Starch and fiber are both complex carbohydrates, but your body processes them in very different ways — one provides energy, while the other meets non-energy nutritional needs. For optimal health, most people should get 40 to 60 percent of total calories from non-fiber carbohydrates and eat 14 grams of fiber for every 1,000 calories consumed. This can vary based on individual needs, though, so talk to your doctor before making major changes to your diet.
Carbohydrates are labeled as either complex or simple, and starch and fiber are the two types of complex carbs. All carbs are made of sugar molecules, but simple carbs such as table sugar, honey and lactose from milk contain just one or two molecules, while complex carbs, found in potatoes, beans and grains, contain three or more molecules. This means that your body must work harder to convert complex carbs into glucose, or blood sugar, which you use for fuel. In contrast, glucose from simple carbs — also referred to as sugars — is absorbed rapidly into the bloodstream. Simple carbs typically provide little nutrition other than energy, and are thus dubbed “empty calories.”
Fiber, also called cellulose, provides the structure for cell walls in plants — you’ll find it in vegetables, fruits, nuts and grains. Although fiber is a carbohydrate, your body can’t break it down into glucose or any other usable energy source; therefore, it technically contains no calories. However, fiber still plays an important role in nutrition. It aids in digestion, encouraging regular bowel movements while helping to prevent hemorrhoids and diverticulosis, a condition in which small pockets form in the colon that may become inflamed or infected. Fiber is classified as either soluble or insoluble, and soluble fiber, found in oatmeal and bran, may also help maintain healthy cholesterol levels.
Starches are carbohydrates that plants store as energy for later use, just as humans store glycogen, a form of glucose, in our muscles for reserve fuel. When people consume starchy foods such as grains and peas, enzymes in the body help break the starches down into usable glucose. Starch digestion begins with salivary enzymes in the mouth, which is why bread begins to taste sugary as you chew it.
Starch and Fiber in Foods
Fiber is often removed during food processing, so refined grains are left with a higher percentage of starch. This is why whole-wheat bread and brown rice contain more fiber than white bread and rice. For example, a serving of whole wheat spaghetti contains 4.5 grams of fiber, while the same amount of white spaghetti contains just 1.8 grams. Similarly, 1 cup of cooked brown rice contains 3.5 grams of fiber while the same serving of white rice has just 1.6 grams. Even removing the skin of a potato cuts the fiber content by about half.