may not surrender its glucose easily doesn’t mean it isn’t a very important part of a healthy diet.

Within your intestinal tract are millions of fingerlike projections called villi, which are especially rich in blood supply. Before liberated glucose can escape through the colon as waste material, the molecules are absorbed directly into your bloodstream through small capillaries in a process called active transport.

Much glucose absorption occurs in the first part of your small intestine, and absorption is very efficient due to the vast surface area of millions of villi. The process is also relatively quick, so eating carbohydrate food results in a surge of glucose entering the bloodstream. Rising blood glucose levels are a serious insult to homeostasis.