Dietary fiber is part of every plant food. Although it is most often a carbohydrate, dietary fiber is calorie free in humans because we don’t possess the enzymes to break it down.
Many different components in plant foods are categorized as dietary fibers, and not all fiber is the same. One way of grouping fiber is by how easily it dissolves in water in the body.
Soluble fiber partially dissolves in water, forming a jelly-like bulk in the stomach and in the small intestine that’s associated with fullness, lower blood cholesterol levels and lower blood glucose concentrations. Oatmeal, oat bran, apples, citrus fruits, legumes, and psyllium (a plant product used in common over-the-counter fiber and laxative supplements) are particularly rich in soluble fiber.
Several scientific studies have found a link between soluble fiber intake and a lower cholesterol level in the blood. Elevated blood cholesterol levels are a risk factor for heart disease. The U.S. Food and Drug Administration (FDA) allows a health claim like the following on the labels of food products that contain a minimum of .75 grams per serving of soluble fiber from whole oats: “Soluble fiber from foods such as oat bran, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.”
As the name implies, insoluble fiber does not dissolve in water. Insoluble fibers add bulk in the colon and help the body retain water, resulting in softer and larger stools that pass faster, helping to prevent constipation. Whole grains, bran, nuts, and vegetables are especially good sources of insoluble fiber.
The differences between soluble and insoluble fiber are important when it comes to dietary fiber’s effect on your health, but not when considering how much fiber to eat every day. Expert recommendations for daily fiber intake do not specify how much of each type of fiber to eat. Every plant food contains a mixture of soluble and insoluble fiber, so a high-fiber diet provides healthy amounts of both types. *






