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There are many different types of fiber that can be distinguished by their chemical structure. They include:

• Cellulose. The chief constituent of all plant cells walls. It is found naturally in all vegetables, fruits and legumes. It also can be extracted from wood pulp or cotton. When extracted, this type of fiber is added to foods and serves as an anticaking, thickening and texturizing agent.
  
  
• Gums and mucilages. Gums are the substances secreted by plants when they are cut. Guar gum and gum arabic are used as additives to thicken processed foods. Mucilages resemble gums and types such as psyllium (also a common fiber supplement) and carrageenan are added to foods as stabilizers.
  
  
• Hemicelluloses. The main component of all grain fibers.
  
  
• Lignan. A tough fiber not found in many foods. The woody parts of some vegetables (e.g., carrots) and the small seeds of fruits such as strawberries are made up of lignan.
  
  
• Pectins. Commonly found in vegetables and fruits (e.g., citrus fruits, apples), they easily form gels in water. Pectins sometimes are isolated and used to thicken jelly, prevent separation of salad dressings and provide texture and consistency for various products.
  
  
• Resistant starches. Some starches are classified as fibers because they are not digested or absorbed by the body. This type of starch is found in whole legumes, raw potatoes and unripe bananas and plantains.