Every single cell throughout your body works around the clock every day. They need a steady supply of fuel to give them the energy to do their specialized jobs, though. The fuel that cells prefer to use is called glucose, which is the simplest form of carbohydrate. Both starches and sugars eventually turn into glucose, although the digestive process is different for each one.
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Breaking Down Starch
Starch compounds are big and complex. When you chew something high in starch, like a potato or slice of bread, cells in your mouth automatically excrete saliva, an enzyme-containing digestive juice. Saliva’s job is to pull apart all of those sugars, so you swallow simpler carbohydrate sugar molecules, rather than complex starch compounds. Once the simple sugars reach your stomach, specialized cells secrete more digestive substances that combine with all broken-down food particles. Everything gets mixed together into a partially digested substance called chyme, which gets pushed to your small intestine for further digestion.
Saliva doesn't break down sugar the way it breaks down starch. Instead those sugar molecules travel down to your stomach, get blended into the chyme mixture and head toward your small intestine. Digestive enzymes in the small intestine convert sugars -- whether they were sugars originally or were converted into sugars from starch -- directly into glucose. After this quick conversion step, glucose molecules get absorbed through intestinal walls, with the help of tiny intestinal “fingers” called villi.
Glucose Absorption and Storage
When glucose goes through your intestines, it immediately enters your bloodstream. This makes your brain send a signal to your pancreas to release insulin, a type of hormone. Insulin acts as a gatekeeper, opening up cell walls so glucose can go inside. Cells can either snag what they need to fuel them right away or store the glucose to use later on. Glucose that goes into storage mode gets converted into a polysaccharide, a complex type of carbohydrate called glycogen. Your muscles and liver store glycogen, which can be converted back into glucose fuel quickly, just in case you don’t have enough glucose coming in from your diet.
Even though fiber’s primary job is getting food to move through your gut -- it never converts into glucose -- it does have a role in glucose processing. Soluble fiber, the kind you get from oats, beans and fruits, turns into a thick, slow-moving material as it absorbs water. This sludge slows digestion, which in turn, delays glucose absorption. It allows glucose to get absorbed a little at a time in your small intestine, rather all together. If you’re diabetic, soluble fiber should make it easier for you to have more stable blood glucose levels.